Adding upstream version 4.19.249.upstream/4.19.249upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

11 files changed, 12933 insertions, 0 deletions

diff --git a/kernel/cgroup/Makefile b/kernel/cgroup/Makefile
new file mode 100644
index 000000000..bfcdae896
--- /dev/null
+++ b/kernel/cgroup/Makefile
@@ -0,0 +1,8 @@
+# SPDX-License-Identifier: GPL-2.0
+obj-y := cgroup.o rstat.o namespace.o cgroup-v1.o
+
+obj-$(CONFIG_CGROUP_FREEZER) += freezer.o
+obj-$(CONFIG_CGROUP_PIDS) += pids.o
+obj-$(CONFIG_CGROUP_RDMA) += rdma.o
+obj-$(CONFIG_CPUSETS) += cpuset.o
+obj-$(CONFIG_CGROUP_DEBUG) += debug.o
diff --git a/kernel/cgroup/cgroup-internal.h b/kernel/cgroup/cgroup-internal.h
new file mode 100644
index 000000000..8f7729b0a
--- /dev/null
+++ b/kernel/cgroup/cgroup-internal.h
@@ -0,0 +1,276 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __CGROUP_INTERNAL_H
+#define __CGROUP_INTERNAL_H
+
+#include <linux/cgroup.h>
+#include <linux/kernfs.h>
+#include <linux/workqueue.h>
+#include <linux/list.h>
+#include <linux/refcount.h>
+
+#define TRACE_CGROUP_PATH_LEN 1024
+extern spinlock_t trace_cgroup_path_lock;
+extern char trace_cgroup_path[TRACE_CGROUP_PATH_LEN];
+
+/*
+ * cgroup_path() takes a spin lock. It is good practice not to take
+ * spin locks within trace point handlers, as they are mostly hidden
+ * from normal view. As cgroup_path() can take the kernfs_rename_lock
+ * spin lock, it is best to not call that function from the trace event
+ * handler.
+ *
+ * Note: trace_cgroup_##type##_enabled() is a static branch that will only
+ *       be set when the trace event is enabled.
+ */
+#define TRACE_CGROUP_PATH(type, cgrp, ...)				\
+	do {								\
+		if (trace_cgroup_##type##_enabled()) {			\
+			spin_lock(&trace_cgroup_path_lock);		\
+			cgroup_path(cgrp, trace_cgroup_path,		\
+				    TRACE_CGROUP_PATH_LEN);		\
+			trace_cgroup_##type(cgrp, trace_cgroup_path,	\
+					    ##__VA_ARGS__);		\
+			spin_unlock(&trace_cgroup_path_lock);		\
+		}							\
+	} while (0)
+
+struct cgroup_pidlist;
+
+struct cgroup_file_ctx {
+	struct cgroup_namespace	*ns;
+
+	struct {
+		void			*trigger;
+	} psi;
+
+	struct {
+		bool			started;
+		struct css_task_iter	iter;
+	} procs;
+
+	struct {
+		struct cgroup_pidlist	*pidlist;
+	} procs1;
+};
+
+/*
+ * A cgroup can be associated with multiple css_sets as different tasks may
+ * belong to different cgroups on different hierarchies.  In the other
+ * direction, a css_set is naturally associated with multiple cgroups.
+ * This M:N relationship is represented by the following link structure
+ * which exists for each association and allows traversing the associations
+ * from both sides.
+ */
+struct cgrp_cset_link {
+	/* the cgroup and css_set this link associates */
+	struct cgroup		*cgrp;
+	struct css_set		*cset;
+
+	/* list of cgrp_cset_links anchored at cgrp->cset_links */
+	struct list_head	cset_link;
+
+	/* list of cgrp_cset_links anchored at css_set->cgrp_links */
+	struct list_head	cgrp_link;
+};
+
+/* used to track tasks and csets during migration */
+struct cgroup_taskset {
+	/* the src and dst cset list running through cset->mg_node */
+	struct list_head	src_csets;
+	struct list_head	dst_csets;
+
+	/* the number of tasks in the set */
+	int			nr_tasks;
+
+	/* the subsys currently being processed */
+	int			ssid;
+
+	/*
+	 * Fields for cgroup_taskset_*() iteration.
+	 *
+	 * Before migration is committed, the target migration tasks are on
+	 * ->mg_tasks of the csets on ->src_csets.  After, on ->mg_tasks of
+	 * the csets on ->dst_csets.  ->csets point to either ->src_csets
+	 * or ->dst_csets depending on whether migration is committed.
+	 *
+	 * ->cur_csets and ->cur_task point to the current task position
+	 * during iteration.
+	 */
+	struct list_head	*csets;
+	struct css_set		*cur_cset;
+	struct task_struct	*cur_task;
+};
+
+/* migration context also tracks preloading */
+struct cgroup_mgctx {
+	/*
+	 * Preloaded source and destination csets.  Used to guarantee
+	 * atomic success or failure on actual migration.
+	 */
+	struct list_head	preloaded_src_csets;
+	struct list_head	preloaded_dst_csets;
+
+	/* tasks and csets to migrate */
+	struct cgroup_taskset	tset;
+
+	/* subsystems affected by migration */
+	u16			ss_mask;
+};
+
+#define CGROUP_TASKSET_INIT(tset)						\
+{										\
+	.src_csets		= LIST_HEAD_INIT(tset.src_csets),		\
+	.dst_csets		= LIST_HEAD_INIT(tset.dst_csets),		\
+	.csets			= &tset.src_csets,				\
+}
+
+#define CGROUP_MGCTX_INIT(name)							\
+{										\
+	LIST_HEAD_INIT(name.preloaded_src_csets),				\
+	LIST_HEAD_INIT(name.preloaded_dst_csets),				\
+	CGROUP_TASKSET_INIT(name.tset),						\
+}
+
+#define DEFINE_CGROUP_MGCTX(name)						\
+	struct cgroup_mgctx name = CGROUP_MGCTX_INIT(name)
+
+struct cgroup_sb_opts {
+	u16 subsys_mask;
+	unsigned int flags;
+	char *release_agent;
+	bool cpuset_clone_children;
+	char *name;
+	/* User explicitly requested empty subsystem */
+	bool none;
+};
+
+extern struct mutex cgroup_mutex;
+extern spinlock_t css_set_lock;
+extern struct cgroup_subsys *cgroup_subsys[];
+extern struct list_head cgroup_roots;
+extern struct file_system_type cgroup_fs_type;
+
+/* iterate across the hierarchies */
+#define for_each_root(root)						\
+	list_for_each_entry((root), &cgroup_roots, root_list)
+
+/**
+ * for_each_subsys - iterate all enabled cgroup subsystems
+ * @ss: the iteration cursor
+ * @ssid: the index of @ss, CGROUP_SUBSYS_COUNT after reaching the end
+ */
+#define for_each_subsys(ss, ssid)					\
+	for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT &&		\
+	     (((ss) = cgroup_subsys[ssid]) || true); (ssid)++)
+
+static inline bool cgroup_is_dead(const struct cgroup *cgrp)
+{
+	return !(cgrp->self.flags & CSS_ONLINE);
+}
+
+static inline bool notify_on_release(const struct cgroup *cgrp)
+{
+	return test_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
+}
+
+void put_css_set_locked(struct css_set *cset);
+
+static inline void put_css_set(struct css_set *cset)
+{
+	unsigned long flags;
+
+	/*
+	 * Ensure that the refcount doesn't hit zero while any readers
+	 * can see it. Similar to atomic_dec_and_lock(), but for an
+	 * rwlock
+	 */
+	if (refcount_dec_not_one(&cset->refcount))
+		return;
+
+	spin_lock_irqsave(&css_set_lock, flags);
+	put_css_set_locked(cset);
+	spin_unlock_irqrestore(&css_set_lock, flags);
+}
+
+/*
+ * refcounted get/put for css_set objects
+ */
+static inline void get_css_set(struct css_set *cset)
+{
+	refcount_inc(&cset->refcount);
+}
+
+bool cgroup_ssid_enabled(int ssid);
+bool cgroup_on_dfl(const struct cgroup *cgrp);
+bool cgroup_is_thread_root(struct cgroup *cgrp);
+bool cgroup_is_threaded(struct cgroup *cgrp);
+
+struct cgroup_root *cgroup_root_from_kf(struct kernfs_root *kf_root);
+struct cgroup *task_cgroup_from_root(struct task_struct *task,
+				     struct cgroup_root *root);
+struct cgroup *cgroup_kn_lock_live(struct kernfs_node *kn, bool drain_offline);
+void cgroup_kn_unlock(struct kernfs_node *kn);
+int cgroup_path_ns_locked(struct cgroup *cgrp, char *buf, size_t buflen,
+			  struct cgroup_namespace *ns);
+
+void cgroup_free_root(struct cgroup_root *root);
+void init_cgroup_root(struct cgroup_root *root, struct cgroup_sb_opts *opts);
+int cgroup_setup_root(struct cgroup_root *root, u16 ss_mask, int ref_flags);
+int rebind_subsystems(struct cgroup_root *dst_root, u16 ss_mask);
+struct dentry *cgroup_do_mount(struct file_system_type *fs_type, int flags,
+			       struct cgroup_root *root, unsigned long magic,
+			       struct cgroup_namespace *ns);
+
+int cgroup_migrate_vet_dst(struct cgroup *dst_cgrp);
+void cgroup_migrate_finish(struct cgroup_mgctx *mgctx);
+void cgroup_migrate_add_src(struct css_set *src_cset, struct cgroup *dst_cgrp,
+			    struct cgroup_mgctx *mgctx);
+int cgroup_migrate_prepare_dst(struct cgroup_mgctx *mgctx);
+int cgroup_migrate(struct task_struct *leader, bool threadgroup,
+		   struct cgroup_mgctx *mgctx);
+
+int cgroup_attach_task(struct cgroup *dst_cgrp, struct task_struct *leader,
+		       bool threadgroup);
+struct task_struct *cgroup_procs_write_start(char *buf, bool threadgroup)
+	__acquires(&cgroup_threadgroup_rwsem);
+void cgroup_procs_write_finish(struct task_struct *task)
+	__releases(&cgroup_threadgroup_rwsem);
+
+void cgroup_lock_and_drain_offline(struct cgroup *cgrp);
+
+int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name, umode_t mode);
+int cgroup_rmdir(struct kernfs_node *kn);
+int cgroup_show_path(struct seq_file *sf, struct kernfs_node *kf_node,
+		     struct kernfs_root *kf_root);
+
+int cgroup_task_count(const struct cgroup *cgrp);
+
+/*
+ * rstat.c
+ */
+int cgroup_rstat_init(struct cgroup *cgrp);
+void cgroup_rstat_exit(struct cgroup *cgrp);
+void cgroup_rstat_boot(void);
+void cgroup_base_stat_cputime_show(struct seq_file *seq);
+
+/*
+ * namespace.c
+ */
+extern const struct proc_ns_operations cgroupns_operations;
+
+/*
+ * cgroup-v1.c
+ */
+extern struct cftype cgroup1_base_files[];
+extern struct kernfs_syscall_ops cgroup1_kf_syscall_ops;
+
+int proc_cgroupstats_show(struct seq_file *m, void *v);
+bool cgroup1_ssid_disabled(int ssid);
+void cgroup1_pidlist_destroy_all(struct cgroup *cgrp);
+void cgroup1_release_agent(struct work_struct *work);
+void cgroup1_check_for_release(struct cgroup *cgrp);
+struct dentry *cgroup1_mount(struct file_system_type *fs_type, int flags,
+			     void *data, unsigned long magic,
+			     struct cgroup_namespace *ns);
+
+#endif /* __CGROUP_INTERNAL_H */
diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c
new file mode 100644
index 000000000..616449762
--- /dev/null
+++ b/kernel/cgroup/cgroup-v1.c
@@ -0,0 +1,1340 @@
+#include "cgroup-internal.h"
+
+#include <linux/ctype.h>
+#include <linux/kmod.h>
+#include <linux/sort.h>
+#include <linux/delay.h>
+#include <linux/mm.h>
+#include <linux/sched/signal.h>
+#include <linux/sched/task.h>
+#include <linux/magic.h>
+#include <linux/slab.h>
+#include <linux/vmalloc.h>
+#include <linux/delayacct.h>
+#include <linux/pid_namespace.h>
+#include <linux/cgroupstats.h>
+
+#include <trace/events/cgroup.h>
+
+/*
+ * pidlists linger the following amount before being destroyed.  The goal
+ * is avoiding frequent destruction in the middle of consecutive read calls
+ * Expiring in the middle is a performance problem not a correctness one.
+ * 1 sec should be enough.
+ */
+#define CGROUP_PIDLIST_DESTROY_DELAY	HZ
+
+/* Controllers blocked by the commandline in v1 */
+static u16 cgroup_no_v1_mask;
+
+/*
+ * pidlist destructions need to be flushed on cgroup destruction.  Use a
+ * separate workqueue as flush domain.
+ */
+static struct workqueue_struct *cgroup_pidlist_destroy_wq;
+
+/*
+ * Protects cgroup_subsys->release_agent_path.  Modifying it also requires
+ * cgroup_mutex.  Reading requires either cgroup_mutex or this spinlock.
+ */
+static DEFINE_SPINLOCK(release_agent_path_lock);
+
+bool cgroup1_ssid_disabled(int ssid)
+{
+	return cgroup_no_v1_mask & (1 << ssid);
+}
+
+/**
+ * cgroup_attach_task_all - attach task 'tsk' to all cgroups of task 'from'
+ * @from: attach to all cgroups of a given task
+ * @tsk: the task to be attached
+ */
+int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk)
+{
+	struct cgroup_root *root;
+	int retval = 0;
+
+	mutex_lock(&cgroup_mutex);
+	percpu_down_write(&cgroup_threadgroup_rwsem);
+	for_each_root(root) {
+		struct cgroup *from_cgrp;
+
+		if (root == &cgrp_dfl_root)
+			continue;
+
+		spin_lock_irq(&css_set_lock);
+		from_cgrp = task_cgroup_from_root(from, root);
+		spin_unlock_irq(&css_set_lock);
+
+		retval = cgroup_attach_task(from_cgrp, tsk, false);
+		if (retval)
+			break;
+	}
+	percpu_up_write(&cgroup_threadgroup_rwsem);
+	mutex_unlock(&cgroup_mutex);
+
+	return retval;
+}
+EXPORT_SYMBOL_GPL(cgroup_attach_task_all);
+
+/**
+ * cgroup_trasnsfer_tasks - move tasks from one cgroup to another
+ * @to: cgroup to which the tasks will be moved
+ * @from: cgroup in which the tasks currently reside
+ *
+ * Locking rules between cgroup_post_fork() and the migration path
+ * guarantee that, if a task is forking while being migrated, the new child
+ * is guaranteed to be either visible in the source cgroup after the
+ * parent's migration is complete or put into the target cgroup.  No task
+ * can slip out of migration through forking.
+ */
+int cgroup_transfer_tasks(struct cgroup *to, struct cgroup *from)
+{
+	DEFINE_CGROUP_MGCTX(mgctx);
+	struct cgrp_cset_link *link;
+	struct css_task_iter it;
+	struct task_struct *task;
+	int ret;
+
+	if (cgroup_on_dfl(to))
+		return -EINVAL;
+
+	ret = cgroup_migrate_vet_dst(to);
+	if (ret)
+		return ret;
+
+	mutex_lock(&cgroup_mutex);
+
+	percpu_down_write(&cgroup_threadgroup_rwsem);
+
+	/* all tasks in @from are being moved, all csets are source */
+	spin_lock_irq(&css_set_lock);
+	list_for_each_entry(link, &from->cset_links, cset_link)
+		cgroup_migrate_add_src(link->cset, to, &mgctx);
+	spin_unlock_irq(&css_set_lock);
+
+	ret = cgroup_migrate_prepare_dst(&mgctx);
+	if (ret)
+		goto out_err;
+
+	/*
+	 * Migrate tasks one-by-one until @from is empty.  This fails iff
+	 * ->can_attach() fails.
+	 */
+	do {
+		css_task_iter_start(&from->self, 0, &it);
+
+		do {
+			task = css_task_iter_next(&it);
+		} while (task && (task->flags & PF_EXITING));
+
+		if (task)
+			get_task_struct(task);
+		css_task_iter_end(&it);
+
+		if (task) {
+			ret = cgroup_migrate(task, false, &mgctx);
+			if (!ret)
+				TRACE_CGROUP_PATH(transfer_tasks, to, task, false);
+			put_task_struct(task);
+		}
+	} while (task && !ret);
+out_err:
+	cgroup_migrate_finish(&mgctx);
+	percpu_up_write(&cgroup_threadgroup_rwsem);
+	mutex_unlock(&cgroup_mutex);
+	return ret;
+}
+
+/*
+ * Stuff for reading the 'tasks'/'procs' files.
+ *
+ * Reading this file can return large amounts of data if a cgroup has
+ * *lots* of attached tasks. So it may need several calls to read(),
+ * but we cannot guarantee that the information we produce is correct
+ * unless we produce it entirely atomically.
+ *
+ */
+
+/* which pidlist file are we talking about? */
+enum cgroup_filetype {
+	CGROUP_FILE_PROCS,
+	CGROUP_FILE_TASKS,
+};
+
+/*
+ * A pidlist is a list of pids that virtually represents the contents of one
+ * of the cgroup files ("procs" or "tasks"). We keep a list of such pidlists,
+ * a pair (one each for procs, tasks) for each pid namespace that's relevant
+ * to the cgroup.
+ */
+struct cgroup_pidlist {
+	/*
+	 * used to find which pidlist is wanted. doesn't change as long as
+	 * this particular list stays in the list.
+	*/
+	struct { enum cgroup_filetype type; struct pid_namespace *ns; } key;
+	/* array of xids */
+	pid_t *list;
+	/* how many elements the above list has */
+	int length;
+	/* each of these stored in a list by its cgroup */
+	struct list_head links;
+	/* pointer to the cgroup we belong to, for list removal purposes */
+	struct cgroup *owner;
+	/* for delayed destruction */
+	struct delayed_work destroy_dwork;
+};
+
+/*
+ * The following two functions "fix" the issue where there are more pids
+ * than kmalloc will give memory for; in such cases, we use vmalloc/vfree.
+ * TODO: replace with a kernel-wide solution to this problem
+ */
+#define PIDLIST_TOO_LARGE(c) ((c) * sizeof(pid_t) > (PAGE_SIZE * 2))
+static void *pidlist_allocate(int count)
+{
+	if (PIDLIST_TOO_LARGE(count))
+		return vmalloc(array_size(count, sizeof(pid_t)));
+	else
+		return kmalloc_array(count, sizeof(pid_t), GFP_KERNEL);
+}
+
+static void pidlist_free(void *p)
+{
+	kvfree(p);
+}
+
+/*
+ * Used to destroy all pidlists lingering waiting for destroy timer.  None
+ * should be left afterwards.
+ */
+void cgroup1_pidlist_destroy_all(struct cgroup *cgrp)
+{
+	struct cgroup_pidlist *l, *tmp_l;
+
+	mutex_lock(&cgrp->pidlist_mutex);
+	list_for_each_entry_safe(l, tmp_l, &cgrp->pidlists, links)
+		mod_delayed_work(cgroup_pidlist_destroy_wq, &l->destroy_dwork, 0);
+	mutex_unlock(&cgrp->pidlist_mutex);
+
+	flush_workqueue(cgroup_pidlist_destroy_wq);
+	BUG_ON(!list_empty(&cgrp->pidlists));
+}
+
+static void cgroup_pidlist_destroy_work_fn(struct work_struct *work)
+{
+	struct delayed_work *dwork = to_delayed_work(work);
+	struct cgroup_pidlist *l = container_of(dwork, struct cgroup_pidlist,
+						destroy_dwork);
+	struct cgroup_pidlist *tofree = NULL;
+
+	mutex_lock(&l->owner->pidlist_mutex);
+
+	/*
+	 * Destroy iff we didn't get queued again.  The state won't change
+	 * as destroy_dwork can only be queued while locked.
+	 */
+	if (!delayed_work_pending(dwork)) {
+		list_del(&l->links);
+		pidlist_free(l->list);
+		put_pid_ns(l->key.ns);
+		tofree = l;
+	}
+
+	mutex_unlock(&l->owner->pidlist_mutex);
+	kfree(tofree);
+}
+
+/*
+ * pidlist_uniq - given a kmalloc()ed list, strip out all duplicate entries
+ * Returns the number of unique elements.
+ */
+static int pidlist_uniq(pid_t *list, int length)
+{
+	int src, dest = 1;
+
+	/*
+	 * we presume the 0th element is unique, so i starts at 1. trivial
+	 * edge cases first; no work needs to be done for either
+	 */
+	if (length == 0 || length == 1)
+		return length;
+	/* src and dest walk down the list; dest counts unique elements */
+	for (src = 1; src < length; src++) {
+		/* find next unique element */
+		while (list[src] == list[src-1]) {
+			src++;
+			if (src == length)
+				goto after;
+		}
+		/* dest always points to where the next unique element goes */
+		list[dest] = list[src];
+		dest++;
+	}
+after:
+	return dest;
+}
+
+/*
+ * The two pid files - task and cgroup.procs - guaranteed that the result
+ * is sorted, which forced this whole pidlist fiasco.  As pid order is
+ * different per namespace, each namespace needs differently sorted list,
+ * making it impossible to use, for example, single rbtree of member tasks
+ * sorted by task pointer.  As pidlists can be fairly large, allocating one
+ * per open file is dangerous, so cgroup had to implement shared pool of
+ * pidlists keyed by cgroup and namespace.
+ */
+static int cmppid(const void *a, const void *b)
+{
+	return *(pid_t *)a - *(pid_t *)b;
+}
+
+static struct cgroup_pidlist *cgroup_pidlist_find(struct cgroup *cgrp,
+						  enum cgroup_filetype type)
+{
+	struct cgroup_pidlist *l;
+	/* don't need task_nsproxy() if we're looking at ourself */
+	struct pid_namespace *ns = task_active_pid_ns(current);
+
+	lockdep_assert_held(&cgrp->pidlist_mutex);
+
+	list_for_each_entry(l, &cgrp->pidlists, links)
+		if (l->key.type == type && l->key.ns == ns)
+			return l;
+	return NULL;
+}
+
+/*
+ * find the appropriate pidlist for our purpose (given procs vs tasks)
+ * returns with the lock on that pidlist already held, and takes care
+ * of the use count, or returns NULL with no locks held if we're out of
+ * memory.
+ */
+static struct cgroup_pidlist *cgroup_pidlist_find_create(struct cgroup *cgrp,
+						enum cgroup_filetype type)
+{
+	struct cgroup_pidlist *l;
+
+	lockdep_assert_held(&cgrp->pidlist_mutex);
+
+	l = cgroup_pidlist_find(cgrp, type);
+	if (l)
+		return l;
+
+	/* entry not found; create a new one */
+	l = kzalloc(sizeof(struct cgroup_pidlist), GFP_KERNEL);
+	if (!l)
+		return l;
+
+	INIT_DELAYED_WORK(&l->destroy_dwork, cgroup_pidlist_destroy_work_fn);
+	l->key.type = type;
+	/* don't need task_nsproxy() if we're looking at ourself */
+	l->key.ns = get_pid_ns(task_active_pid_ns(current));
+	l->owner = cgrp;
+	list_add(&l->links, &cgrp->pidlists);
+	return l;
+}
+
+/**
+ * cgroup_task_count - count the number of tasks in a cgroup.
+ * @cgrp: the cgroup in question
+ */
+int cgroup_task_count(const struct cgroup *cgrp)
+{
+	int count = 0;
+	struct cgrp_cset_link *link;
+
+	spin_lock_irq(&css_set_lock);
+	list_for_each_entry(link, &cgrp->cset_links, cset_link)
+		count += link->cset->nr_tasks;
+	spin_unlock_irq(&css_set_lock);
+	return count;
+}
+
+/*
+ * Load a cgroup's pidarray with either procs' tgids or tasks' pids
+ */
+static int pidlist_array_load(struct cgroup *cgrp, enum cgroup_filetype type,
+			      struct cgroup_pidlist **lp)
+{
+	pid_t *array;
+	int length;
+	int pid, n = 0; /* used for populating the array */
+	struct css_task_iter it;
+	struct task_struct *tsk;
+	struct cgroup_pidlist *l;
+
+	lockdep_assert_held(&cgrp->pidlist_mutex);
+
+	/*
+	 * If cgroup gets more users after we read count, we won't have
+	 * enough space - tough.  This race is indistinguishable to the
+	 * caller from the case that the additional cgroup users didn't
+	 * show up until sometime later on.
+	 */
+	length = cgroup_task_count(cgrp);
+	array = pidlist_allocate(length);
+	if (!array)
+		return -ENOMEM;
+	/* now, populate the array */
+	css_task_iter_start(&cgrp->self, 0, &it);
+	while ((tsk = css_task_iter_next(&it))) {
+		if (unlikely(n == length))
+			break;
+		/* get tgid or pid for procs or tasks file respectively */
+		if (type == CGROUP_FILE_PROCS)
+			pid = task_tgid_vnr(tsk);
+		else
+			pid = task_pid_vnr(tsk);
+		if (pid > 0) /* make sure to only use valid results */
+			array[n++] = pid;
+	}
+	css_task_iter_end(&it);
+	length = n;
+	/* now sort & (if procs) strip out duplicates */
+	sort(array, length, sizeof(pid_t), cmppid, NULL);
+	if (type == CGROUP_FILE_PROCS)
+		length = pidlist_uniq(array, length);
+
+	l = cgroup_pidlist_find_create(cgrp, type);
+	if (!l) {
+		pidlist_free(array);
+		return -ENOMEM;
+	}
+
+	/* store array, freeing old if necessary */
+	pidlist_free(l->list);
+	l->list = array;
+	l->length = length;
+	*lp = l;
+	return 0;
+}
+
+/*
+ * seq_file methods for the tasks/procs files. The seq_file position is the
+ * next pid to display; the seq_file iterator is a pointer to the pid
+ * in the cgroup->l->list array.
+ */
+
+static void *cgroup_pidlist_start(struct seq_file *s, loff_t *pos)
+{
+	/*
+	 * Initially we receive a position value that corresponds to
+	 * one more than the last pid shown (or 0 on the first call or
+	 * after a seek to the start). Use a binary-search to find the
+	 * next pid to display, if any
+	 */
+	struct kernfs_open_file *of = s->private;
+	struct cgroup_file_ctx *ctx = of->priv;
+	struct cgroup *cgrp = seq_css(s)->cgroup;
+	struct cgroup_pidlist *l;
+	enum cgroup_filetype type = seq_cft(s)->private;
+	int index = 0, pid = *pos;
+	int *iter, ret;
+
+	mutex_lock(&cgrp->pidlist_mutex);
+
+	/*
+	 * !NULL @ctx->procs1.pidlist indicates that this isn't the first
+	 * start() after open. If the matching pidlist is around, we can use
+	 * that. Look for it. Note that @ctx->procs1.pidlist can't be used
+	 * directly. It could already have been destroyed.
+	 */
+	if (ctx->procs1.pidlist)
+		ctx->procs1.pidlist = cgroup_pidlist_find(cgrp, type);
+
+	/*
+	 * Either this is the first start() after open or the matching
+	 * pidlist has been destroyed inbetween.  Create a new one.
+	 */
+	if (!ctx->procs1.pidlist) {
+		ret = pidlist_array_load(cgrp, type, &ctx->procs1.pidlist);
+		if (ret)
+			return ERR_PTR(ret);
+	}
+	l = ctx->procs1.pidlist;
+
+	if (pid) {
+		int end = l->length;
+
+		while (index < end) {
+			int mid = (index + end) / 2;
+			if (l->list[mid] == pid) {
+				index = mid;
+				break;
+			} else if (l->list[mid] <= pid)
+				index = mid + 1;
+			else
+				end = mid;
+		}
+	}
+	/* If we're off the end of the array, we're done */
+	if (index >= l->length)
+		return NULL;
+	/* Update the abstract position to be the actual pid that we found */
+	iter = l->list + index;
+	*pos = *iter;
+	return iter;
+}
+
+static void cgroup_pidlist_stop(struct seq_file *s, void *v)
+{
+	struct kernfs_open_file *of = s->private;
+	struct cgroup_file_ctx *ctx = of->priv;
+	struct cgroup_pidlist *l = ctx->procs1.pidlist;
+
+	if (l)
+		mod_delayed_work(cgroup_pidlist_destroy_wq, &l->destroy_dwork,
+				 CGROUP_PIDLIST_DESTROY_DELAY);
+	mutex_unlock(&seq_css(s)->cgroup->pidlist_mutex);
+}
+
+static void *cgroup_pidlist_next(struct seq_file *s, void *v, loff_t *pos)
+{
+	struct kernfs_open_file *of = s->private;
+	struct cgroup_file_ctx *ctx = of->priv;
+	struct cgroup_pidlist *l = ctx->procs1.pidlist;
+	pid_t *p = v;
+	pid_t *end = l->list + l->length;
+	/*
+	 * Advance to the next pid in the array. If this goes off the
+	 * end, we're done
+	 */
+	p++;
+	if (p >= end) {
+		(*pos)++;
+		return NULL;
+	} else {
+		*pos = *p;
+		return p;
+	}
+}
+
+static int cgroup_pidlist_show(struct seq_file *s, void *v)
+{
+	seq_printf(s, "%d\n", *(int *)v);
+
+	return 0;
+}
+
+static ssize_t __cgroup1_procs_write(struct kernfs_open_file *of,
+				     char *buf, size_t nbytes, loff_t off,
+				     bool threadgroup)
+{
+	struct cgroup *cgrp;
+	struct task_struct *task;
+	const struct cred *cred, *tcred;
+	ssize_t ret;
+
+	cgrp = cgroup_kn_lock_live(of->kn, false);
+	if (!cgrp)
+		return -ENODEV;
+
+	task = cgroup_procs_write_start(buf, threadgroup);
+	ret = PTR_ERR_OR_ZERO(task);
+	if (ret)
+		goto out_unlock;
+
+	/*
+	 * Even if we're attaching all tasks in the thread group, we only need
+	 * to check permissions on one of them. Check permissions using the
+	 * credentials from file open to protect against inherited fd attacks.
+	 */
+	cred = of->file->f_cred;
+	tcred = get_task_cred(task);
+	if (!uid_eq(cred->euid, GLOBAL_ROOT_UID) &&
+	    !uid_eq(cred->euid, tcred->uid) &&
+	    !uid_eq(cred->euid, tcred->suid))
+		ret = -EACCES;
+	put_cred(tcred);
+	if (ret)
+		goto out_finish;
+
+	ret = cgroup_attach_task(cgrp, task, threadgroup);
+
+out_finish:
+	cgroup_procs_write_finish(task);
+out_unlock:
+	cgroup_kn_unlock(of->kn);
+
+	return ret ?: nbytes;
+}
+
+static ssize_t cgroup1_procs_write(struct kernfs_open_file *of,
+				   char *buf, size_t nbytes, loff_t off)
+{
+	return __cgroup1_procs_write(of, buf, nbytes, off, true);
+}
+
+static ssize_t cgroup1_tasks_write(struct kernfs_open_file *of,
+				   char *buf, size_t nbytes, loff_t off)
+{
+	return __cgroup1_procs_write(of, buf, nbytes, off, false);
+}
+
+static ssize_t cgroup_release_agent_write(struct kernfs_open_file *of,
+					  char *buf, size_t nbytes, loff_t off)
+{
+	struct cgroup *cgrp;
+
+	BUILD_BUG_ON(sizeof(cgrp->root->release_agent_path) < PATH_MAX);
+
+	/*
+	 * Release agent gets called with all capabilities,
+	 * require capabilities to set release agent.
+	 */
+	if ((of->file->f_cred->user_ns != &init_user_ns) ||
+	    !capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
+	cgrp = cgroup_kn_lock_live(of->kn, false);
+	if (!cgrp)
+		return -ENODEV;
+	spin_lock(&release_agent_path_lock);
+	strlcpy(cgrp->root->release_agent_path, strstrip(buf),
+		sizeof(cgrp->root->release_agent_path));
+	spin_unlock(&release_agent_path_lock);
+	cgroup_kn_unlock(of->kn);
+	return nbytes;
+}
+
+static int cgroup_release_agent_show(struct seq_file *seq, void *v)
+{
+	struct cgroup *cgrp = seq_css(seq)->cgroup;
+
+	spin_lock(&release_agent_path_lock);
+	seq_puts(seq, cgrp->root->release_agent_path);
+	spin_unlock(&release_agent_path_lock);
+	seq_putc(seq, '\n');
+	return 0;
+}
+
+static int cgroup_sane_behavior_show(struct seq_file *seq, void *v)
+{
+	seq_puts(seq, "0\n");
+	return 0;
+}
+
+static u64 cgroup_read_notify_on_release(struct cgroup_subsys_state *css,
+					 struct cftype *cft)
+{
+	return notify_on_release(css->cgroup);
+}
+
+static int cgroup_write_notify_on_release(struct cgroup_subsys_state *css,
+					  struct cftype *cft, u64 val)
+{
+	if (val)
+		set_bit(CGRP_NOTIFY_ON_RELEASE, &css->cgroup->flags);
+	else
+		clear_bit(CGRP_NOTIFY_ON_RELEASE, &css->cgroup->flags);
+	return 0;
+}
+
+static u64 cgroup_clone_children_read(struct cgroup_subsys_state *css,
+				      struct cftype *cft)
+{
+	return test_bit(CGRP_CPUSET_CLONE_CHILDREN, &css->cgroup->flags);
+}
+
+static int cgroup_clone_children_write(struct cgroup_subsys_state *css,
+				       struct cftype *cft, u64 val)
+{
+	if (val)
+		set_bit(CGRP_CPUSET_CLONE_CHILDREN, &css->cgroup->flags);
+	else
+		clear_bit(CGRP_CPUSET_CLONE_CHILDREN, &css->cgroup->flags);
+	return 0;
+}
+
+/* cgroup core interface files for the legacy hierarchies */
+struct cftype cgroup1_base_files[] = {
+	{
+		.name = "cgroup.procs",
+		.seq_start = cgroup_pidlist_start,
+		.seq_next = cgroup_pidlist_next,
+		.seq_stop = cgroup_pidlist_stop,
+		.seq_show = cgroup_pidlist_show,
+		.private = CGROUP_FILE_PROCS,
+		.write = cgroup1_procs_write,
+	},
+	{
+		.name = "cgroup.clone_children",
+		.read_u64 = cgroup_clone_children_read,
+		.write_u64 = cgroup_clone_children_write,
+	},
+	{
+		.name = "cgroup.sane_behavior",
+		.flags = CFTYPE_ONLY_ON_ROOT,
+		.seq_show = cgroup_sane_behavior_show,
+	},
+	{
+		.name = "tasks",
+		.seq_start = cgroup_pidlist_start,
+		.seq_next = cgroup_pidlist_next,
+		.seq_stop = cgroup_pidlist_stop,
+		.seq_show = cgroup_pidlist_show,
+		.private = CGROUP_FILE_TASKS,
+		.write = cgroup1_tasks_write,
+	},
+	{
+		.name = "notify_on_release",
+		.read_u64 = cgroup_read_notify_on_release,
+		.write_u64 = cgroup_write_notify_on_release,
+	},
+	{
+		.name = "release_agent",
+		.flags = CFTYPE_ONLY_ON_ROOT,
+		.seq_show = cgroup_release_agent_show,
+		.write = cgroup_release_agent_write,
+		.max_write_len = PATH_MAX - 1,
+	},
+	{ }	/* terminate */
+};
+
+/* Display information about each subsystem and each hierarchy */
+int proc_cgroupstats_show(struct seq_file *m, void *v)
+{
+	struct cgroup_subsys *ss;
+	int i;
+
+	seq_puts(m, "#subsys_name\thierarchy\tnum_cgroups\tenabled\n");
+	/*
+	 * ideally we don't want subsystems moving around while we do this.
+	 * cgroup_mutex is also necessary to guarantee an atomic snapshot of
+	 * subsys/hierarchy state.
+	 */
+	mutex_lock(&cgroup_mutex);
+
+	for_each_subsys(ss, i)
+		seq_printf(m, "%s\t%d\t%d\t%d\n",
+			   ss->legacy_name, ss->root->hierarchy_id,
+			   atomic_read(&ss->root->nr_cgrps),
+			   cgroup_ssid_enabled(i));
+
+	mutex_unlock(&cgroup_mutex);
+	return 0;
+}
+
+/**
+ * cgroupstats_build - build and fill cgroupstats
+ * @stats: cgroupstats to fill information into
+ * @dentry: A dentry entry belonging to the cgroup for which stats have
+ * been requested.
+ *
+ * Build and fill cgroupstats so that taskstats can export it to user
+ * space.
+ */
+int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry)
+{
+	struct kernfs_node *kn = kernfs_node_from_dentry(dentry);
+	struct cgroup *cgrp;
+	struct css_task_iter it;
+	struct task_struct *tsk;
+
+	/* it should be kernfs_node belonging to cgroupfs and is a directory */
+	if (dentry->d_sb->s_type != &cgroup_fs_type || !kn ||
+	    kernfs_type(kn) != KERNFS_DIR)
+		return -EINVAL;
+
+	mutex_lock(&cgroup_mutex);
+
+	/*
+	 * We aren't being called from kernfs and there's no guarantee on
+	 * @kn->priv's validity.  For this and css_tryget_online_from_dir(),
+	 * @kn->priv is RCU safe.  Let's do the RCU dancing.
+	 */
+	rcu_read_lock();
+	cgrp = rcu_dereference(*(void __rcu __force **)&kn->priv);
+	if (!cgrp || cgroup_is_dead(cgrp)) {
+		rcu_read_unlock();
+		mutex_unlock(&cgroup_mutex);
+		return -ENOENT;
+	}
+	rcu_read_unlock();
+
+	css_task_iter_start(&cgrp->self, 0, &it);
+	while ((tsk = css_task_iter_next(&it))) {
+		switch (tsk->state) {
+		case TASK_RUNNING:
+			stats->nr_running++;
+			break;
+		case TASK_INTERRUPTIBLE:
+			stats->nr_sleeping++;
+			break;
+		case TASK_UNINTERRUPTIBLE:
+			stats->nr_uninterruptible++;
+			break;
+		case TASK_STOPPED:
+			stats->nr_stopped++;
+			break;
+		default:
+			if (delayacct_is_task_waiting_on_io(tsk))
+				stats->nr_io_wait++;
+			break;
+		}
+	}
+	css_task_iter_end(&it);
+
+	mutex_unlock(&cgroup_mutex);
+	return 0;
+}
+
+void cgroup1_check_for_release(struct cgroup *cgrp)
+{
+	if (notify_on_release(cgrp) && !cgroup_is_populated(cgrp) &&
+	    !css_has_online_children(&cgrp->self) && !cgroup_is_dead(cgrp))
+		schedule_work(&cgrp->release_agent_work);
+}
+
+/*
+ * Notify userspace when a cgroup is released, by running the
+ * configured release agent with the name of the cgroup (path
+ * relative to the root of cgroup file system) as the argument.
+ *
+ * Most likely, this user command will try to rmdir this cgroup.
+ *
+ * This races with the possibility that some other task will be
+ * attached to this cgroup before it is removed, or that some other
+ * user task will 'mkdir' a child cgroup of this cgroup.  That's ok.
+ * The presumed 'rmdir' will fail quietly if this cgroup is no longer
+ * unused, and this cgroup will be reprieved from its death sentence,
+ * to continue to serve a useful existence.  Next time it's released,
+ * we will get notified again, if it still has 'notify_on_release' set.
+ *
+ * The final arg to call_usermodehelper() is UMH_WAIT_EXEC, which
+ * means only wait until the task is successfully execve()'d.  The
+ * separate release agent task is forked by call_usermodehelper(),
+ * then control in this thread returns here, without waiting for the
+ * release agent task.  We don't bother to wait because the caller of
+ * this routine has no use for the exit status of the release agent
+ * task, so no sense holding our caller up for that.
+ */
+void cgroup1_release_agent(struct work_struct *work)
+{
+	struct cgroup *cgrp =
+		container_of(work, struct cgroup, release_agent_work);
+	char *pathbuf = NULL, *agentbuf = NULL;
+	char *argv[3], *envp[3];
+	int ret;
+
+	mutex_lock(&cgroup_mutex);
+
+	pathbuf = kmalloc(PATH_MAX, GFP_KERNEL);
+	agentbuf = kstrdup(cgrp->root->release_agent_path, GFP_KERNEL);
+	if (!pathbuf || !agentbuf || !strlen(agentbuf))
+		goto out;
+
+	spin_lock_irq(&css_set_lock);
+	ret = cgroup_path_ns_locked(cgrp, pathbuf, PATH_MAX, &init_cgroup_ns);
+	spin_unlock_irq(&css_set_lock);
+	if (ret < 0 || ret >= PATH_MAX)
+		goto out;
+
+	argv[0] = agentbuf;
+	argv[1] = pathbuf;
+	argv[2] = NULL;
+
+	/* minimal command environment */
+	envp[0] = "HOME=/";
+	envp[1] = "PATH=/sbin:/bin:/usr/sbin:/usr/bin";
+	envp[2] = NULL;
+
+	mutex_unlock(&cgroup_mutex);
+	call_usermodehelper(argv[0], argv, envp, UMH_WAIT_EXEC);
+	goto out_free;
+out:
+	mutex_unlock(&cgroup_mutex);
+out_free:
+	kfree(agentbuf);
+	kfree(pathbuf);
+}
+
+/*
+ * cgroup_rename - Only allow simple rename of directories in place.
+ */
+static int cgroup1_rename(struct kernfs_node *kn, struct kernfs_node *new_parent,
+			  const char *new_name_str)
+{
+	struct cgroup *cgrp = kn->priv;
+	int ret;
+
+	/* do not accept '\n' to prevent making /proc/<pid>/cgroup unparsable */
+	if (strchr(new_name_str, '\n'))
+		return -EINVAL;
+
+	if (kernfs_type(kn) != KERNFS_DIR)
+		return -ENOTDIR;
+	if (kn->parent != new_parent)
+		return -EIO;
+
+	/*
+	 * We're gonna grab cgroup_mutex which nests outside kernfs
+	 * active_ref.  kernfs_rename() doesn't require active_ref
+	 * protection.  Break them before grabbing cgroup_mutex.
+	 */
+	kernfs_break_active_protection(new_parent);
+	kernfs_break_active_protection(kn);
+
+	mutex_lock(&cgroup_mutex);
+
+	ret = kernfs_rename(kn, new_parent, new_name_str);
+	if (!ret)
+		TRACE_CGROUP_PATH(rename, cgrp);
+
+	mutex_unlock(&cgroup_mutex);
+
+	kernfs_unbreak_active_protection(kn);
+	kernfs_unbreak_active_protection(new_parent);
+	return ret;
+}
+
+static int cgroup1_show_options(struct seq_file *seq, struct kernfs_root *kf_root)
+{
+	struct cgroup_root *root = cgroup_root_from_kf(kf_root);
+	struct cgroup_subsys *ss;
+	int ssid;
+
+	for_each_subsys(ss, ssid)
+		if (root->subsys_mask & (1 << ssid))
+			seq_show_option(seq, ss->legacy_name, NULL);
+	if (root->flags & CGRP_ROOT_NOPREFIX)
+		seq_puts(seq, ",noprefix");
+	if (root->flags & CGRP_ROOT_XATTR)
+		seq_puts(seq, ",xattr");
+	if (root->flags & CGRP_ROOT_CPUSET_V2_MODE)
+		seq_puts(seq, ",cpuset_v2_mode");
+
+	spin_lock(&release_agent_path_lock);
+	if (strlen(root->release_agent_path))
+		seq_show_option(seq, "release_agent",
+				root->release_agent_path);
+	spin_unlock(&release_agent_path_lock);
+
+	if (test_bit(CGRP_CPUSET_CLONE_CHILDREN, &root->cgrp.flags))
+		seq_puts(seq, ",clone_children");
+	if (strlen(root->name))
+		seq_show_option(seq, "name", root->name);
+	return 0;
+}
+
+static int parse_cgroupfs_options(char *data, struct cgroup_sb_opts *opts)
+{
+	char *token, *o = data;
+	bool all_ss = false, one_ss = false;
+	u16 mask = U16_MAX;
+	struct cgroup_subsys *ss;
+	int nr_opts = 0;
+	int i;
+
+#ifdef CONFIG_CPUSETS
+	mask = ~((u16)1 << cpuset_cgrp_id);
+#endif
+
+	memset(opts, 0, sizeof(*opts));
+
+	while ((token = strsep(&o, ",")) != NULL) {
+		nr_opts++;
+
+		if (!*token)
+			return -EINVAL;
+		if (!strcmp(token, "none")) {
+			/* Explicitly have no subsystems */
+			opts->none = true;
+			continue;
+		}
+		if (!strcmp(token, "all")) {
+			/* Mutually exclusive option 'all' + subsystem name */
+			if (one_ss)
+				return -EINVAL;
+			all_ss = true;
+			continue;
+		}
+		if (!strcmp(token, "noprefix")) {
+			opts->flags |= CGRP_ROOT_NOPREFIX;
+			continue;
+		}
+		if (!strcmp(token, "clone_children")) {
+			opts->cpuset_clone_children = true;
+			continue;
+		}
+		if (!strcmp(token, "cpuset_v2_mode")) {
+			opts->flags |= CGRP_ROOT_CPUSET_V2_MODE;
+			continue;
+		}
+		if (!strcmp(token, "xattr")) {
+			opts->flags |= CGRP_ROOT_XATTR;
+			continue;
+		}
+		if (!strncmp(token, "release_agent=", 14)) {
+			/* Specifying two release agents is forbidden */
+			if (opts->release_agent)
+				return -EINVAL;
+			opts->release_agent =
+				kstrndup(token + 14, PATH_MAX - 1, GFP_KERNEL);
+			if (!opts->release_agent)
+				return -ENOMEM;
+			continue;
+		}
+		if (!strncmp(token, "name=", 5)) {
+			const char *name = token + 5;
+			/* Can't specify an empty name */
+			if (!strlen(name))
+				return -EINVAL;
+			/* Must match [\w.-]+ */
+			for (i = 0; i < strlen(name); i++) {
+				char c = name[i];
+				if (isalnum(c))
+					continue;
+				if ((c == '.') || (c == '-') || (c == '_'))
+					continue;
+				return -EINVAL;
+			}
+			/* Specifying two names is forbidden */
+			if (opts->name)
+				return -EINVAL;
+			opts->name = kstrndup(name,
+					      MAX_CGROUP_ROOT_NAMELEN - 1,
+					      GFP_KERNEL);
+			if (!opts->name)
+				return -ENOMEM;
+
+			continue;
+		}
+
+		for_each_subsys(ss, i) {
+			if (strcmp(token, ss->legacy_name))
+				continue;
+			if (!cgroup_ssid_enabled(i))
+				continue;
+			if (cgroup1_ssid_disabled(i))
+				continue;
+
+			/* Mutually exclusive option 'all' + subsystem name */
+			if (all_ss)
+				return -EINVAL;
+			opts->subsys_mask |= (1 << i);
+			one_ss = true;
+
+			break;
+		}
+		if (i == CGROUP_SUBSYS_COUNT)
+			return -ENOENT;
+	}
+
+	/*
+	 * If the 'all' option was specified select all the subsystems,
+	 * otherwise if 'none', 'name=' and a subsystem name options were
+	 * not specified, let's default to 'all'
+	 */
+	if (all_ss || (!one_ss && !opts->none && !opts->name))
+		for_each_subsys(ss, i)
+			if (cgroup_ssid_enabled(i) && !cgroup1_ssid_disabled(i))
+				opts->subsys_mask |= (1 << i);
+
+	/*
+	 * We either have to specify by name or by subsystems. (So all
+	 * empty hierarchies must have a name).
+	 */
+	if (!opts->subsys_mask && !opts->name)
+		return -EINVAL;
+
+	/*
+	 * Option noprefix was introduced just for backward compatibility
+	 * with the old cpuset, so we allow noprefix only if mounting just
+	 * the cpuset subsystem.
+	 */
+	if ((opts->flags & CGRP_ROOT_NOPREFIX) && (opts->subsys_mask & mask))
+		return -EINVAL;
+
+	/* Can't specify "none" and some subsystems */
+	if (opts->subsys_mask && opts->none)
+		return -EINVAL;
+
+	return 0;
+}
+
+static int cgroup1_remount(struct kernfs_root *kf_root, int *flags, char *data)
+{
+	int ret = 0;
+	struct cgroup_root *root = cgroup_root_from_kf(kf_root);
+	struct cgroup_namespace *ns = current->nsproxy->cgroup_ns;
+	struct cgroup_sb_opts opts;
+	u16 added_mask, removed_mask;
+
+	cgroup_lock_and_drain_offline(&cgrp_dfl_root.cgrp);
+
+	/* See what subsystems are wanted */
+	ret = parse_cgroupfs_options(data, &opts);
+	if (ret)
+		goto out_unlock;
+
+	if (opts.subsys_mask != root->subsys_mask || opts.release_agent)
+		pr_warn("option changes via remount are deprecated (pid=%d comm=%s)\n",
+			task_tgid_nr(current), current->comm);
+	/* See cgroup1_mount release_agent handling */
+	if (opts.release_agent &&
+	    ((ns->user_ns != &init_user_ns) || !capable(CAP_SYS_ADMIN))) {
+		ret = -EINVAL;
+		goto out_unlock;
+	}
+
+	added_mask = opts.subsys_mask & ~root->subsys_mask;
+	removed_mask = root->subsys_mask & ~opts.subsys_mask;
+
+	/* Don't allow flags or name to change at remount */
+	if ((opts.flags ^ root->flags) ||
+	    (opts.name && strcmp(opts.name, root->name))) {
+		pr_err("option or name mismatch, new: 0x%x \"%s\", old: 0x%x \"%s\"\n",
+		       opts.flags, opts.name ?: "", root->flags, root->name);
+		ret = -EINVAL;
+		goto out_unlock;
+	}
+
+	/* remounting is not allowed for populated hierarchies */
+	if (!list_empty(&root->cgrp.self.children)) {
+		ret = -EBUSY;
+		goto out_unlock;
+	}
+
+	ret = rebind_subsystems(root, added_mask);
+	if (ret)
+		goto out_unlock;
+
+	WARN_ON(rebind_subsystems(&cgrp_dfl_root, removed_mask));
+
+	if (opts.release_agent) {
+		spin_lock(&release_agent_path_lock);
+		strcpy(root->release_agent_path, opts.release_agent);
+		spin_unlock(&release_agent_path_lock);
+	}
+
+	trace_cgroup_remount(root);
+
+ out_unlock:
+	kfree(opts.release_agent);
+	kfree(opts.name);
+	mutex_unlock(&cgroup_mutex);
+	return ret;
+}
+
+struct kernfs_syscall_ops cgroup1_kf_syscall_ops = {
+	.rename			= cgroup1_rename,
+	.show_options		= cgroup1_show_options,
+	.remount_fs		= cgroup1_remount,
+	.mkdir			= cgroup_mkdir,
+	.rmdir			= cgroup_rmdir,
+	.show_path		= cgroup_show_path,
+};
+
+struct dentry *cgroup1_mount(struct file_system_type *fs_type, int flags,
+			     void *data, unsigned long magic,
+			     struct cgroup_namespace *ns)
+{
+	struct super_block *pinned_sb = NULL;
+	struct cgroup_sb_opts opts;
+	struct cgroup_root *root;
+	struct cgroup_subsys *ss;
+	struct dentry *dentry;
+	int i, ret;
+	bool new_root = false;
+
+	cgroup_lock_and_drain_offline(&cgrp_dfl_root.cgrp);
+
+	/* First find the desired set of subsystems */
+	ret = parse_cgroupfs_options(data, &opts);
+	if (ret)
+		goto out_unlock;
+
+	/*
+	 * Destruction of cgroup root is asynchronous, so subsystems may
+	 * still be dying after the previous unmount.  Let's drain the
+	 * dying subsystems.  We just need to ensure that the ones
+	 * unmounted previously finish dying and don't care about new ones
+	 * starting.  Testing ref liveliness is good enough.
+	 */
+	for_each_subsys(ss, i) {
+		if (!(opts.subsys_mask & (1 << i)) ||
+		    ss->root == &cgrp_dfl_root)
+			continue;
+
+		if (!percpu_ref_tryget_live(&ss->root->cgrp.self.refcnt)) {
+			mutex_unlock(&cgroup_mutex);
+			msleep(10);
+			ret = restart_syscall();
+			goto out_free;
+		}
+		cgroup_put(&ss->root->cgrp);
+	}
+
+	for_each_root(root) {
+		bool name_match = false;
+
+		if (root == &cgrp_dfl_root)
+			continue;
+
+		/*
+		 * If we asked for a name then it must match.  Also, if
+		 * name matches but sybsys_mask doesn't, we should fail.
+		 * Remember whether name matched.
+		 */
+		if (opts.name) {
+			if (strcmp(opts.name, root->name))
+				continue;
+			name_match = true;
+		}
+
+		/*
+		 * If we asked for subsystems (or explicitly for no
+		 * subsystems) then they must match.
+		 */
+		if ((opts.subsys_mask || opts.none) &&
+		    (opts.subsys_mask != root->subsys_mask)) {
+			if (!name_match)
+				continue;
+			ret = -EBUSY;
+			goto out_unlock;
+		}
+
+		if (root->flags ^ opts.flags)
+			pr_warn("new mount options do not match the existing superblock, will be ignored\n");
+
+		/*
+		 * We want to reuse @root whose lifetime is governed by its
+		 * ->cgrp.  Let's check whether @root is alive and keep it
+		 * that way.  As cgroup_kill_sb() can happen anytime, we
+		 * want to block it by pinning the sb so that @root doesn't
+		 * get killed before mount is complete.
+		 *
+		 * With the sb pinned, tryget_live can reliably indicate
+		 * whether @root can be reused.  If it's being killed,
+		 * drain it.  We can use wait_queue for the wait but this
+		 * path is super cold.  Let's just sleep a bit and retry.
+		 */
+		pinned_sb = kernfs_pin_sb(root->kf_root, NULL);
+		if (IS_ERR(pinned_sb) ||
+		    !percpu_ref_tryget_live(&root->cgrp.self.refcnt)) {
+			mutex_unlock(&cgroup_mutex);
+			if (!IS_ERR_OR_NULL(pinned_sb))
+				deactivate_super(pinned_sb);
+			msleep(10);
+			ret = restart_syscall();
+			goto out_free;
+		}
+
+		ret = 0;
+		goto out_unlock;
+	}
+
+	/*
+	 * No such thing, create a new one.  name= matching without subsys
+	 * specification is allowed for already existing hierarchies but we
+	 * can't create new one without subsys specification.
+	 */
+	if (!opts.subsys_mask && !opts.none) {
+		ret = -EINVAL;
+		goto out_unlock;
+	}
+
+	/* Hierarchies may only be created in the initial cgroup namespace. */
+	if (ns != &init_cgroup_ns) {
+		ret = -EPERM;
+		goto out_unlock;
+	}
+	/*
+	 * Release agent gets called with all capabilities,
+	 * require capabilities to set release agent.
+	 */
+	if (opts.release_agent &&
+	    ((ns->user_ns != &init_user_ns) || !capable(CAP_SYS_ADMIN))) {
+		ret = -EINVAL;
+		goto out_unlock;
+	}
+
+	root = kzalloc(sizeof(*root), GFP_KERNEL);
+	if (!root) {
+		ret = -ENOMEM;
+		goto out_unlock;
+	}
+	new_root = true;
+
+	init_cgroup_root(root, &opts);
+
+	ret = cgroup_setup_root(root, opts.subsys_mask, PERCPU_REF_INIT_DEAD);
+	if (ret)
+		cgroup_free_root(root);
+
+out_unlock:
+	mutex_unlock(&cgroup_mutex);
+out_free:
+	kfree(opts.release_agent);
+	kfree(opts.name);
+
+	if (ret)
+		return ERR_PTR(ret);
+
+	dentry = cgroup_do_mount(&cgroup_fs_type, flags, root,
+				 CGROUP_SUPER_MAGIC, ns);
+
+	/*
+	 * There's a race window after we release cgroup_mutex and before
+	 * allocating a superblock. Make sure a concurrent process won't
+	 * be able to re-use the root during this window by delaying the
+	 * initialization of root refcnt.
+	 */
+	if (new_root) {
+		mutex_lock(&cgroup_mutex);
+		percpu_ref_reinit(&root->cgrp.self.refcnt);
+		mutex_unlock(&cgroup_mutex);
+	}
+
+	/*
+	 * If @pinned_sb, we're reusing an existing root and holding an
+	 * extra ref on its sb.  Mount is complete.  Put the extra ref.
+	 */
+	if (pinned_sb)
+		deactivate_super(pinned_sb);
+
+	return dentry;
+}
+
+static int __init cgroup1_wq_init(void)
+{
+	/*
+	 * Used to destroy pidlists and separate to serve as flush domain.
+	 * Cap @max_active to 1 too.
+	 */
+	cgroup_pidlist_destroy_wq = alloc_workqueue("cgroup_pidlist_destroy",
+						    0, 1);
+	BUG_ON(!cgroup_pidlist_destroy_wq);
+	return 0;
+}
+core_initcall(cgroup1_wq_init);
+
+static int __init cgroup_no_v1(char *str)
+{
+	struct cgroup_subsys *ss;
+	char *token;
+	int i;
+
+	while ((token = strsep(&str, ",")) != NULL) {
+		if (!*token)
+			continue;
+
+		if (!strcmp(token, "all")) {
+			cgroup_no_v1_mask = U16_MAX;
+			break;
+		}
+
+		for_each_subsys(ss, i) {
+			if (strcmp(token, ss->name) &&
+			    strcmp(token, ss->legacy_name))
+				continue;
+
+			cgroup_no_v1_mask |= 1 << i;
+		}
+	}
+	return 1;
+}
+__setup("cgroup_no_v1=", cgroup_no_v1);
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
new file mode 100644
index 000000000..4e8284d8c
--- /dev/null
+++ b/kernel/cgroup/cgroup.c
@@ -0,0 +1,6136 @@
+/*
+ *  Generic process-grouping system.
+ *
+ *  Based originally on the cpuset system, extracted by Paul Menage
+ *  Copyright (C) 2006 Google, Inc
+ *
+ *  Notifications support
+ *  Copyright (C) 2009 Nokia Corporation
+ *  Author: Kirill A. Shutemov
+ *
+ *  Copyright notices from the original cpuset code:
+ *  --------------------------------------------------
+ *  Copyright (C) 2003 BULL SA.
+ *  Copyright (C) 2004-2006 Silicon Graphics, Inc.
+ *
+ *  Portions derived from Patrick Mochel's sysfs code.
+ *  sysfs is Copyright (c) 2001-3 Patrick Mochel
+ *
+ *  2003-10-10 Written by Simon Derr.
+ *  2003-10-22 Updates by Stephen Hemminger.
+ *  2004 May-July Rework by Paul Jackson.
+ *  ---------------------------------------------------
+ *
+ *  This file is subject to the terms and conditions of the GNU General Public
+ *  License.  See the file COPYING in the main directory of the Linux
+ *  distribution for more details.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include "cgroup-internal.h"
+
+#include <linux/cred.h>
+#include <linux/errno.h>
+#include <linux/init_task.h>
+#include <linux/kernel.h>
+#include <linux/magic.h>
+#include <linux/mutex.h>
+#include <linux/mount.h>
+#include <linux/pagemap.h>
+#include <linux/proc_fs.h>
+#include <linux/rcupdate.h>
+#include <linux/sched.h>
+#include <linux/sched/task.h>
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+#include <linux/percpu-rwsem.h>
+#include <linux/string.h>
+#include <linux/hashtable.h>
+#include <linux/idr.h>
+#include <linux/kthread.h>
+#include <linux/atomic.h>
+#include <linux/cpuset.h>
+#include <linux/proc_ns.h>
+#include <linux/nsproxy.h>
+#include <linux/file.h>
+#include <linux/sched/cputime.h>
+#include <net/sock.h>
+
+#define CREATE_TRACE_POINTS
+#include <trace/events/cgroup.h>
+
+#define CGROUP_FILE_NAME_MAX		(MAX_CGROUP_TYPE_NAMELEN +	\
+					 MAX_CFTYPE_NAME + 2)
+/* let's not notify more than 100 times per second */
+#define CGROUP_FILE_NOTIFY_MIN_INTV	DIV_ROUND_UP(HZ, 100)
+
+/*
+ * cgroup_mutex is the master lock.  Any modification to cgroup or its
+ * hierarchy must be performed while holding it.
+ *
+ * css_set_lock protects task->cgroups pointer, the list of css_set
+ * objects, and the chain of tasks off each css_set.
+ *
+ * These locks are exported if CONFIG_PROVE_RCU so that accessors in
+ * cgroup.h can use them for lockdep annotations.
+ */
+DEFINE_MUTEX(cgroup_mutex);
+DEFINE_SPINLOCK(css_set_lock);
+
+#ifdef CONFIG_PROVE_RCU
+EXPORT_SYMBOL_GPL(cgroup_mutex);
+EXPORT_SYMBOL_GPL(css_set_lock);
+#endif
+
+DEFINE_SPINLOCK(trace_cgroup_path_lock);
+char trace_cgroup_path[TRACE_CGROUP_PATH_LEN];
+
+/*
+ * Protects cgroup_idr and css_idr so that IDs can be released without
+ * grabbing cgroup_mutex.
+ */
+static DEFINE_SPINLOCK(cgroup_idr_lock);
+
+/*
+ * Protects cgroup_file->kn for !self csses.  It synchronizes notifications
+ * against file removal/re-creation across css hiding.
+ */
+static DEFINE_SPINLOCK(cgroup_file_kn_lock);
+
+struct percpu_rw_semaphore cgroup_threadgroup_rwsem;
+
+#define cgroup_assert_mutex_or_rcu_locked()				\
+	RCU_LOCKDEP_WARN(!rcu_read_lock_held() &&			\
+			   !lockdep_is_held(&cgroup_mutex),		\
+			   "cgroup_mutex or RCU read lock required");
+
+/*
+ * cgroup destruction makes heavy use of work items and there can be a lot
+ * of concurrent destructions.  Use a separate workqueue so that cgroup
+ * destruction work items don't end up filling up max_active of system_wq
+ * which may lead to deadlock.
+ */
+static struct workqueue_struct *cgroup_destroy_wq;
+
+/* generate an array of cgroup subsystem pointers */
+#define SUBSYS(_x) [_x ## _cgrp_id] = &_x ## _cgrp_subsys,
+struct cgroup_subsys *cgroup_subsys[] = {
+#include <linux/cgroup_subsys.h>
+};
+#undef SUBSYS
+
+/* array of cgroup subsystem names */
+#define SUBSYS(_x) [_x ## _cgrp_id] = #_x,
+static const char *cgroup_subsys_name[] = {
+#include <linux/cgroup_subsys.h>
+};
+#undef SUBSYS
+
+/* array of static_keys for cgroup_subsys_enabled() and cgroup_subsys_on_dfl() */
+#define SUBSYS(_x)								\
+	DEFINE_STATIC_KEY_TRUE(_x ## _cgrp_subsys_enabled_key);			\
+	DEFINE_STATIC_KEY_TRUE(_x ## _cgrp_subsys_on_dfl_key);			\
+	EXPORT_SYMBOL_GPL(_x ## _cgrp_subsys_enabled_key);			\
+	EXPORT_SYMBOL_GPL(_x ## _cgrp_subsys_on_dfl_key);
+#include <linux/cgroup_subsys.h>
+#undef SUBSYS
+
+#define SUBSYS(_x) [_x ## _cgrp_id] = &_x ## _cgrp_subsys_enabled_key,
+static struct static_key_true *cgroup_subsys_enabled_key[] = {
+#include <linux/cgroup_subsys.h>
+};
+#undef SUBSYS
+
+#define SUBSYS(_x) [_x ## _cgrp_id] = &_x ## _cgrp_subsys_on_dfl_key,
+static struct static_key_true *cgroup_subsys_on_dfl_key[] = {
+#include <linux/cgroup_subsys.h>
+};
+#undef SUBSYS
+
+static DEFINE_PER_CPU(struct cgroup_rstat_cpu, cgrp_dfl_root_rstat_cpu);
+
+/*
+ * The default hierarchy, reserved for the subsystems that are otherwise
+ * unattached - it never has more than a single cgroup, and all tasks are
+ * part of that cgroup.
+ */
+struct cgroup_root cgrp_dfl_root = { .cgrp.rstat_cpu = &cgrp_dfl_root_rstat_cpu };
+EXPORT_SYMBOL_GPL(cgrp_dfl_root);
+
+/*
+ * The default hierarchy always exists but is hidden until mounted for the
+ * first time.  This is for backward compatibility.
+ */
+static bool cgrp_dfl_visible;
+
+/* some controllers are not supported in the default hierarchy */
+static u16 cgrp_dfl_inhibit_ss_mask;
+
+/* some controllers are implicitly enabled on the default hierarchy */
+static u16 cgrp_dfl_implicit_ss_mask;
+
+/* some controllers can be threaded on the default hierarchy */
+static u16 cgrp_dfl_threaded_ss_mask;
+
+/* The list of hierarchy roots */
+LIST_HEAD(cgroup_roots);
+static int cgroup_root_count;
+
+/* hierarchy ID allocation and mapping, protected by cgroup_mutex */
+static DEFINE_IDR(cgroup_hierarchy_idr);
+
+/*
+ * Assign a monotonically increasing serial number to csses.  It guarantees
+ * cgroups with bigger numbers are newer than those with smaller numbers.
+ * Also, as csses are always appended to the parent's ->children list, it
+ * guarantees that sibling csses are always sorted in the ascending serial
+ * number order on the list.  Protected by cgroup_mutex.
+ */
+static u64 css_serial_nr_next = 1;
+
+/*
+ * These bitmasks identify subsystems with specific features to avoid
+ * having to do iterative checks repeatedly.
+ */
+static u16 have_fork_callback __read_mostly;
+static u16 have_exit_callback __read_mostly;
+static u16 have_release_callback __read_mostly;
+static u16 have_canfork_callback __read_mostly;
+
+/* cgroup namespace for init task */
+struct cgroup_namespace init_cgroup_ns = {
+	.count		= REFCOUNT_INIT(2),
+	.user_ns	= &init_user_ns,
+	.ns.ops		= &cgroupns_operations,
+	.ns.inum	= PROC_CGROUP_INIT_INO,
+	.root_cset	= &init_css_set,
+};
+
+static struct file_system_type cgroup2_fs_type;
+static struct cftype cgroup_base_files[];
+
+static int cgroup_apply_control(struct cgroup *cgrp);
+static void cgroup_finalize_control(struct cgroup *cgrp, int ret);
+static void css_task_iter_skip(struct css_task_iter *it,
+			       struct task_struct *task);
+static int cgroup_destroy_locked(struct cgroup *cgrp);
+static struct cgroup_subsys_state *css_create(struct cgroup *cgrp,
+					      struct cgroup_subsys *ss);
+static void css_release(struct percpu_ref *ref);
+static void kill_css(struct cgroup_subsys_state *css);
+static int cgroup_addrm_files(struct cgroup_subsys_state *css,
+			      struct cgroup *cgrp, struct cftype cfts[],
+			      bool is_add);
+
+/**
+ * cgroup_ssid_enabled - cgroup subsys enabled test by subsys ID
+ * @ssid: subsys ID of interest
+ *
+ * cgroup_subsys_enabled() can only be used with literal subsys names which
+ * is fine for individual subsystems but unsuitable for cgroup core.  This
+ * is slower static_key_enabled() based test indexed by @ssid.
+ */
+bool cgroup_ssid_enabled(int ssid)
+{
+	if (CGROUP_SUBSYS_COUNT == 0)
+		return false;
+
+	return static_key_enabled(cgroup_subsys_enabled_key[ssid]);
+}
+
+/**
+ * cgroup_on_dfl - test whether a cgroup is on the default hierarchy
+ * @cgrp: the cgroup of interest
+ *
+ * The default hierarchy is the v2 interface of cgroup and this function
+ * can be used to test whether a cgroup is on the default hierarchy for
+ * cases where a subsystem should behave differnetly depending on the
+ * interface version.
+ *
+ * The set of behaviors which change on the default hierarchy are still
+ * being determined and the mount option is prefixed with __DEVEL__.
+ *
+ * List of changed behaviors:
+ *
+ * - Mount options "noprefix", "xattr", "clone_children", "release_agent"
+ *   and "name" are disallowed.
+ *
+ * - When mounting an existing superblock, mount options should match.
+ *
+ * - Remount is disallowed.
+ *
+ * - rename(2) is disallowed.
+ *
+ * - "tasks" is removed.  Everything should be at process granularity.  Use
+ *   "cgroup.procs" instead.
+ *
+ * - "cgroup.procs" is not sorted.  pids will be unique unless they got
+ *   recycled inbetween reads.
+ *
+ * - "release_agent" and "notify_on_release" are removed.  Replacement
+ *   notification mechanism will be implemented.
+ *
+ * - "cgroup.clone_children" is removed.
+ *
+ * - "cgroup.subtree_populated" is available.  Its value is 0 if the cgroup
+ *   and its descendants contain no task; otherwise, 1.  The file also
+ *   generates kernfs notification which can be monitored through poll and
+ *   [di]notify when the value of the file changes.
+ *
+ * - cpuset: tasks will be kept in empty cpusets when hotplug happens and
+ *   take masks of ancestors with non-empty cpus/mems, instead of being
+ *   moved to an ancestor.
+ *
+ * - cpuset: a task can be moved into an empty cpuset, and again it takes
+ *   masks of ancestors.
+ *
+ * - memcg: use_hierarchy is on by default and the cgroup file for the flag
+ *   is not created.
+ *
+ * - blkcg: blk-throttle becomes properly hierarchical.
+ *
+ * - debug: disallowed on the default hierarchy.
+ */
+bool cgroup_on_dfl(const struct cgroup *cgrp)
+{
+	return cgrp->root == &cgrp_dfl_root;
+}
+
+/* IDR wrappers which synchronize using cgroup_idr_lock */
+static int cgroup_idr_alloc(struct idr *idr, void *ptr, int start, int end,
+			    gfp_t gfp_mask)
+{
+	int ret;
+
+	idr_preload(gfp_mask);
+	spin_lock_bh(&cgroup_idr_lock);
+	ret = idr_alloc(idr, ptr, start, end, gfp_mask & ~__GFP_DIRECT_RECLAIM);
+	spin_unlock_bh(&cgroup_idr_lock);
+	idr_preload_end();
+	return ret;
+}
+
+static void *cgroup_idr_replace(struct idr *idr, void *ptr, int id)
+{
+	void *ret;
+
+	spin_lock_bh(&cgroup_idr_lock);
+	ret = idr_replace(idr, ptr, id);
+	spin_unlock_bh(&cgroup_idr_lock);
+	return ret;
+}
+
+static void cgroup_idr_remove(struct idr *idr, int id)
+{
+	spin_lock_bh(&cgroup_idr_lock);
+	idr_remove(idr, id);
+	spin_unlock_bh(&cgroup_idr_lock);
+}
+
+static bool cgroup_has_tasks(struct cgroup *cgrp)
+{
+	return cgrp->nr_populated_csets;
+}
+
+bool cgroup_is_threaded(struct cgroup *cgrp)
+{
+	return cgrp->dom_cgrp != cgrp;
+}
+
+/* can @cgrp host both domain and threaded children? */
+static bool cgroup_is_mixable(struct cgroup *cgrp)
+{
+	/*
+	 * Root isn't under domain level resource control exempting it from
+	 * the no-internal-process constraint, so it can serve as a thread
+	 * root and a parent of resource domains at the same time.
+	 */
+	return !cgroup_parent(cgrp);
+}
+
+/* can @cgrp become a thread root? should always be true for a thread root */
+static bool cgroup_can_be_thread_root(struct cgroup *cgrp)
+{
+	/* mixables don't care */
+	if (cgroup_is_mixable(cgrp))
+		return true;
+
+	/* domain roots can't be nested under threaded */
+	if (cgroup_is_threaded(cgrp))
+		return false;
+
+	/* can only have either domain or threaded children */
+	if (cgrp->nr_populated_domain_children)
+		return false;
+
+	/* and no domain controllers can be enabled */
+	if (cgrp->subtree_control & ~cgrp_dfl_threaded_ss_mask)
+		return false;
+
+	return true;
+}
+
+/* is @cgrp root of a threaded subtree? */
+bool cgroup_is_thread_root(struct cgroup *cgrp)
+{
+	/* thread root should be a domain */
+	if (cgroup_is_threaded(cgrp))
+		return false;
+
+	/* a domain w/ threaded children is a thread root */
+	if (cgrp->nr_threaded_children)
+		return true;
+
+	/*
+	 * A domain which has tasks and explicit threaded controllers
+	 * enabled is a thread root.
+	 */
+	if (cgroup_has_tasks(cgrp) &&
+	    (cgrp->subtree_control & cgrp_dfl_threaded_ss_mask))
+		return true;
+
+	return false;
+}
+
+/* a domain which isn't connected to the root w/o brekage can't be used */
+static bool cgroup_is_valid_domain(struct cgroup *cgrp)
+{
+	/* the cgroup itself can be a thread root */
+	if (cgroup_is_threaded(cgrp))
+		return false;
+
+	/* but the ancestors can't be unless mixable */
+	while ((cgrp = cgroup_parent(cgrp))) {
+		if (!cgroup_is_mixable(cgrp) && cgroup_is_thread_root(cgrp))
+			return false;
+		if (cgroup_is_threaded(cgrp))
+			return false;
+	}
+
+	return true;
+}
+
+/* subsystems visibly enabled on a cgroup */
+static u16 cgroup_control(struct cgroup *cgrp)
+{
+	struct cgroup *parent = cgroup_parent(cgrp);
+	u16 root_ss_mask = cgrp->root->subsys_mask;
+
+	if (parent) {
+		u16 ss_mask = parent->subtree_control;
+
+		/* threaded cgroups can only have threaded controllers */
+		if (cgroup_is_threaded(cgrp))
+			ss_mask &= cgrp_dfl_threaded_ss_mask;
+		return ss_mask;
+	}
+
+	if (cgroup_on_dfl(cgrp))
+		root_ss_mask &= ~(cgrp_dfl_inhibit_ss_mask |
+				  cgrp_dfl_implicit_ss_mask);
+	return root_ss_mask;
+}
+
+/* subsystems enabled on a cgroup */
+static u16 cgroup_ss_mask(struct cgroup *cgrp)
+{
+	struct cgroup *parent = cgroup_parent(cgrp);
+
+	if (parent) {
+		u16 ss_mask = parent->subtree_ss_mask;
+
+		/* threaded cgroups can only have threaded controllers */
+		if (cgroup_is_threaded(cgrp))
+			ss_mask &= cgrp_dfl_threaded_ss_mask;
+		return ss_mask;
+	}
+
+	return cgrp->root->subsys_mask;
+}
+
+/**
+ * cgroup_css - obtain a cgroup's css for the specified subsystem
+ * @cgrp: the cgroup of interest
+ * @ss: the subsystem of interest (%NULL returns @cgrp->self)
+ *
+ * Return @cgrp's css (cgroup_subsys_state) associated with @ss.  This
+ * function must be called either under cgroup_mutex or rcu_read_lock() and
+ * the caller is responsible for pinning the returned css if it wants to
+ * keep accessing it outside the said locks.  This function may return
+ * %NULL if @cgrp doesn't have @subsys_id enabled.
+ */
+static struct cgroup_subsys_state *cgroup_css(struct cgroup *cgrp,
+					      struct cgroup_subsys *ss)
+{
+	if (ss)
+		return rcu_dereference_check(cgrp->subsys[ss->id],
+					lockdep_is_held(&cgroup_mutex));
+	else
+		return &cgrp->self;
+}
+
+/**
+ * cgroup_tryget_css - try to get a cgroup's css for the specified subsystem
+ * @cgrp: the cgroup of interest
+ * @ss: the subsystem of interest
+ *
+ * Find and get @cgrp's css assocaited with @ss.  If the css doesn't exist
+ * or is offline, %NULL is returned.
+ */
+static struct cgroup_subsys_state *cgroup_tryget_css(struct cgroup *cgrp,
+						     struct cgroup_subsys *ss)
+{
+	struct cgroup_subsys_state *css;
+
+	rcu_read_lock();
+	css = cgroup_css(cgrp, ss);
+	if (!css || !css_tryget_online(css))
+		css = NULL;
+	rcu_read_unlock();
+
+	return css;
+}
+
+/**
+ * cgroup_e_css - obtain a cgroup's effective css for the specified subsystem
+ * @cgrp: the cgroup of interest
+ * @ss: the subsystem of interest (%NULL returns @cgrp->self)
+ *
+ * Similar to cgroup_css() but returns the effective css, which is defined
+ * as the matching css of the nearest ancestor including self which has @ss
+ * enabled.  If @ss is associated with the hierarchy @cgrp is on, this
+ * function is guaranteed to return non-NULL css.
+ */
+static struct cgroup_subsys_state *cgroup_e_css(struct cgroup *cgrp,
+						struct cgroup_subsys *ss)
+{
+	lockdep_assert_held(&cgroup_mutex);
+
+	if (!ss)
+		return &cgrp->self;
+
+	/*
+	 * This function is used while updating css associations and thus
+	 * can't test the csses directly.  Test ss_mask.
+	 */
+	while (!(cgroup_ss_mask(cgrp) & (1 << ss->id))) {
+		cgrp = cgroup_parent(cgrp);
+		if (!cgrp)
+			return NULL;
+	}
+
+	return cgroup_css(cgrp, ss);
+}
+
+/**
+ * cgroup_get_e_css - get a cgroup's effective css for the specified subsystem
+ * @cgrp: the cgroup of interest
+ * @ss: the subsystem of interest
+ *
+ * Find and get the effective css of @cgrp for @ss.  The effective css is
+ * defined as the matching css of the nearest ancestor including self which
+ * has @ss enabled.  If @ss is not mounted on the hierarchy @cgrp is on,
+ * the root css is returned, so this function always returns a valid css.
+ * The returned css must be put using css_put().
+ */
+struct cgroup_subsys_state *cgroup_get_e_css(struct cgroup *cgrp,
+					     struct cgroup_subsys *ss)
+{
+	struct cgroup_subsys_state *css;
+
+	rcu_read_lock();
+
+	do {
+		css = cgroup_css(cgrp, ss);
+
+		if (css && css_tryget_online(css))
+			goto out_unlock;
+		cgrp = cgroup_parent(cgrp);
+	} while (cgrp);
+
+	css = init_css_set.subsys[ss->id];
+	css_get(css);
+out_unlock:
+	rcu_read_unlock();
+	return css;
+}
+
+static void cgroup_get_live(struct cgroup *cgrp)
+{
+	WARN_ON_ONCE(cgroup_is_dead(cgrp));
+	css_get(&cgrp->self);
+}
+
+struct cgroup_subsys_state *of_css(struct kernfs_open_file *of)
+{
+	struct cgroup *cgrp = of->kn->parent->priv;
+	struct cftype *cft = of_cft(of);
+
+	/*
+	 * This is open and unprotected implementation of cgroup_css().
+	 * seq_css() is only called from a kernfs file operation which has
+	 * an active reference on the file.  Because all the subsystem
+	 * files are drained before a css is disassociated with a cgroup,
+	 * the matching css from the cgroup's subsys table is guaranteed to
+	 * be and stay valid until the enclosing operation is complete.
+	 */
+	if (cft->ss)
+		return rcu_dereference_raw(cgrp->subsys[cft->ss->id]);
+	else
+		return &cgrp->self;
+}
+EXPORT_SYMBOL_GPL(of_css);
+
+/**
+ * for_each_css - iterate all css's of a cgroup
+ * @css: the iteration cursor
+ * @ssid: the index of the subsystem, CGROUP_SUBSYS_COUNT after reaching the end
+ * @cgrp: the target cgroup to iterate css's of
+ *
+ * Should be called under cgroup_[tree_]mutex.
+ */
+#define for_each_css(css, ssid, cgrp)					\
+	for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT; (ssid)++)	\
+		if (!((css) = rcu_dereference_check(			\
+				(cgrp)->subsys[(ssid)],			\
+				lockdep_is_held(&cgroup_mutex)))) { }	\
+		else
+
+/**
+ * for_each_e_css - iterate all effective css's of a cgroup
+ * @css: the iteration cursor
+ * @ssid: the index of the subsystem, CGROUP_SUBSYS_COUNT after reaching the end
+ * @cgrp: the target cgroup to iterate css's of
+ *
+ * Should be called under cgroup_[tree_]mutex.
+ */
+#define for_each_e_css(css, ssid, cgrp)					\
+	for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT; (ssid)++)	\
+		if (!((css) = cgroup_e_css(cgrp, cgroup_subsys[(ssid)]))) \
+			;						\
+		else
+
+/**
+ * do_each_subsys_mask - filter for_each_subsys with a bitmask
+ * @ss: the iteration cursor
+ * @ssid: the index of @ss, CGROUP_SUBSYS_COUNT after reaching the end
+ * @ss_mask: the bitmask
+ *
+ * The block will only run for cases where the ssid-th bit (1 << ssid) of
+ * @ss_mask is set.
+ */
+#define do_each_subsys_mask(ss, ssid, ss_mask) do {			\
+	unsigned long __ss_mask = (ss_mask);				\
+	if (!CGROUP_SUBSYS_COUNT) { /* to avoid spurious gcc warning */	\
+		(ssid) = 0;						\
+		break;							\
+	}								\
+	for_each_set_bit(ssid, &__ss_mask, CGROUP_SUBSYS_COUNT) {	\
+		(ss) = cgroup_subsys[ssid];				\
+		{
+
+#define while_each_subsys_mask()					\
+		}							\
+	}								\
+} while (false)
+
+/* iterate over child cgrps, lock should be held throughout iteration */
+#define cgroup_for_each_live_child(child, cgrp)				\
+	list_for_each_entry((child), &(cgrp)->self.children, self.sibling) \
+		if (({ lockdep_assert_held(&cgroup_mutex);		\
+		       cgroup_is_dead(child); }))			\
+			;						\
+		else
+
+/* walk live descendants in preorder */
+#define cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp)		\
+	css_for_each_descendant_pre((d_css), cgroup_css((cgrp), NULL))	\
+		if (({ lockdep_assert_held(&cgroup_mutex);		\
+		       (dsct) = (d_css)->cgroup;			\
+		       cgroup_is_dead(dsct); }))			\
+			;						\
+		else
+
+/* walk live descendants in postorder */
+#define cgroup_for_each_live_descendant_post(dsct, d_css, cgrp)		\
+	css_for_each_descendant_post((d_css), cgroup_css((cgrp), NULL))	\
+		if (({ lockdep_assert_held(&cgroup_mutex);		\
+		       (dsct) = (d_css)->cgroup;			\
+		       cgroup_is_dead(dsct); }))			\
+			;						\
+		else
+
+/*
+ * The default css_set - used by init and its children prior to any
+ * hierarchies being mounted. It contains a pointer to the root state
+ * for each subsystem. Also used to anchor the list of css_sets. Not
+ * reference-counted, to improve performance when child cgroups
+ * haven't been created.
+ */
+struct css_set init_css_set = {
+	.refcount		= REFCOUNT_INIT(1),
+	.dom_cset		= &init_css_set,
+	.tasks			= LIST_HEAD_INIT(init_css_set.tasks),
+	.mg_tasks		= LIST_HEAD_INIT(init_css_set.mg_tasks),
+	.dying_tasks		= LIST_HEAD_INIT(init_css_set.dying_tasks),
+	.task_iters		= LIST_HEAD_INIT(init_css_set.task_iters),
+	.threaded_csets		= LIST_HEAD_INIT(init_css_set.threaded_csets),
+	.cgrp_links		= LIST_HEAD_INIT(init_css_set.cgrp_links),
+	.mg_preload_node	= LIST_HEAD_INIT(init_css_set.mg_preload_node),
+	.mg_node		= LIST_HEAD_INIT(init_css_set.mg_node),
+
+	/*
+	 * The following field is re-initialized when this cset gets linked
+	 * in cgroup_init().  However, let's initialize the field
+	 * statically too so that the default cgroup can be accessed safely
+	 * early during boot.
+	 */
+	.dfl_cgrp		= &cgrp_dfl_root.cgrp,
+};
+
+static int css_set_count	= 1;	/* 1 for init_css_set */
+
+static bool css_set_threaded(struct css_set *cset)
+{
+	return cset->dom_cset != cset;
+}
+
+/**
+ * css_set_populated - does a css_set contain any tasks?
+ * @cset: target css_set
+ *
+ * css_set_populated() should be the same as !!cset->nr_tasks at steady
+ * state. However, css_set_populated() can be called while a task is being
+ * added to or removed from the linked list before the nr_tasks is
+ * properly updated. Hence, we can't just look at ->nr_tasks here.
+ */
+static bool css_set_populated(struct css_set *cset)
+{
+	lockdep_assert_held(&css_set_lock);
+
+	return !list_empty(&cset->tasks) || !list_empty(&cset->mg_tasks);
+}
+
+/**
+ * cgroup_update_populated - update the populated count of a cgroup
+ * @cgrp: the target cgroup
+ * @populated: inc or dec populated count
+ *
+ * One of the css_sets associated with @cgrp is either getting its first
+ * task or losing the last.  Update @cgrp->nr_populated_* accordingly.  The
+ * count is propagated towards root so that a given cgroup's
+ * nr_populated_children is zero iff none of its descendants contain any
+ * tasks.
+ *
+ * @cgrp's interface file "cgroup.populated" is zero if both
+ * @cgrp->nr_populated_csets and @cgrp->nr_populated_children are zero and
+ * 1 otherwise.  When the sum changes from or to zero, userland is notified
+ * that the content of the interface file has changed.  This can be used to
+ * detect when @cgrp and its descendants become populated or empty.
+ */
+static void cgroup_update_populated(struct cgroup *cgrp, bool populated)
+{
+	struct cgroup *child = NULL;
+	int adj = populated ? 1 : -1;
+
+	lockdep_assert_held(&css_set_lock);
+
+	do {
+		bool was_populated = cgroup_is_populated(cgrp);
+
+		if (!child) {
+			cgrp->nr_populated_csets += adj;
+		} else {
+			if (cgroup_is_threaded(child))
+				cgrp->nr_populated_threaded_children += adj;
+			else
+				cgrp->nr_populated_domain_children += adj;
+		}
+
+		if (was_populated == cgroup_is_populated(cgrp))
+			break;
+
+		cgroup1_check_for_release(cgrp);
+		cgroup_file_notify(&cgrp->events_file);
+
+		child = cgrp;
+		cgrp = cgroup_parent(cgrp);
+	} while (cgrp);
+}
+
+/**
+ * css_set_update_populated - update populated state of a css_set
+ * @cset: target css_set
+ * @populated: whether @cset is populated or depopulated
+ *
+ * @cset is either getting the first task or losing the last.  Update the
+ * populated counters of all associated cgroups accordingly.
+ */
+static void css_set_update_populated(struct css_set *cset, bool populated)
+{
+	struct cgrp_cset_link *link;
+
+	lockdep_assert_held(&css_set_lock);
+
+	list_for_each_entry(link, &cset->cgrp_links, cgrp_link)
+		cgroup_update_populated(link->cgrp, populated);
+}
+
+/*
+ * @task is leaving, advance task iterators which are pointing to it so
+ * that they can resume at the next position.  Advancing an iterator might
+ * remove it from the list, use safe walk.  See css_task_iter_skip() for
+ * details.
+ */
+static void css_set_skip_task_iters(struct css_set *cset,
+				    struct task_struct *task)
+{
+	struct css_task_iter *it, *pos;
+
+	list_for_each_entry_safe(it, pos, &cset->task_iters, iters_node)
+		css_task_iter_skip(it, task);
+}
+
+/**
+ * css_set_move_task - move a task from one css_set to another
+ * @task: task being moved
+ * @from_cset: css_set @task currently belongs to (may be NULL)
+ * @to_cset: new css_set @task is being moved to (may be NULL)
+ * @use_mg_tasks: move to @to_cset->mg_tasks instead of ->tasks
+ *
+ * Move @task from @from_cset to @to_cset.  If @task didn't belong to any
+ * css_set, @from_cset can be NULL.  If @task is being disassociated
+ * instead of moved, @to_cset can be NULL.
+ *
+ * This function automatically handles populated counter updates and
+ * css_task_iter adjustments but the caller is responsible for managing
+ * @from_cset and @to_cset's reference counts.
+ */
+static void css_set_move_task(struct task_struct *task,
+			      struct css_set *from_cset, struct css_set *to_cset,
+			      bool use_mg_tasks)
+{
+	lockdep_assert_held(&css_set_lock);
+
+	if (to_cset && !css_set_populated(to_cset))
+		css_set_update_populated(to_cset, true);
+
+	if (from_cset) {
+		WARN_ON_ONCE(list_empty(&task->cg_list));
+
+		css_set_skip_task_iters(from_cset, task);
+		list_del_init(&task->cg_list);
+		if (!css_set_populated(from_cset))
+			css_set_update_populated(from_cset, false);
+	} else {
+		WARN_ON_ONCE(!list_empty(&task->cg_list));
+	}
+
+	if (to_cset) {
+		/*
+		 * We are synchronized through cgroup_threadgroup_rwsem
+		 * against PF_EXITING setting such that we can't race
+		 * against cgroup_exit() changing the css_set to
+		 * init_css_set and dropping the old one.
+		 */
+		WARN_ON_ONCE(task->flags & PF_EXITING);
+
+		rcu_assign_pointer(task->cgroups, to_cset);
+		list_add_tail(&task->cg_list, use_mg_tasks ? &to_cset->mg_tasks :
+							     &to_cset->tasks);
+	}
+}
+
+/*
+ * hash table for cgroup groups. This improves the performance to find
+ * an existing css_set. This hash doesn't (currently) take into
+ * account cgroups in empty hierarchies.
+ */
+#define CSS_SET_HASH_BITS	7
+static DEFINE_HASHTABLE(css_set_table, CSS_SET_HASH_BITS);
+
+static unsigned long css_set_hash(struct cgroup_subsys_state *css[])
+{
+	unsigned long key = 0UL;
+	struct cgroup_subsys *ss;
+	int i;
+
+	for_each_subsys(ss, i)
+		key += (unsigned long)css[i];
+	key = (key >> 16) ^ key;
+
+	return key;
+}
+
+void put_css_set_locked(struct css_set *cset)
+{
+	struct cgrp_cset_link *link, *tmp_link;
+	struct cgroup_subsys *ss;
+	int ssid;
+
+	lockdep_assert_held(&css_set_lock);
+
+	if (!refcount_dec_and_test(&cset->refcount))
+		return;
+
+	WARN_ON_ONCE(!list_empty(&cset->threaded_csets));
+
+	/* This css_set is dead. unlink it and release cgroup and css refs */
+	for_each_subsys(ss, ssid) {
+		list_del(&cset->e_cset_node[ssid]);
+		css_put(cset->subsys[ssid]);
+	}
+	hash_del(&cset->hlist);
+	css_set_count--;
+
+	list_for_each_entry_safe(link, tmp_link, &cset->cgrp_links, cgrp_link) {
+		list_del(&link->cset_link);
+		list_del(&link->cgrp_link);
+		if (cgroup_parent(link->cgrp))
+			cgroup_put(link->cgrp);
+		kfree(link);
+	}
+
+	if (css_set_threaded(cset)) {
+		list_del(&cset->threaded_csets_node);
+		put_css_set_locked(cset->dom_cset);
+	}
+
+	kfree_rcu(cset, rcu_head);
+}
+
+/**
+ * compare_css_sets - helper function for find_existing_css_set().
+ * @cset: candidate css_set being tested
+ * @old_cset: existing css_set for a task
+ * @new_cgrp: cgroup that's being entered by the task
+ * @template: desired set of css pointers in css_set (pre-calculated)
+ *
+ * Returns true if "cset" matches "old_cset" except for the hierarchy
+ * which "new_cgrp" belongs to, for which it should match "new_cgrp".
+ */
+static bool compare_css_sets(struct css_set *cset,
+			     struct css_set *old_cset,
+			     struct cgroup *new_cgrp,
+			     struct cgroup_subsys_state *template[])
+{
+	struct cgroup *new_dfl_cgrp;
+	struct list_head *l1, *l2;
+
+	/*
+	 * On the default hierarchy, there can be csets which are
+	 * associated with the same set of cgroups but different csses.
+	 * Let's first ensure that csses match.
+	 */
+	if (memcmp(template, cset->subsys, sizeof(cset->subsys)))
+		return false;
+
+
+	/* @cset's domain should match the default cgroup's */
+	if (cgroup_on_dfl(new_cgrp))
+		new_dfl_cgrp = new_cgrp;
+	else
+		new_dfl_cgrp = old_cset->dfl_cgrp;
+
+	if (new_dfl_cgrp->dom_cgrp != cset->dom_cset->dfl_cgrp)
+		return false;
+
+	/*
+	 * Compare cgroup pointers in order to distinguish between
+	 * different cgroups in hierarchies.  As different cgroups may
+	 * share the same effective css, this comparison is always
+	 * necessary.
+	 */
+	l1 = &cset->cgrp_links;
+	l2 = &old_cset->cgrp_links;
+	while (1) {
+		struct cgrp_cset_link *link1, *link2;
+		struct cgroup *cgrp1, *cgrp2;
+
+		l1 = l1->next;
+		l2 = l2->next;
+		/* See if we reached the end - both lists are equal length. */
+		if (l1 == &cset->cgrp_links) {
+			BUG_ON(l2 != &old_cset->cgrp_links);
+			break;
+		} else {
+			BUG_ON(l2 == &old_cset->cgrp_links);
+		}
+		/* Locate the cgroups associated with these links. */
+		link1 = list_entry(l1, struct cgrp_cset_link, cgrp_link);
+		link2 = list_entry(l2, struct cgrp_cset_link, cgrp_link);
+		cgrp1 = link1->cgrp;
+		cgrp2 = link2->cgrp;
+		/* Hierarchies should be linked in the same order. */
+		BUG_ON(cgrp1->root != cgrp2->root);
+
+		/*
+		 * If this hierarchy is the hierarchy of the cgroup
+		 * that's changing, then we need to check that this
+		 * css_set points to the new cgroup; if it's any other
+		 * hierarchy, then this css_set should point to the
+		 * same cgroup as the old css_set.
+		 */
+		if (cgrp1->root == new_cgrp->root) {
+			if (cgrp1 != new_cgrp)
+				return false;
+		} else {
+			if (cgrp1 != cgrp2)
+				return false;
+		}
+	}
+	return true;
+}
+
+/**
+ * find_existing_css_set - init css array and find the matching css_set
+ * @old_cset: the css_set that we're using before the cgroup transition
+ * @cgrp: the cgroup that we're moving into
+ * @template: out param for the new set of csses, should be clear on entry
+ */
+static struct css_set *find_existing_css_set(struct css_set *old_cset,
+					struct cgroup *cgrp,
+					struct cgroup_subsys_state *template[])
+{
+	struct cgroup_root *root = cgrp->root;
+	struct cgroup_subsys *ss;
+	struct css_set *cset;
+	unsigned long key;
+	int i;
+
+	/*
+	 * Build the set of subsystem state objects that we want to see in the
+	 * new css_set. while subsystems can change globally, the entries here
+	 * won't change, so no need for locking.
+	 */
+	for_each_subsys(ss, i) {
+		if (root->subsys_mask & (1UL << i)) {
+			/*
+			 * @ss is in this hierarchy, so we want the
+			 * effective css from @cgrp.
+			 */
+			template[i] = cgroup_e_css(cgrp, ss);
+		} else {
+			/*
+			 * @ss is not in this hierarchy, so we don't want
+			 * to change the css.
+			 */
+			template[i] = old_cset->subsys[i];
+		}
+	}
+
+	key = css_set_hash(template);
+	hash_for_each_possible(css_set_table, cset, hlist, key) {
+		if (!compare_css_sets(cset, old_cset, cgrp, template))
+			continue;
+
+		/* This css_set matches what we need */
+		return cset;
+	}
+
+	/* No existing cgroup group matched */
+	return NULL;
+}
+
+static void free_cgrp_cset_links(struct list_head *links_to_free)
+{
+	struct cgrp_cset_link *link, *tmp_link;
+
+	list_for_each_entry_safe(link, tmp_link, links_to_free, cset_link) {
+		list_del(&link->cset_link);
+		kfree(link);
+	}
+}
+
+/**
+ * allocate_cgrp_cset_links - allocate cgrp_cset_links
+ * @count: the number of links to allocate
+ * @tmp_links: list_head the allocated links are put on
+ *
+ * Allocate @count cgrp_cset_link structures and chain them on @tmp_links
+ * through ->cset_link.  Returns 0 on success or -errno.
+ */
+static int allocate_cgrp_cset_links(int count, struct list_head *tmp_links)
+{
+	struct cgrp_cset_link *link;
+	int i;
+
+	INIT_LIST_HEAD(tmp_links);
+
+	for (i = 0; i < count; i++) {
+		link = kzalloc(sizeof(*link), GFP_KERNEL);
+		if (!link) {
+			free_cgrp_cset_links(tmp_links);
+			return -ENOMEM;
+		}
+		list_add(&link->cset_link, tmp_links);
+	}
+	return 0;
+}
+
+/**
+ * link_css_set - a helper function to link a css_set to a cgroup
+ * @tmp_links: cgrp_cset_link objects allocated by allocate_cgrp_cset_links()
+ * @cset: the css_set to be linked
+ * @cgrp: the destination cgroup
+ */
+static void link_css_set(struct list_head *tmp_links, struct css_set *cset,
+			 struct cgroup *cgrp)
+{
+	struct cgrp_cset_link *link;
+
+	BUG_ON(list_empty(tmp_links));
+
+	if (cgroup_on_dfl(cgrp))
+		cset->dfl_cgrp = cgrp;
+
+	link = list_first_entry(tmp_links, struct cgrp_cset_link, cset_link);
+	link->cset = cset;
+	link->cgrp = cgrp;
+
+	/*
+	 * Always add links to the tail of the lists so that the lists are
+	 * in choronological order.
+	 */
+	list_move_tail(&link->cset_link, &cgrp->cset_links);
+	list_add_tail(&link->cgrp_link, &cset->cgrp_links);
+
+	if (cgroup_parent(cgrp))
+		cgroup_get_live(cgrp);
+}
+
+/**
+ * find_css_set - return a new css_set with one cgroup updated
+ * @old_cset: the baseline css_set
+ * @cgrp: the cgroup to be updated
+ *
+ * Return a new css_set that's equivalent to @old_cset, but with @cgrp
+ * substituted into the appropriate hierarchy.
+ */
+static struct css_set *find_css_set(struct css_set *old_cset,
+				    struct cgroup *cgrp)
+{
+	struct cgroup_subsys_state *template[CGROUP_SUBSYS_COUNT] = { };
+	struct css_set *cset;
+	struct list_head tmp_links;
+	struct cgrp_cset_link *link;
+	struct cgroup_subsys *ss;
+	unsigned long key;
+	int ssid;
+
+	lockdep_assert_held(&cgroup_mutex);
+
+	/* First see if we already have a cgroup group that matches
+	 * the desired set */
+	spin_lock_irq(&css_set_lock);
+	cset = find_existing_css_set(old_cset, cgrp, template);
+	if (cset)
+		get_css_set(cset);
+	spin_unlock_irq(&css_set_lock);
+
+	if (cset)
+		return cset;
+
+	cset = kzalloc(sizeof(*cset), GFP_KERNEL);
+	if (!cset)
+		return NULL;
+
+	/* Allocate all the cgrp_cset_link objects that we'll need */
+	if (allocate_cgrp_cset_links(cgroup_root_count, &tmp_links) < 0) {
+		kfree(cset);
+		return NULL;
+	}
+
+	refcount_set(&cset->refcount, 1);
+	cset->dom_cset = cset;
+	INIT_LIST_HEAD(&cset->tasks);
+	INIT_LIST_HEAD(&cset->mg_tasks);
+	INIT_LIST_HEAD(&cset->dying_tasks);
+	INIT_LIST_HEAD(&cset->task_iters);
+	INIT_LIST_HEAD(&cset->threaded_csets);
+	INIT_HLIST_NODE(&cset->hlist);
+	INIT_LIST_HEAD(&cset->cgrp_links);
+	INIT_LIST_HEAD(&cset->mg_preload_node);
+	INIT_LIST_HEAD(&cset->mg_node);
+
+	/* Copy the set of subsystem state objects generated in
+	 * find_existing_css_set() */
+	memcpy(cset->subsys, template, sizeof(cset->subsys));
+
+	spin_lock_irq(&css_set_lock);
+	/* Add reference counts and links from the new css_set. */
+	list_for_each_entry(link, &old_cset->cgrp_links, cgrp_link) {
+		struct cgroup *c = link->cgrp;
+
+		if (c->root == cgrp->root)
+			c = cgrp;
+		link_css_set(&tmp_links, cset, c);
+	}
+
+	BUG_ON(!list_empty(&tmp_links));
+
+	css_set_count++;
+
+	/* Add @cset to the hash table */
+	key = css_set_hash(cset->subsys);
+	hash_add(css_set_table, &cset->hlist, key);
+
+	for_each_subsys(ss, ssid) {
+		struct cgroup_subsys_state *css = cset->subsys[ssid];
+
+		list_add_tail(&cset->e_cset_node[ssid],
+			      &css->cgroup->e_csets[ssid]);
+		css_get(css);
+	}
+
+	spin_unlock_irq(&css_set_lock);
+
+	/*
+	 * If @cset should be threaded, look up the matching dom_cset and
+	 * link them up.  We first fully initialize @cset then look for the
+	 * dom_cset.  It's simpler this way and safe as @cset is guaranteed
+	 * to stay empty until we return.
+	 */
+	if (cgroup_is_threaded(cset->dfl_cgrp)) {
+		struct css_set *dcset;
+
+		dcset = find_css_set(cset, cset->dfl_cgrp->dom_cgrp);
+		if (!dcset) {
+			put_css_set(cset);
+			return NULL;
+		}
+
+		spin_lock_irq(&css_set_lock);
+		cset->dom_cset = dcset;
+		list_add_tail(&cset->threaded_csets_node,
+			      &dcset->threaded_csets);
+		spin_unlock_irq(&css_set_lock);
+	}
+
+	return cset;
+}
+
+struct cgroup_root *cgroup_root_from_kf(struct kernfs_root *kf_root)
+{
+	struct cgroup *root_cgrp = kf_root->kn->priv;
+
+	return root_cgrp->root;
+}
+
+static int cgroup_init_root_id(struct cgroup_root *root)
+{
+	int id;
+
+	lockdep_assert_held(&cgroup_mutex);
+
+	id = idr_alloc_cyclic(&cgroup_hierarchy_idr, root, 0, 0, GFP_KERNEL);
+	if (id < 0)
+		return id;
+
+	root->hierarchy_id = id;
+	return 0;
+}
+
+static void cgroup_exit_root_id(struct cgroup_root *root)
+{
+	lockdep_assert_held(&cgroup_mutex);
+
+	idr_remove(&cgroup_hierarchy_idr, root->hierarchy_id);
+}
+
+void cgroup_free_root(struct cgroup_root *root)
+{
+	if (root) {
+		idr_destroy(&root->cgroup_idr);
+		kfree(root);
+	}
+}
+
+static void cgroup_destroy_root(struct cgroup_root *root)
+{
+	struct cgroup *cgrp = &root->cgrp;
+	struct cgrp_cset_link *link, *tmp_link;
+
+	trace_cgroup_destroy_root(root);
+
+	cgroup_lock_and_drain_offline(&cgrp_dfl_root.cgrp);
+
+	BUG_ON(atomic_read(&root->nr_cgrps));
+	BUG_ON(!list_empty(&cgrp->self.children));
+
+	/* Rebind all subsystems back to the default hierarchy */
+	WARN_ON(rebind_subsystems(&cgrp_dfl_root, root->subsys_mask));
+
+	/*
+	 * Release all the links from cset_links to this hierarchy's
+	 * root cgroup
+	 */
+	spin_lock_irq(&css_set_lock);
+
+	list_for_each_entry_safe(link, tmp_link, &cgrp->cset_links, cset_link) {
+		list_del(&link->cset_link);
+		list_del(&link->cgrp_link);
+		kfree(link);
+	}
+
+	spin_unlock_irq(&css_set_lock);
+
+	if (!list_empty(&root->root_list)) {
+		list_del(&root->root_list);
+		cgroup_root_count--;
+	}
+
+	cgroup_exit_root_id(root);
+
+	mutex_unlock(&cgroup_mutex);
+
+	kernfs_destroy_root(root->kf_root);
+	cgroup_free_root(root);
+}
+
+/*
+ * look up cgroup associated with current task's cgroup namespace on the
+ * specified hierarchy
+ */
+static struct cgroup *
+current_cgns_cgroup_from_root(struct cgroup_root *root)
+{
+	struct cgroup *res = NULL;
+	struct css_set *cset;
+
+	lockdep_assert_held(&css_set_lock);
+
+	rcu_read_lock();
+
+	cset = current->nsproxy->cgroup_ns->root_cset;
+	if (cset == &init_css_set) {
+		res = &root->cgrp;
+	} else {
+		struct cgrp_cset_link *link;
+
+		list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
+			struct cgroup *c = link->cgrp;
+
+			if (c->root == root) {
+				res = c;
+				break;
+			}
+		}
+	}
+	rcu_read_unlock();
+
+	BUG_ON(!res);
+	return res;
+}
+
+/* look up cgroup associated with given css_set on the specified hierarchy */
+static struct cgroup *cset_cgroup_from_root(struct css_set *cset,
+					    struct cgroup_root *root)
+{
+	struct cgroup *res = NULL;
+
+	lockdep_assert_held(&cgroup_mutex);
+	lockdep_assert_held(&css_set_lock);
+
+	if (cset == &init_css_set) {
+		res = &root->cgrp;
+	} else if (root == &cgrp_dfl_root) {
+		res = cset->dfl_cgrp;
+	} else {
+		struct cgrp_cset_link *link;
+
+		list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
+			struct cgroup *c = link->cgrp;
+
+			if (c->root == root) {
+				res = c;
+				break;
+			}
+		}
+	}
+
+	BUG_ON(!res);
+	return res;
+}
+
+/*
+ * Return the cgroup for "task" from the given hierarchy. Must be
+ * called with cgroup_mutex and css_set_lock held.
+ */
+struct cgroup *task_cgroup_from_root(struct task_struct *task,
+				     struct cgroup_root *root)
+{
+	/*
+	 * No need to lock the task - since we hold cgroup_mutex the
+	 * task can't change groups, so the only thing that can happen
+	 * is that it exits and its css is set back to init_css_set.
+	 */
+	return cset_cgroup_from_root(task_css_set(task), root);
+}
+
+/*
+ * A task must hold cgroup_mutex to modify cgroups.
+ *
+ * Any task can increment and decrement the count field without lock.
+ * So in general, code holding cgroup_mutex can't rely on the count
+ * field not changing.  However, if the count goes to zero, then only
+ * cgroup_attach_task() can increment it again.  Because a count of zero
+ * means that no tasks are currently attached, therefore there is no
+ * way a task attached to that cgroup can fork (the other way to
+ * increment the count).  So code holding cgroup_mutex can safely
+ * assume that if the count is zero, it will stay zero. Similarly, if
+ * a task holds cgroup_mutex on a cgroup with zero count, it
+ * knows that the cgroup won't be removed, as cgroup_rmdir()
+ * needs that mutex.
+ *
+ * A cgroup can only be deleted if both its 'count' of using tasks
+ * is zero, and its list of 'children' cgroups is empty.  Since all
+ * tasks in the system use _some_ cgroup, and since there is always at
+ * least one task in the system (init, pid == 1), therefore, root cgroup
+ * always has either children cgroups and/or using tasks.  So we don't
+ * need a special hack to ensure that root cgroup cannot be deleted.
+ *
+ * P.S.  One more locking exception.  RCU is used to guard the
+ * update of a tasks cgroup pointer by cgroup_attach_task()
+ */
+
+static struct kernfs_syscall_ops cgroup_kf_syscall_ops;
+
+static char *cgroup_file_name(struct cgroup *cgrp, const struct cftype *cft,
+			      char *buf)
+{
+	struct cgroup_subsys *ss = cft->ss;
+
+	if (cft->ss && !(cft->flags & CFTYPE_NO_PREFIX) &&
+	    !(cgrp->root->flags & CGRP_ROOT_NOPREFIX))
+		snprintf(buf, CGROUP_FILE_NAME_MAX, "%s.%s",
+			 cgroup_on_dfl(cgrp) ? ss->name : ss->legacy_name,
+			 cft->name);
+	else
+		strscpy(buf, cft->name, CGROUP_FILE_NAME_MAX);
+	return buf;
+}
+
+/**
+ * cgroup_file_mode - deduce file mode of a control file
+ * @cft: the control file in question
+ *
+ * S_IRUGO for read, S_IWUSR for write.
+ */
+static umode_t cgroup_file_mode(const struct cftype *cft)
+{
+	umode_t mode = 0;
+
+	if (cft->read_u64 || cft->read_s64 || cft->seq_show)
+		mode |= S_IRUGO;
+
+	if (cft->write_u64 || cft->write_s64 || cft->write) {
+		if (cft->flags & CFTYPE_WORLD_WRITABLE)
+			mode |= S_IWUGO;
+		else
+			mode |= S_IWUSR;
+	}
+
+	return mode;
+}
+
+/**
+ * cgroup_calc_subtree_ss_mask - calculate subtree_ss_mask
+ * @subtree_control: the new subtree_control mask to consider
+ * @this_ss_mask: available subsystems
+ *
+ * On the default hierarchy, a subsystem may request other subsystems to be
+ * enabled together through its ->depends_on mask.  In such cases, more
+ * subsystems than specified in "cgroup.subtree_control" may be enabled.
+ *
+ * This function calculates which subsystems need to be enabled if
+ * @subtree_control is to be applied while restricted to @this_ss_mask.
+ */
+static u16 cgroup_calc_subtree_ss_mask(u16 subtree_control, u16 this_ss_mask)
+{
+	u16 cur_ss_mask = subtree_control;
+	struct cgroup_subsys *ss;
+	int ssid;
+
+	lockdep_assert_held(&cgroup_mutex);
+
+	cur_ss_mask |= cgrp_dfl_implicit_ss_mask;
+
+	while (true) {
+		u16 new_ss_mask = cur_ss_mask;
+
+		do_each_subsys_mask(ss, ssid, cur_ss_mask) {
+			new_ss_mask |= ss->depends_on;
+		} while_each_subsys_mask();
+
+		/*
+		 * Mask out subsystems which aren't available.  This can
+		 * happen only if some depended-upon subsystems were bound
+		 * to non-default hierarchies.
+		 */
+		new_ss_mask &= this_ss_mask;
+
+		if (new_ss_mask == cur_ss_mask)
+			break;
+		cur_ss_mask = new_ss_mask;
+	}
+
+	return cur_ss_mask;
+}
+
+/**
+ * cgroup_kn_unlock - unlocking helper for cgroup kernfs methods
+ * @kn: the kernfs_node being serviced
+ *
+ * This helper undoes cgroup_kn_lock_live() and should be invoked before
+ * the method finishes if locking succeeded.  Note that once this function
+ * returns the cgroup returned by cgroup_kn_lock_live() may become
+ * inaccessible any time.  If the caller intends to continue to access the
+ * cgroup, it should pin it before invoking this function.
+ */
+void cgroup_kn_unlock(struct kernfs_node *kn)
+{
+	struct cgroup *cgrp;
+
+	if (kernfs_type(kn) == KERNFS_DIR)
+		cgrp = kn->priv;
+	else
+		cgrp = kn->parent->priv;
+
+	mutex_unlock(&cgroup_mutex);
+
+	kernfs_unbreak_active_protection(kn);
+	cgroup_put(cgrp);
+}
+
+/**
+ * cgroup_kn_lock_live - locking helper for cgroup kernfs methods
+ * @kn: the kernfs_node being serviced
+ * @drain_offline: perform offline draining on the cgroup
+ *
+ * This helper is to be used by a cgroup kernfs method currently servicing
+ * @kn.  It breaks the active protection, performs cgroup locking and
+ * verifies that the associated cgroup is alive.  Returns the cgroup if
+ * alive; otherwise, %NULL.  A successful return should be undone by a
+ * matching cgroup_kn_unlock() invocation.  If @drain_offline is %true, the
+ * cgroup is drained of offlining csses before return.
+ *
+ * Any cgroup kernfs method implementation which requires locking the
+ * associated cgroup should use this helper.  It avoids nesting cgroup
+ * locking under kernfs active protection and allows all kernfs operations
+ * including self-removal.
+ */
+struct cgroup *cgroup_kn_lock_live(struct kernfs_node *kn, bool drain_offline)
+{
+	struct cgroup *cgrp;
+
+	if (kernfs_type(kn) == KERNFS_DIR)
+		cgrp = kn->priv;
+	else
+		cgrp = kn->parent->priv;
+
+	/*
+	 * We're gonna grab cgroup_mutex which nests outside kernfs
+	 * active_ref.  cgroup liveliness check alone provides enough
+	 * protection against removal.  Ensure @cgrp stays accessible and
+	 * break the active_ref protection.
+	 */
+	if (!cgroup_tryget(cgrp))
+		return NULL;
+	kernfs_break_active_protection(kn);
+
+	if (drain_offline)
+		cgroup_lock_and_drain_offline(cgrp);
+	else
+		mutex_lock(&cgroup_mutex);
+
+	if (!cgroup_is_dead(cgrp))
+		return cgrp;
+
+	cgroup_kn_unlock(kn);
+	return NULL;
+}
+
+static void cgroup_rm_file(struct cgroup *cgrp, const struct cftype *cft)
+{
+	char name[CGROUP_FILE_NAME_MAX];
+
+	lockdep_assert_held(&cgroup_mutex);
+
+	if (cft->file_offset) {
+		struct cgroup_subsys_state *css = cgroup_css(cgrp, cft->ss);
+		struct cgroup_file *cfile = (void *)css + cft->file_offset;
+
+		spin_lock_irq(&cgroup_file_kn_lock);
+		cfile->kn = NULL;
+		spin_unlock_irq(&cgroup_file_kn_lock);
+
+		del_timer_sync(&cfile->notify_timer);
+	}
+
+	kernfs_remove_by_name(cgrp->kn, cgroup_file_name(cgrp, cft, name));
+}
+
+/**
+ * css_clear_dir - remove subsys files in a cgroup directory
+ * @css: taget css
+ */
+static void css_clear_dir(struct cgroup_subsys_state *css)
+{
+	struct cgroup *cgrp = css->cgroup;
+	struct cftype *cfts;
+
+	if (!(css->flags & CSS_VISIBLE))
+		return;
+
+	css->flags &= ~CSS_VISIBLE;
+
+	if (!css->ss) {
+		if (cgroup_on_dfl(cgrp))
+			cfts = cgroup_base_files;
+		else
+			cfts = cgroup1_base_files;
+
+		cgroup_addrm_files(css, cgrp, cfts, false);
+	} else {
+		list_for_each_entry(cfts, &css->ss->cfts, node)
+			cgroup_addrm_files(css, cgrp, cfts, false);
+	}
+}
+
+/**
+ * css_populate_dir - create subsys files in a cgroup directory
+ * @css: target css
+ *
+ * On failure, no file is added.
+ */
+static int css_populate_dir(struct cgroup_subsys_state *css)
+{
+	struct cgroup *cgrp = css->cgroup;
+	struct cftype *cfts, *failed_cfts;
+	int ret;
+
+	if ((css->flags & CSS_VISIBLE) || !cgrp->kn)
+		return 0;
+
+	if (!css->ss) {
+		if (cgroup_on_dfl(cgrp))
+			cfts = cgroup_base_files;
+		else
+			cfts = cgroup1_base_files;
+
+		ret = cgroup_addrm_files(&cgrp->self, cgrp, cfts, true);
+		if (ret < 0)
+			return ret;
+	} else {
+		list_for_each_entry(cfts, &css->ss->cfts, node) {
+			ret = cgroup_addrm_files(css, cgrp, cfts, true);
+			if (ret < 0) {
+				failed_cfts = cfts;
+				goto err;
+			}
+		}
+	}
+
+	css->flags |= CSS_VISIBLE;
+
+	return 0;
+err:
+	list_for_each_entry(cfts, &css->ss->cfts, node) {
+		if (cfts == failed_cfts)
+			break;
+		cgroup_addrm_files(css, cgrp, cfts, false);
+	}
+	return ret;
+}
+
+int rebind_subsystems(struct cgroup_root *dst_root, u16 ss_mask)
+{
+	struct cgroup *dcgrp = &dst_root->cgrp;
+	struct cgroup_subsys *ss;
+	int ssid, i, ret;
+	u16 dfl_disable_ss_mask = 0;
+
+	lockdep_assert_held(&cgroup_mutex);
+
+	do_each_subsys_mask(ss, ssid, ss_mask) {
+		/*
+		 * If @ss has non-root csses attached to it, can't move.
+		 * If @ss is an implicit controller, it is exempt from this
+		 * rule and can be stolen.
+		 */
+		if (css_next_child(NULL, cgroup_css(&ss->root->cgrp, ss)) &&
+		    !ss->implicit_on_dfl)
+			return -EBUSY;
+
+		/* can't move between two non-dummy roots either */
+		if (ss->root != &cgrp_dfl_root && dst_root != &cgrp_dfl_root)
+			return -EBUSY;
+
+		/*
+		 * Collect ssid's that need to be disabled from default
+		 * hierarchy.
+		 */
+		if (ss->root == &cgrp_dfl_root)
+			dfl_disable_ss_mask |= 1 << ssid;
+
+	} while_each_subsys_mask();
+
+	if (dfl_disable_ss_mask) {
+		struct cgroup *scgrp = &cgrp_dfl_root.cgrp;
+
+		/*
+		 * Controllers from default hierarchy that need to be rebound
+		 * are all disabled together in one go.
+		 */
+		cgrp_dfl_root.subsys_mask &= ~dfl_disable_ss_mask;
+		WARN_ON(cgroup_apply_control(scgrp));
+		cgroup_finalize_control(scgrp, 0);
+	}
+
+	do_each_subsys_mask(ss, ssid, ss_mask) {
+		struct cgroup_root *src_root = ss->root;
+		struct cgroup *scgrp = &src_root->cgrp;
+		struct cgroup_subsys_state *css = cgroup_css(scgrp, ss);
+		struct css_set *cset;
+
+		WARN_ON(!css || cgroup_css(dcgrp, ss));
+
+		if (src_root != &cgrp_dfl_root) {
+			/* disable from the source */
+			src_root->subsys_mask &= ~(1 << ssid);
+			WARN_ON(cgroup_apply_control(scgrp));
+			cgroup_finalize_control(scgrp, 0);
+		}
+
+		/* rebind */
+		RCU_INIT_POINTER(scgrp->subsys[ssid], NULL);
+		rcu_assign_pointer(dcgrp->subsys[ssid], css);
+		ss->root = dst_root;
+		css->cgroup = dcgrp;
+
+		spin_lock_irq(&css_set_lock);
+		hash_for_each(css_set_table, i, cset, hlist)
+			list_move_tail(&cset->e_cset_node[ss->id],
+				       &dcgrp->e_csets[ss->id]);
+		spin_unlock_irq(&css_set_lock);
+
+		/* default hierarchy doesn't enable controllers by default */
+		dst_root->subsys_mask |= 1 << ssid;
+		if (dst_root == &cgrp_dfl_root) {
+			static_branch_enable(cgroup_subsys_on_dfl_key[ssid]);
+		} else {
+			dcgrp->subtree_control |= 1 << ssid;
+			static_branch_disable(cgroup_subsys_on_dfl_key[ssid]);
+		}
+
+		ret = cgroup_apply_control(dcgrp);
+		if (ret)
+			pr_warn("partial failure to rebind %s controller (err=%d)\n",
+				ss->name, ret);
+
+		if (ss->bind)
+			ss->bind(css);
+	} while_each_subsys_mask();
+
+	kernfs_activate(dcgrp->kn);
+	return 0;
+}
+
+int cgroup_show_path(struct seq_file *sf, struct kernfs_node *kf_node,
+		     struct kernfs_root *kf_root)
+{
+	int len = 0;
+	char *buf = NULL;
+	struct cgroup_root *kf_cgroot = cgroup_root_from_kf(kf_root);
+	struct cgroup *ns_cgroup;
+
+	buf = kmalloc(PATH_MAX, GFP_KERNEL);
+	if (!buf)
+		return -ENOMEM;
+
+	spin_lock_irq(&css_set_lock);
+	ns_cgroup = current_cgns_cgroup_from_root(kf_cgroot);
+	len = kernfs_path_from_node(kf_node, ns_cgroup->kn, buf, PATH_MAX);
+	spin_unlock_irq(&css_set_lock);
+
+	if (len >= PATH_MAX)
+		len = -ERANGE;
+	else if (len > 0) {
+		seq_escape(sf, buf, " \t\n\\");
+		len = 0;
+	}
+	kfree(buf);
+	return len;
+}
+
+static int parse_cgroup_root_flags(char *data, unsigned int *root_flags)
+{
+	char *token;
+
+	*root_flags = 0;
+
+	if (!data || *data == '\0')
+		return 0;
+
+	while ((token = strsep(&data, ",")) != NULL) {
+		if (!strcmp(token, "nsdelegate")) {
+			*root_flags |= CGRP_ROOT_NS_DELEGATE;
+			continue;
+		}
+
+		pr_err("cgroup2: unknown option \"%s\"\n", token);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static void apply_cgroup_root_flags(unsigned int root_flags)
+{
+	if (current->nsproxy->cgroup_ns == &init_cgroup_ns) {
+		if (root_flags & CGRP_ROOT_NS_DELEGATE)
+			cgrp_dfl_root.flags |= CGRP_ROOT_NS_DELEGATE;
+		else
+			cgrp_dfl_root.flags &= ~CGRP_ROOT_NS_DELEGATE;
+	}
+}
+
+static int cgroup_show_options(struct seq_file *seq, struct kernfs_root *kf_root)
+{
+	if (cgrp_dfl_root.flags & CGRP_ROOT_NS_DELEGATE)
+		seq_puts(seq, ",nsdelegate");
+	return 0;
+}
+
+static int cgroup_remount(struct kernfs_root *kf_root, int *flags, char *data)
+{
+	unsigned int root_flags;
+	int ret;
+
+	ret = parse_cgroup_root_flags(data, &root_flags);
+	if (ret)
+		return ret;
+
+	apply_cgroup_root_flags(root_flags);
+	return 0;
+}
+
+/*
+ * To reduce the fork() overhead for systems that are not actually using
+ * their cgroups capability, we don't maintain the lists running through
+ * each css_set to its tasks until we see the list actually used - in other
+ * words after the first mount.
+ */
+static bool use_task_css_set_links __read_mostly;
+
+static void cgroup_enable_task_cg_lists(void)
+{
+	struct task_struct *p, *g;
+
+	/*
+	 * We need tasklist_lock because RCU is not safe against
+	 * while_each_thread(). Besides, a forking task that has passed
+	 * cgroup_post_fork() without seeing use_task_css_set_links = 1
+	 * is not guaranteed to have its child immediately visible in the
+	 * tasklist if we walk through it with RCU.
+	 */
+	read_lock(&tasklist_lock);
+	spin_lock_irq(&css_set_lock);
+
+	if (use_task_css_set_links)
+		goto out_unlock;
+
+	use_task_css_set_links = true;
+
+	do_each_thread(g, p) {
+		WARN_ON_ONCE(!list_empty(&p->cg_list) ||
+			     task_css_set(p) != &init_css_set);
+
+		/*
+		 * We should check if the process is exiting, otherwise
+		 * it will race with cgroup_exit() in that the list
+		 * entry won't be deleted though the process has exited.
+		 * Do it while holding siglock so that we don't end up
+		 * racing against cgroup_exit().
+		 *
+		 * Interrupts were already disabled while acquiring
+		 * the css_set_lock, so we do not need to disable it
+		 * again when acquiring the sighand->siglock here.
+		 */
+		spin_lock(&p->sighand->siglock);
+		if (!(p->flags & PF_EXITING)) {
+			struct css_set *cset = task_css_set(p);
+
+			if (!css_set_populated(cset))
+				css_set_update_populated(cset, true);
+			list_add_tail(&p->cg_list, &cset->tasks);
+			get_css_set(cset);
+			cset->nr_tasks++;
+		}
+		spin_unlock(&p->sighand->siglock);
+	} while_each_thread(g, p);
+out_unlock:
+	spin_unlock_irq(&css_set_lock);
+	read_unlock(&tasklist_lock);
+}
+
+static void init_cgroup_housekeeping(struct cgroup *cgrp)
+{
+	struct cgroup_subsys *ss;
+	int ssid;
+
+	INIT_LIST_HEAD(&cgrp->self.sibling);
+	INIT_LIST_HEAD(&cgrp->self.children);
+	INIT_LIST_HEAD(&cgrp->cset_links);
+	INIT_LIST_HEAD(&cgrp->pidlists);
+	mutex_init(&cgrp->pidlist_mutex);
+	cgrp->self.cgroup = cgrp;
+	cgrp->self.flags |= CSS_ONLINE;
+	cgrp->dom_cgrp = cgrp;
+	cgrp->max_descendants = INT_MAX;
+	cgrp->max_depth = INT_MAX;
+	INIT_LIST_HEAD(&cgrp->rstat_css_list);
+	prev_cputime_init(&cgrp->prev_cputime);
+
+	for_each_subsys(ss, ssid)
+		INIT_LIST_HEAD(&cgrp->e_csets[ssid]);
+
+	init_waitqueue_head(&cgrp->offline_waitq);
+	INIT_WORK(&cgrp->release_agent_work, cgroup1_release_agent);
+}
+
+void init_cgroup_root(struct cgroup_root *root, struct cgroup_sb_opts *opts)
+{
+	struct cgroup *cgrp = &root->cgrp;
+
+	INIT_LIST_HEAD(&root->root_list);
+	atomic_set(&root->nr_cgrps, 1);
+	cgrp->root = root;
+	init_cgroup_housekeeping(cgrp);
+	idr_init(&root->cgroup_idr);
+
+	root->flags = opts->flags;
+	if (opts->release_agent)
+		strscpy(root->release_agent_path, opts->release_agent, PATH_MAX);
+	if (opts->name)
+		strscpy(root->name, opts->name, MAX_CGROUP_ROOT_NAMELEN);
+	if (opts->cpuset_clone_children)
+		set_bit(CGRP_CPUSET_CLONE_CHILDREN, &root->cgrp.flags);
+}
+
+int cgroup_setup_root(struct cgroup_root *root, u16 ss_mask, int ref_flags)
+{
+	LIST_HEAD(tmp_links);
+	struct cgroup *root_cgrp = &root->cgrp;
+	struct kernfs_syscall_ops *kf_sops;
+	struct css_set *cset;
+	int i, ret;
+
+	lockdep_assert_held(&cgroup_mutex);
+
+	ret = cgroup_idr_alloc(&root->cgroup_idr, root_cgrp, 1, 2, GFP_KERNEL);
+	if (ret < 0)
+		goto out;
+	root_cgrp->id = ret;
+	root_cgrp->ancestor_ids[0] = ret;
+
+	ret = percpu_ref_init(&root_cgrp->self.refcnt, css_release,
+			      ref_flags, GFP_KERNEL);
+	if (ret)
+		goto out;
+
+	/*
+	 * We're accessing css_set_count without locking css_set_lock here,
+	 * but that's OK - it can only be increased by someone holding
+	 * cgroup_lock, and that's us.  Later rebinding may disable
+	 * controllers on the default hierarchy and thus create new csets,
+	 * which can't be more than the existing ones.  Allocate 2x.
+	 */
+	ret = allocate_cgrp_cset_links(2 * css_set_count, &tmp_links);
+	if (ret)
+		goto cancel_ref;
+
+	ret = cgroup_init_root_id(root);
+	if (ret)
+		goto cancel_ref;
+
+	kf_sops = root == &cgrp_dfl_root ?
+		&cgroup_kf_syscall_ops : &cgroup1_kf_syscall_ops;
+
+	root->kf_root = kernfs_create_root(kf_sops,
+					   KERNFS_ROOT_CREATE_DEACTIVATED |
+					   KERNFS_ROOT_SUPPORT_EXPORTOP,
+					   root_cgrp);
+	if (IS_ERR(root->kf_root)) {
+		ret = PTR_ERR(root->kf_root);
+		goto exit_root_id;
+	}
+	root_cgrp->kn = root->kf_root->kn;
+
+	ret = css_populate_dir(&root_cgrp->self);
+	if (ret)
+		goto destroy_root;
+
+	ret = rebind_subsystems(root, ss_mask);
+	if (ret)
+		goto destroy_root;
+
+	ret = cgroup_bpf_inherit(root_cgrp);
+	WARN_ON_ONCE(ret);
+
+	trace_cgroup_setup_root(root);
+
+	/*
+	 * There must be no failure case after here, since rebinding takes
+	 * care of subsystems' refcounts, which are explicitly dropped in
+	 * the failure exit path.
+	 */
+	list_add(&root->root_list, &cgroup_roots);
+	cgroup_root_count++;
+
+	/*
+	 * Link the root cgroup in this hierarchy into all the css_set
+	 * objects.
+	 */
+	spin_lock_irq(&css_set_lock);
+	hash_for_each(css_set_table, i, cset, hlist) {
+		link_css_set(&tmp_links, cset, root_cgrp);
+		if (css_set_populated(cset))
+			cgroup_update_populated(root_cgrp, true);
+	}
+	spin_unlock_irq(&css_set_lock);
+
+	BUG_ON(!list_empty(&root_cgrp->self.children));
+	BUG_ON(atomic_read(&root->nr_cgrps) != 1);
+
+	kernfs_activate(root_cgrp->kn);
+	ret = 0;
+	goto out;
+
+destroy_root:
+	kernfs_destroy_root(root->kf_root);
+	root->kf_root = NULL;
+exit_root_id:
+	cgroup_exit_root_id(root);
+cancel_ref:
+	percpu_ref_exit(&root_cgrp->self.refcnt);
+out:
+	free_cgrp_cset_links(&tmp_links);
+	return ret;
+}
+
+struct dentry *cgroup_do_mount(struct file_system_type *fs_type, int flags,
+			       struct cgroup_root *root, unsigned long magic,
+			       struct cgroup_namespace *ns)
+{
+	struct dentry *dentry;
+	bool new_sb = false;
+
+	dentry = kernfs_mount(fs_type, flags, root->kf_root, magic, &new_sb);
+
+	/*
+	 * In non-init cgroup namespace, instead of root cgroup's dentry,
+	 * we return the dentry corresponding to the cgroupns->root_cgrp.
+	 */
+	if (!IS_ERR(dentry) && ns != &init_cgroup_ns) {
+		struct dentry *nsdentry;
+		struct super_block *sb = dentry->d_sb;
+		struct cgroup *cgrp;
+
+		mutex_lock(&cgroup_mutex);
+		spin_lock_irq(&css_set_lock);
+
+		cgrp = cset_cgroup_from_root(ns->root_cset, root);
+
+		spin_unlock_irq(&css_set_lock);
+		mutex_unlock(&cgroup_mutex);
+
+		nsdentry = kernfs_node_dentry(cgrp->kn, sb);
+		dput(dentry);
+		if (IS_ERR(nsdentry))
+			deactivate_locked_super(sb);
+		dentry = nsdentry;
+	}
+
+	if (!new_sb)
+		cgroup_put(&root->cgrp);
+
+	return dentry;
+}
+
+static struct dentry *cgroup_mount(struct file_system_type *fs_type,
+			 int flags, const char *unused_dev_name,
+			 void *data)
+{
+	struct cgroup_namespace *ns = current->nsproxy->cgroup_ns;
+	struct dentry *dentry;
+	int ret;
+
+	get_cgroup_ns(ns);
+
+	/* Check if the caller has permission to mount. */
+	if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN)) {
+		put_cgroup_ns(ns);
+		return ERR_PTR(-EPERM);
+	}
+
+	/*
+	 * The first time anyone tries to mount a cgroup, enable the list
+	 * linking each css_set to its tasks and fix up all existing tasks.
+	 */
+	if (!use_task_css_set_links)
+		cgroup_enable_task_cg_lists();
+
+	if (fs_type == &cgroup2_fs_type) {
+		unsigned int root_flags;
+
+		ret = parse_cgroup_root_flags(data, &root_flags);
+		if (ret) {
+			put_cgroup_ns(ns);
+			return ERR_PTR(ret);
+		}
+
+		cgrp_dfl_visible = true;
+		cgroup_get_live(&cgrp_dfl_root.cgrp);
+
+		dentry = cgroup_do_mount(&cgroup2_fs_type, flags, &cgrp_dfl_root,
+					 CGROUP2_SUPER_MAGIC, ns);
+		if (!IS_ERR(dentry))
+			apply_cgroup_root_flags(root_flags);
+	} else {
+		dentry = cgroup1_mount(&cgroup_fs_type, flags, data,
+				       CGROUP_SUPER_MAGIC, ns);
+	}
+
+	put_cgroup_ns(ns);
+	return dentry;
+}
+
+static void cgroup_kill_sb(struct super_block *sb)
+{
+	struct kernfs_root *kf_root = kernfs_root_from_sb(sb);
+	struct cgroup_root *root = cgroup_root_from_kf(kf_root);
+
+	/*
+	 * If @root doesn't have any mounts or children, start killing it.
+	 * This prevents new mounts by disabling percpu_ref_tryget_live().
+	 * cgroup_mount() may wait for @root's release.
+	 *
+	 * And don't kill the default root.
+	 */
+	if (!list_empty(&root->cgrp.self.children) ||
+	    root == &cgrp_dfl_root)
+		cgroup_put(&root->cgrp);
+	else
+		percpu_ref_kill(&root->cgrp.self.refcnt);
+
+	kernfs_kill_sb(sb);
+}
+
+struct file_system_type cgroup_fs_type = {
+	.name = "cgroup",
+	.mount = cgroup_mount,
+	.kill_sb = cgroup_kill_sb,
+	.fs_flags = FS_USERNS_MOUNT,
+};
+
+static struct file_system_type cgroup2_fs_type = {
+	.name = "cgroup2",
+	.mount = cgroup_mount,
+	.kill_sb = cgroup_kill_sb,
+	.fs_flags = FS_USERNS_MOUNT,
+};
+
+int cgroup_path_ns_locked(struct cgroup *cgrp, char *buf, size_t buflen,
+			  struct cgroup_namespace *ns)
+{
+	struct cgroup *root = cset_cgroup_from_root(ns->root_cset, cgrp->root);
+
+	return kernfs_path_from_node(cgrp->kn, root->kn, buf, buflen);
+}
+
+int cgroup_path_ns(struct cgroup *cgrp, char *buf, size_t buflen,
+		   struct cgroup_namespace *ns)
+{
+	int ret;
+
+	mutex_lock(&cgroup_mutex);
+	spin_lock_irq(&css_set_lock);
+
+	ret = cgroup_path_ns_locked(cgrp, buf, buflen, ns);
+
+	spin_unlock_irq(&css_set_lock);
+	mutex_unlock(&cgroup_mutex);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(cgroup_path_ns);
+
+/**
+ * task_cgroup_path - cgroup path of a task in the first cgroup hierarchy
+ * @task: target task
+ * @buf: the buffer to write the path into
+ * @buflen: the length of the buffer
+ *
+ * Determine @task's cgroup on the first (the one with the lowest non-zero
+ * hierarchy_id) cgroup hierarchy and copy its path into @buf.  This
+ * function grabs cgroup_mutex and shouldn't be used inside locks used by
+ * cgroup controller callbacks.
+ *
+ * Return value is the same as kernfs_path().
+ */
+int task_cgroup_path(struct task_struct *task, char *buf, size_t buflen)
+{
+	struct cgroup_root *root;
+	struct cgroup *cgrp;
+	int hierarchy_id = 1;
+	int ret;
+
+	mutex_lock(&cgroup_mutex);
+	spin_lock_irq(&css_set_lock);
+
+	root = idr_get_next(&cgroup_hierarchy_idr, &hierarchy_id);
+
+	if (root) {
+		cgrp = task_cgroup_from_root(task, root);
+		ret = cgroup_path_ns_locked(cgrp, buf, buflen, &init_cgroup_ns);
+	} else {
+		/* if no hierarchy exists, everyone is in "/" */
+		ret = strlcpy(buf, "/", buflen);
+	}
+
+	spin_unlock_irq(&css_set_lock);
+	mutex_unlock(&cgroup_mutex);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(task_cgroup_path);
+
+/**
+ * cgroup_migrate_add_task - add a migration target task to a migration context
+ * @task: target task
+ * @mgctx: target migration context
+ *
+ * Add @task, which is a migration target, to @mgctx->tset.  This function
+ * becomes noop if @task doesn't need to be migrated.  @task's css_set
+ * should have been added as a migration source and @task->cg_list will be
+ * moved from the css_set's tasks list to mg_tasks one.
+ */
+static void cgroup_migrate_add_task(struct task_struct *task,
+				    struct cgroup_mgctx *mgctx)
+{
+	struct css_set *cset;
+
+	lockdep_assert_held(&css_set_lock);
+
+	/* @task either already exited or can't exit until the end */
+	if (task->flags & PF_EXITING)
+		return;
+
+	/* leave @task alone if post_fork() hasn't linked it yet */
+	if (list_empty(&task->cg_list))
+		return;
+
+	cset = task_css_set(task);
+	if (!cset->mg_src_cgrp)
+		return;
+
+	mgctx->tset.nr_tasks++;
+
+	list_move_tail(&task->cg_list, &cset->mg_tasks);
+	if (list_empty(&cset->mg_node))
+		list_add_tail(&cset->mg_node,
+			      &mgctx->tset.src_csets);
+	if (list_empty(&cset->mg_dst_cset->mg_node))
+		list_add_tail(&cset->mg_dst_cset->mg_node,
+			      &mgctx->tset.dst_csets);
+}
+
+/**
+ * cgroup_taskset_first - reset taskset and return the first task
+ * @tset: taskset of interest
+ * @dst_cssp: output variable for the destination css
+ *
+ * @tset iteration is initialized and the first task is returned.
+ */
+struct task_struct *cgroup_taskset_first(struct cgroup_taskset *tset,
+					 struct cgroup_subsys_state **dst_cssp)
+{
+	tset->cur_cset = list_first_entry(tset->csets, struct css_set, mg_node);
+	tset->cur_task = NULL;
+
+	return cgroup_taskset_next(tset, dst_cssp);
+}
+
+/**
+ * cgroup_taskset_next - iterate to the next task in taskset
+ * @tset: taskset of interest
+ * @dst_cssp: output variable for the destination css
+ *
+ * Return the next task in @tset.  Iteration must have been initialized
+ * with cgroup_taskset_first().
+ */
+struct task_struct *cgroup_taskset_next(struct cgroup_taskset *tset,
+					struct cgroup_subsys_state **dst_cssp)
+{
+	struct css_set *cset = tset->cur_cset;
+	struct task_struct *task = tset->cur_task;
+
+	while (&cset->mg_node != tset->csets) {
+		if (!task)
+			task = list_first_entry(&cset->mg_tasks,
+						struct task_struct, cg_list);
+		else
+			task = list_next_entry(task, cg_list);
+
+		if (&task->cg_list != &cset->mg_tasks) {
+			tset->cur_cset = cset;
+			tset->cur_task = task;
+
+			/*
+			 * This function may be called both before and
+			 * after cgroup_taskset_migrate().  The two cases
+			 * can be distinguished by looking at whether @cset
+			 * has its ->mg_dst_cset set.
+			 */
+			if (cset->mg_dst_cset)
+				*dst_cssp = cset->mg_dst_cset->subsys[tset->ssid];
+			else
+				*dst_cssp = cset->subsys[tset->ssid];
+
+			return task;
+		}
+
+		cset = list_next_entry(cset, mg_node);
+		task = NULL;
+	}
+
+	return NULL;
+}
+
+/**
+ * cgroup_taskset_migrate - migrate a taskset
+ * @mgctx: migration context
+ *
+ * Migrate tasks in @mgctx as setup by migration preparation functions.
+ * This function fails iff one of the ->can_attach callbacks fails and
+ * guarantees that either all or none of the tasks in @mgctx are migrated.
+ * @mgctx is consumed regardless of success.
+ */
+static int cgroup_migrate_execute(struct cgroup_mgctx *mgctx)
+{
+	struct cgroup_taskset *tset = &mgctx->tset;
+	struct cgroup_subsys *ss;
+	struct task_struct *task, *tmp_task;
+	struct css_set *cset, *tmp_cset;
+	int ssid, failed_ssid, ret;
+
+	/* check that we can legitimately attach to the cgroup */
+	if (tset->nr_tasks) {
+		do_each_subsys_mask(ss, ssid, mgctx->ss_mask) {
+			if (ss->can_attach) {
+				tset->ssid = ssid;
+				ret = ss->can_attach(tset);
+				if (ret) {
+					failed_ssid = ssid;
+					goto out_cancel_attach;
+				}
+			}
+		} while_each_subsys_mask();
+	}
+
+	/*
+	 * Now that we're guaranteed success, proceed to move all tasks to
+	 * the new cgroup.  There are no failure cases after here, so this
+	 * is the commit point.
+	 */
+	spin_lock_irq(&css_set_lock);
+	list_for_each_entry(cset, &tset->src_csets, mg_node) {
+		list_for_each_entry_safe(task, tmp_task, &cset->mg_tasks, cg_list) {
+			struct css_set *from_cset = task_css_set(task);
+			struct css_set *to_cset = cset->mg_dst_cset;
+
+			get_css_set(to_cset);
+			to_cset->nr_tasks++;
+			css_set_move_task(task, from_cset, to_cset, true);
+			put_css_set_locked(from_cset);
+			from_cset->nr_tasks--;
+		}
+	}
+	spin_unlock_irq(&css_set_lock);
+
+	/*
+	 * Migration is committed, all target tasks are now on dst_csets.
+	 * Nothing is sensitive to fork() after this point.  Notify
+	 * controllers that migration is complete.
+	 */
+	tset->csets = &tset->dst_csets;
+
+	if (tset->nr_tasks) {
+		do_each_subsys_mask(ss, ssid, mgctx->ss_mask) {
+			if (ss->attach) {
+				tset->ssid = ssid;
+				ss->attach(tset);
+			}
+		} while_each_subsys_mask();
+	}
+
+	ret = 0;
+	goto out_release_tset;
+
+out_cancel_attach:
+	if (tset->nr_tasks) {
+		do_each_subsys_mask(ss, ssid, mgctx->ss_mask) {
+			if (ssid == failed_ssid)
+				break;
+			if (ss->cancel_attach) {
+				tset->ssid = ssid;
+				ss->cancel_attach(tset);
+			}
+		} while_each_subsys_mask();
+	}
+out_release_tset:
+	spin_lock_irq(&css_set_lock);
+	list_splice_init(&tset->dst_csets, &tset->src_csets);
+	list_for_each_entry_safe(cset, tmp_cset, &tset->src_csets, mg_node) {
+		list_splice_tail_init(&cset->mg_tasks, &cset->tasks);
+		list_del_init(&cset->mg_node);
+	}
+	spin_unlock_irq(&css_set_lock);
+
+	/*
+	 * Re-initialize the cgroup_taskset structure in case it is reused
+	 * again in another cgroup_migrate_add_task()/cgroup_migrate_execute()
+	 * iteration.
+	 */
+	tset->nr_tasks = 0;
+	tset->csets    = &tset->src_csets;
+	return ret;
+}
+
+/**
+ * cgroup_migrate_vet_dst - verify whether a cgroup can be migration destination
+ * @dst_cgrp: destination cgroup to test
+ *
+ * On the default hierarchy, except for the mixable, (possible) thread root
+ * and threaded cgroups, subtree_control must be zero for migration
+ * destination cgroups with tasks so that child cgroups don't compete
+ * against tasks.
+ */
+int cgroup_migrate_vet_dst(struct cgroup *dst_cgrp)
+{
+	/* v1 doesn't have any restriction */
+	if (!cgroup_on_dfl(dst_cgrp))
+		return 0;
+
+	/* verify @dst_cgrp can host resources */
+	if (!cgroup_is_valid_domain(dst_cgrp->dom_cgrp))
+		return -EOPNOTSUPP;
+
+	/* mixables don't care */
+	if (cgroup_is_mixable(dst_cgrp))
+		return 0;
+
+	/*
+	 * If @dst_cgrp is already or can become a thread root or is
+	 * threaded, it doesn't matter.
+	 */
+	if (cgroup_can_be_thread_root(dst_cgrp) || cgroup_is_threaded(dst_cgrp))
+		return 0;
+
+	/* apply no-internal-process constraint */
+	if (dst_cgrp->subtree_control)
+		return -EBUSY;
+
+	return 0;
+}
+
+/**
+ * cgroup_migrate_finish - cleanup after attach
+ * @mgctx: migration context
+ *
+ * Undo cgroup_migrate_add_src() and cgroup_migrate_prepare_dst().  See
+ * those functions for details.
+ */
+void cgroup_migrate_finish(struct cgroup_mgctx *mgctx)
+{
+	LIST_HEAD(preloaded);
+	struct css_set *cset, *tmp_cset;
+
+	lockdep_assert_held(&cgroup_mutex);
+
+	spin_lock_irq(&css_set_lock);
+
+	list_splice_tail_init(&mgctx->preloaded_src_csets, &preloaded);
+	list_splice_tail_init(&mgctx->preloaded_dst_csets, &preloaded);
+
+	list_for_each_entry_safe(cset, tmp_cset, &preloaded, mg_preload_node) {
+		cset->mg_src_cgrp = NULL;
+		cset->mg_dst_cgrp = NULL;
+		cset->mg_dst_cset = NULL;
+		list_del_init(&cset->mg_preload_node);
+		put_css_set_locked(cset);
+	}
+
+	spin_unlock_irq(&css_set_lock);
+}
+
+/**
+ * cgroup_migrate_add_src - add a migration source css_set
+ * @src_cset: the source css_set to add
+ * @dst_cgrp: the destination cgroup
+ * @mgctx: migration context
+ *
+ * Tasks belonging to @src_cset are about to be migrated to @dst_cgrp.  Pin
+ * @src_cset and add it to @mgctx->src_csets, which should later be cleaned
+ * up by cgroup_migrate_finish().
+ *
+ * This function may be called without holding cgroup_threadgroup_rwsem
+ * even if the target is a process.  Threads may be created and destroyed
+ * but as long as cgroup_mutex is not dropped, no new css_set can be put
+ * into play and the preloaded css_sets are guaranteed to cover all
+ * migrations.
+ */
+void cgroup_migrate_add_src(struct css_set *src_cset,
+			    struct cgroup *dst_cgrp,
+			    struct cgroup_mgctx *mgctx)
+{
+	struct cgroup *src_cgrp;
+
+	lockdep_assert_held(&cgroup_mutex);
+	lockdep_assert_held(&css_set_lock);
+
+	/*
+	 * If ->dead, @src_set is associated with one or more dead cgroups
+	 * and doesn't contain any migratable tasks.  Ignore it early so
+	 * that the rest of migration path doesn't get confused by it.
+	 */
+	if (src_cset->dead)
+		return;
+
+	src_cgrp = cset_cgroup_from_root(src_cset, dst_cgrp->root);
+
+	if (!list_empty(&src_cset->mg_preload_node))
+		return;
+
+	WARN_ON(src_cset->mg_src_cgrp);
+	WARN_ON(src_cset->mg_dst_cgrp);
+	WARN_ON(!list_empty(&src_cset->mg_tasks));
+	WARN_ON(!list_empty(&src_cset->mg_node));
+
+	src_cset->mg_src_cgrp = src_cgrp;
+	src_cset->mg_dst_cgrp = dst_cgrp;
+	get_css_set(src_cset);
+	list_add_tail(&src_cset->mg_preload_node, &mgctx->preloaded_src_csets);
+}
+
+/**
+ * cgroup_migrate_prepare_dst - prepare destination css_sets for migration
+ * @mgctx: migration context
+ *
+ * Tasks are about to be moved and all the source css_sets have been
+ * preloaded to @mgctx->preloaded_src_csets.  This function looks up and
+ * pins all destination css_sets, links each to its source, and append them
+ * to @mgctx->preloaded_dst_csets.
+ *
+ * This function must be called after cgroup_migrate_add_src() has been
+ * called on each migration source css_set.  After migration is performed
+ * using cgroup_migrate(), cgroup_migrate_finish() must be called on
+ * @mgctx.
+ */
+int cgroup_migrate_prepare_dst(struct cgroup_mgctx *mgctx)
+{
+	struct css_set *src_cset, *tmp_cset;
+
+	lockdep_assert_held(&cgroup_mutex);
+
+	/* look up the dst cset for each src cset and link it to src */
+	list_for_each_entry_safe(src_cset, tmp_cset, &mgctx->preloaded_src_csets,
+				 mg_preload_node) {
+		struct css_set *dst_cset;
+		struct cgroup_subsys *ss;
+		int ssid;
+
+		dst_cset = find_css_set(src_cset, src_cset->mg_dst_cgrp);
+		if (!dst_cset)
+			goto err;
+
+		WARN_ON_ONCE(src_cset->mg_dst_cset || dst_cset->mg_dst_cset);
+
+		/*
+		 * If src cset equals dst, it's noop.  Drop the src.
+		 * cgroup_migrate() will skip the cset too.  Note that we
+		 * can't handle src == dst as some nodes are used by both.
+		 */
+		if (src_cset == dst_cset) {
+			src_cset->mg_src_cgrp = NULL;
+			src_cset->mg_dst_cgrp = NULL;
+			list_del_init(&src_cset->mg_preload_node);
+			put_css_set(src_cset);
+			put_css_set(dst_cset);
+			continue;
+		}
+
+		src_cset->mg_dst_cset = dst_cset;
+
+		if (list_empty(&dst_cset->mg_preload_node))
+			list_add_tail(&dst_cset->mg_preload_node,
+				      &mgctx->preloaded_dst_csets);
+		else
+			put_css_set(dst_cset);
+
+		for_each_subsys(ss, ssid)
+			if (src_cset->subsys[ssid] != dst_cset->subsys[ssid])
+				mgctx->ss_mask |= 1 << ssid;
+	}
+
+	return 0;
+err:
+	cgroup_migrate_finish(mgctx);
+	return -ENOMEM;
+}
+
+/**
+ * cgroup_migrate - migrate a process or task to a cgroup
+ * @leader: the leader of the process or the task to migrate
+ * @threadgroup: whether @leader points to the whole process or a single task
+ * @mgctx: migration context
+ *
+ * Migrate a process or task denoted by @leader.  If migrating a process,
+ * the caller must be holding cgroup_threadgroup_rwsem.  The caller is also
+ * responsible for invoking cgroup_migrate_add_src() and
+ * cgroup_migrate_prepare_dst() on the targets before invoking this
+ * function and following up with cgroup_migrate_finish().
+ *
+ * As long as a controller's ->can_attach() doesn't fail, this function is
+ * guaranteed to succeed.  This means that, excluding ->can_attach()
+ * failure, when migrating multiple targets, the success or failure can be
+ * decided for all targets by invoking group_migrate_prepare_dst() before
+ * actually starting migrating.
+ */
+int cgroup_migrate(struct task_struct *leader, bool threadgroup,
+		   struct cgroup_mgctx *mgctx)
+{
+	struct task_struct *task;
+
+	/*
+	 * Prevent freeing of tasks while we take a snapshot. Tasks that are
+	 * already PF_EXITING could be freed from underneath us unless we
+	 * take an rcu_read_lock.
+	 */
+	spin_lock_irq(&css_set_lock);
+	rcu_read_lock();
+	task = leader;
+	do {
+		cgroup_migrate_add_task(task, mgctx);
+		if (!threadgroup)
+			break;
+	} while_each_thread(leader, task);
+	rcu_read_unlock();
+	spin_unlock_irq(&css_set_lock);
+
+	return cgroup_migrate_execute(mgctx);
+}
+
+/**
+ * cgroup_attach_task - attach a task or a whole threadgroup to a cgroup
+ * @dst_cgrp: the cgroup to attach to
+ * @leader: the task or the leader of the threadgroup to be attached
+ * @threadgroup: attach the whole threadgroup?
+ *
+ * Call holding cgroup_mutex and cgroup_threadgroup_rwsem.
+ */
+int cgroup_attach_task(struct cgroup *dst_cgrp, struct task_struct *leader,
+		       bool threadgroup)
+{
+	DEFINE_CGROUP_MGCTX(mgctx);
+	struct task_struct *task;
+	int ret;
+
+	ret = cgroup_migrate_vet_dst(dst_cgrp);
+	if (ret)
+		return ret;
+
+	/* look up all src csets */
+	spin_lock_irq(&css_set_lock);
+	rcu_read_lock();
+	task = leader;
+	do {
+		cgroup_migrate_add_src(task_css_set(task), dst_cgrp, &mgctx);
+		if (!threadgroup)
+			break;
+	} while_each_thread(leader, task);
+	rcu_read_unlock();
+	spin_unlock_irq(&css_set_lock);
+
+	/* prepare dst csets and commit */
+	ret = cgroup_migrate_prepare_dst(&mgctx);
+	if (!ret)
+		ret = cgroup_migrate(leader, threadgroup, &mgctx);
+
+	cgroup_migrate_finish(&mgctx);
+
+	if (!ret)
+		TRACE_CGROUP_PATH(attach_task, dst_cgrp, leader, threadgroup);
+
+	return ret;
+}
+
+struct task_struct *cgroup_procs_write_start(char *buf, bool threadgroup)
+	__acquires(&cgroup_threadgroup_rwsem)
+{
+	struct task_struct *tsk;
+	pid_t pid;
+
+	if (kstrtoint(strstrip(buf), 0, &pid) || pid < 0)
+		return ERR_PTR(-EINVAL);
+
+	percpu_down_write(&cgroup_threadgroup_rwsem);
+
+	rcu_read_lock();
+	if (pid) {
+		tsk = find_task_by_vpid(pid);
+		if (!tsk) {
+			tsk = ERR_PTR(-ESRCH);
+			goto out_unlock_threadgroup;
+		}
+	} else {
+		tsk = current;
+	}
+
+	if (threadgroup)
+		tsk = tsk->group_leader;
+
+	/*
+	 * kthreads may acquire PF_NO_SETAFFINITY during initialization.
+	 * If userland migrates such a kthread to a non-root cgroup, it can
+	 * become trapped in a cpuset, or RT kthread may be born in a
+	 * cgroup with no rt_runtime allocated.  Just say no.
+	 */
+	if (tsk->no_cgroup_migration || (tsk->flags & PF_NO_SETAFFINITY)) {
+		tsk = ERR_PTR(-EINVAL);
+		goto out_unlock_threadgroup;
+	}
+
+	get_task_struct(tsk);
+	goto out_unlock_rcu;
+
+out_unlock_threadgroup:
+	percpu_up_write(&cgroup_threadgroup_rwsem);
+out_unlock_rcu:
+	rcu_read_unlock();
+	return tsk;
+}
+
+void cgroup_procs_write_finish(struct task_struct *task)
+	__releases(&cgroup_threadgroup_rwsem)
+{
+	struct cgroup_subsys *ss;
+	int ssid;
+
+	/* release reference from cgroup_procs_write_start() */
+	put_task_struct(task);
+
+	percpu_up_write(&cgroup_threadgroup_rwsem);
+	for_each_subsys(ss, ssid)
+		if (ss->post_attach)
+			ss->post_attach();
+}
+
+static void cgroup_print_ss_mask(struct seq_file *seq, u16 ss_mask)
+{
+	struct cgroup_subsys *ss;
+	bool printed = false;
+	int ssid;
+
+	do_each_subsys_mask(ss, ssid, ss_mask) {
+		if (printed)
+			seq_putc(seq, ' ');
+		seq_printf(seq, "%s", ss->name);
+		printed = true;
+	} while_each_subsys_mask();
+	if (printed)
+		seq_putc(seq, '\n');
+}
+
+/* show controllers which are enabled from the parent */
+static int cgroup_controllers_show(struct seq_file *seq, void *v)
+{
+	struct cgroup *cgrp = seq_css(seq)->cgroup;
+
+	cgroup_print_ss_mask(seq, cgroup_control(cgrp));
+	return 0;
+}
+
+/* show controllers which are enabled for a given cgroup's children */
+static int cgroup_subtree_control_show(struct seq_file *seq, void *v)
+{
+	struct cgroup *cgrp = seq_css(seq)->cgroup;
+
+	cgroup_print_ss_mask(seq, cgrp->subtree_control);
+	return 0;
+}
+
+/**
+ * cgroup_update_dfl_csses - update css assoc of a subtree in default hierarchy
+ * @cgrp: root of the subtree to update csses for
+ *
+ * @cgrp's control masks have changed and its subtree's css associations
+ * need to be updated accordingly.  This function looks up all css_sets
+ * which are attached to the subtree, creates the matching updated css_sets
+ * and migrates the tasks to the new ones.
+ */
+static int cgroup_update_dfl_csses(struct cgroup *cgrp)
+{
+	DEFINE_CGROUP_MGCTX(mgctx);
+	struct cgroup_subsys_state *d_css;
+	struct cgroup *dsct;
+	struct css_set *src_cset;
+	int ret;
+
+	lockdep_assert_held(&cgroup_mutex);
+
+	percpu_down_write(&cgroup_threadgroup_rwsem);
+
+	/* look up all csses currently attached to @cgrp's subtree */
+	spin_lock_irq(&css_set_lock);
+	cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp) {
+		struct cgrp_cset_link *link;
+
+		list_for_each_entry(link, &dsct->cset_links, cset_link)
+			cgroup_migrate_add_src(link->cset, dsct, &mgctx);
+	}
+	spin_unlock_irq(&css_set_lock);
+
+	/* NULL dst indicates self on default hierarchy */
+	ret = cgroup_migrate_prepare_dst(&mgctx);
+	if (ret)
+		goto out_finish;
+
+	spin_lock_irq(&css_set_lock);
+	list_for_each_entry(src_cset, &mgctx.preloaded_src_csets, mg_preload_node) {
+		struct task_struct *task, *ntask;
+
+		/* all tasks in src_csets need to be migrated */
+		list_for_each_entry_safe(task, ntask, &src_cset->tasks, cg_list)
+			cgroup_migrate_add_task(task, &mgctx);
+	}
+	spin_unlock_irq(&css_set_lock);
+
+	ret = cgroup_migrate_execute(&mgctx);
+out_finish:
+	cgroup_migrate_finish(&mgctx);
+	percpu_up_write(&cgroup_threadgroup_rwsem);
+	return ret;
+}
+
+/**
+ * cgroup_lock_and_drain_offline - lock cgroup_mutex and drain offlined csses
+ * @cgrp: root of the target subtree
+ *
+ * Because css offlining is asynchronous, userland may try to re-enable a
+ * controller while the previous css is still around.  This function grabs
+ * cgroup_mutex and drains the previous css instances of @cgrp's subtree.
+ */
+void cgroup_lock_and_drain_offline(struct cgroup *cgrp)
+	__acquires(&cgroup_mutex)
+{
+	struct cgroup *dsct;
+	struct cgroup_subsys_state *d_css;
+	struct cgroup_subsys *ss;
+	int ssid;
+
+restart:
+	mutex_lock(&cgroup_mutex);
+
+	cgroup_for_each_live_descendant_post(dsct, d_css, cgrp) {
+		for_each_subsys(ss, ssid) {
+			struct cgroup_subsys_state *css = cgroup_css(dsct, ss);
+			DEFINE_WAIT(wait);
+
+			if (!css || !percpu_ref_is_dying(&css->refcnt))
+				continue;
+
+			cgroup_get_live(dsct);
+			prepare_to_wait(&dsct->offline_waitq, &wait,
+					TASK_UNINTERRUPTIBLE);
+
+			mutex_unlock(&cgroup_mutex);
+			schedule();
+			finish_wait(&dsct->offline_waitq, &wait);
+
+			cgroup_put(dsct);
+			goto restart;
+		}
+	}
+}
+
+/**
+ * cgroup_save_control - save control masks and dom_cgrp of a subtree
+ * @cgrp: root of the target subtree
+ *
+ * Save ->subtree_control, ->subtree_ss_mask and ->dom_cgrp to the
+ * respective old_ prefixed fields for @cgrp's subtree including @cgrp
+ * itself.
+ */
+static void cgroup_save_control(struct cgroup *cgrp)
+{
+	struct cgroup *dsct;
+	struct cgroup_subsys_state *d_css;
+
+	cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp) {
+		dsct->old_subtree_control = dsct->subtree_control;
+		dsct->old_subtree_ss_mask = dsct->subtree_ss_mask;
+		dsct->old_dom_cgrp = dsct->dom_cgrp;
+	}
+}
+
+/**
+ * cgroup_propagate_control - refresh control masks of a subtree
+ * @cgrp: root of the target subtree
+ *
+ * For @cgrp and its subtree, ensure ->subtree_ss_mask matches
+ * ->subtree_control and propagate controller availability through the
+ * subtree so that descendants don't have unavailable controllers enabled.
+ */
+static void cgroup_propagate_control(struct cgroup *cgrp)
+{
+	struct cgroup *dsct;
+	struct cgroup_subsys_state *d_css;
+
+	cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp) {
+		dsct->subtree_control &= cgroup_control(dsct);
+		dsct->subtree_ss_mask =
+			cgroup_calc_subtree_ss_mask(dsct->subtree_control,
+						    cgroup_ss_mask(dsct));
+	}
+}
+
+/**
+ * cgroup_restore_control - restore control masks and dom_cgrp of a subtree
+ * @cgrp: root of the target subtree
+ *
+ * Restore ->subtree_control, ->subtree_ss_mask and ->dom_cgrp from the
+ * respective old_ prefixed fields for @cgrp's subtree including @cgrp
+ * itself.
+ */
+static void cgroup_restore_control(struct cgroup *cgrp)
+{
+	struct cgroup *dsct;
+	struct cgroup_subsys_state *d_css;
+
+	cgroup_for_each_live_descendant_post(dsct, d_css, cgrp) {
+		dsct->subtree_control = dsct->old_subtree_control;
+		dsct->subtree_ss_mask = dsct->old_subtree_ss_mask;
+		dsct->dom_cgrp = dsct->old_dom_cgrp;
+	}
+}
+
+static bool css_visible(struct cgroup_subsys_state *css)
+{
+	struct cgroup_subsys *ss = css->ss;
+	struct cgroup *cgrp = css->cgroup;
+
+	if (cgroup_control(cgrp) & (1 << ss->id))
+		return true;
+	if (!(cgroup_ss_mask(cgrp) & (1 << ss->id)))
+		return false;
+	return cgroup_on_dfl(cgrp) && ss->implicit_on_dfl;
+}
+
+/**
+ * cgroup_apply_control_enable - enable or show csses according to control
+ * @cgrp: root of the target subtree
+ *
+ * Walk @cgrp's subtree and create new csses or make the existing ones
+ * visible.  A css is created invisible if it's being implicitly enabled
+ * through dependency.  An invisible css is made visible when the userland
+ * explicitly enables it.
+ *
+ * Returns 0 on success, -errno on failure.  On failure, csses which have
+ * been processed already aren't cleaned up.  The caller is responsible for
+ * cleaning up with cgroup_apply_control_disable().
+ */
+static int cgroup_apply_control_enable(struct cgroup *cgrp)
+{
+	struct cgroup *dsct;
+	struct cgroup_subsys_state *d_css;
+	struct cgroup_subsys *ss;
+	int ssid, ret;
+
+	cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp) {
+		for_each_subsys(ss, ssid) {
+			struct cgroup_subsys_state *css = cgroup_css(dsct, ss);
+
+			if (!(cgroup_ss_mask(dsct) & (1 << ss->id)))
+				continue;
+
+			if (!css) {
+				css = css_create(dsct, ss);
+				if (IS_ERR(css))
+					return PTR_ERR(css);
+			}
+
+			WARN_ON_ONCE(percpu_ref_is_dying(&css->refcnt));
+
+			if (css_visible(css)) {
+				ret = css_populate_dir(css);
+				if (ret)
+					return ret;
+			}
+		}
+	}
+
+	return 0;
+}
+
+/**
+ * cgroup_apply_control_disable - kill or hide csses according to control
+ * @cgrp: root of the target subtree
+ *
+ * Walk @cgrp's subtree and kill and hide csses so that they match
+ * cgroup_ss_mask() and cgroup_visible_mask().
+ *
+ * A css is hidden when the userland requests it to be disabled while other
+ * subsystems are still depending on it.  The css must not actively control
+ * resources and be in the vanilla state if it's made visible again later.
+ * Controllers which may be depended upon should provide ->css_reset() for
+ * this purpose.
+ */
+static void cgroup_apply_control_disable(struct cgroup *cgrp)
+{
+	struct cgroup *dsct;
+	struct cgroup_subsys_state *d_css;
+	struct cgroup_subsys *ss;
+	int ssid;
+
+	cgroup_for_each_live_descendant_post(dsct, d_css, cgrp) {
+		for_each_subsys(ss, ssid) {
+			struct cgroup_subsys_state *css = cgroup_css(dsct, ss);
+
+			if (!css)
+				continue;
+
+			WARN_ON_ONCE(percpu_ref_is_dying(&css->refcnt));
+
+			if (css->parent &&
+			    !(cgroup_ss_mask(dsct) & (1 << ss->id))) {
+				kill_css(css);
+			} else if (!css_visible(css)) {
+				css_clear_dir(css);
+				if (ss->css_reset)
+					ss->css_reset(css);
+			}
+		}
+	}
+}
+
+/**
+ * cgroup_apply_control - apply control mask updates to the subtree
+ * @cgrp: root of the target subtree
+ *
+ * subsystems can be enabled and disabled in a subtree using the following
+ * steps.
+ *
+ * 1. Call cgroup_save_control() to stash the current state.
+ * 2. Update ->subtree_control masks in the subtree as desired.
+ * 3. Call cgroup_apply_control() to apply the changes.
+ * 4. Optionally perform other related operations.
+ * 5. Call cgroup_finalize_control() to finish up.
+ *
+ * This function implements step 3 and propagates the mask changes
+ * throughout @cgrp's subtree, updates csses accordingly and perform
+ * process migrations.
+ */
+static int cgroup_apply_control(struct cgroup *cgrp)
+{
+	int ret;
+
+	cgroup_propagate_control(cgrp);
+
+	ret = cgroup_apply_control_enable(cgrp);
+	if (ret)
+		return ret;
+
+	/*
+	 * At this point, cgroup_e_css() results reflect the new csses
+	 * making the following cgroup_update_dfl_csses() properly update
+	 * css associations of all tasks in the subtree.
+	 */
+	ret = cgroup_update_dfl_csses(cgrp);
+	if (ret)
+		return ret;
+
+	return 0;
+}
+
+/**
+ * cgroup_finalize_control - finalize control mask update
+ * @cgrp: root of the target subtree
+ * @ret: the result of the update
+ *
+ * Finalize control mask update.  See cgroup_apply_control() for more info.
+ */
+static void cgroup_finalize_control(struct cgroup *cgrp, int ret)
+{
+	if (ret) {
+		cgroup_restore_control(cgrp);
+		cgroup_propagate_control(cgrp);
+	}
+
+	cgroup_apply_control_disable(cgrp);
+}
+
+static int cgroup_vet_subtree_control_enable(struct cgroup *cgrp, u16 enable)
+{
+	u16 domain_enable = enable & ~cgrp_dfl_threaded_ss_mask;
+
+	/* if nothing is getting enabled, nothing to worry about */
+	if (!enable)
+		return 0;
+
+	/* can @cgrp host any resources? */
+	if (!cgroup_is_valid_domain(cgrp->dom_cgrp))
+		return -EOPNOTSUPP;
+
+	/* mixables don't care */
+	if (cgroup_is_mixable(cgrp))
+		return 0;
+
+	if (domain_enable) {
+		/* can't enable domain controllers inside a thread subtree */
+		if (cgroup_is_thread_root(cgrp) || cgroup_is_threaded(cgrp))
+			return -EOPNOTSUPP;
+	} else {
+		/*
+		 * Threaded controllers can handle internal competitions
+		 * and are always allowed inside a (prospective) thread
+		 * subtree.
+		 */
+		if (cgroup_can_be_thread_root(cgrp) || cgroup_is_threaded(cgrp))
+			return 0;
+	}
+
+	/*
+	 * Controllers can't be enabled for a cgroup with tasks to avoid
+	 * child cgroups competing against tasks.
+	 */
+	if (cgroup_has_tasks(cgrp))
+		return -EBUSY;
+
+	return 0;
+}
+
+/* change the enabled child controllers for a cgroup in the default hierarchy */
+static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,
+					    char *buf, size_t nbytes,
+					    loff_t off)
+{
+	u16 enable = 0, disable = 0;
+	struct cgroup *cgrp, *child;
+	struct cgroup_subsys *ss;
+	char *tok;
+	int ssid, ret;
+
+	/*
+	 * Parse input - space separated list of subsystem names prefixed
+	 * with either + or -.
+	 */
+	buf = strstrip(buf);
+	while ((tok = strsep(&buf, " "))) {
+		if (tok[0] == '\0')
+			continue;
+		do_each_subsys_mask(ss, ssid, ~cgrp_dfl_inhibit_ss_mask) {
+			if (!cgroup_ssid_enabled(ssid) ||
+			    strcmp(tok + 1, ss->name))
+				continue;
+
+			if (*tok == '+') {
+				enable |= 1 << ssid;
+				disable &= ~(1 << ssid);
+			} else if (*tok == '-') {
+				disable |= 1 << ssid;
+				enable &= ~(1 << ssid);
+			} else {
+				return -EINVAL;
+			}
+			break;
+		} while_each_subsys_mask();
+		if (ssid == CGROUP_SUBSYS_COUNT)
+			return -EINVAL;
+	}
+
+	cgrp = cgroup_kn_lock_live(of->kn, true);
+	if (!cgrp)
+		return -ENODEV;
+
+	for_each_subsys(ss, ssid) {
+		if (enable & (1 << ssid)) {
+			if (cgrp->subtree_control & (1 << ssid)) {
+				enable &= ~(1 << ssid);
+				continue;
+			}
+
+			if (!(cgroup_control(cgrp) & (1 << ssid))) {
+				ret = -ENOENT;
+				goto out_unlock;
+			}
+		} else if (disable & (1 << ssid)) {
+			if (!(cgrp->subtree_control & (1 << ssid))) {
+				disable &= ~(1 << ssid);
+				continue;
+			}
+
+			/* a child has it enabled? */
+			cgroup_for_each_live_child(child, cgrp) {
+				if (child->subtree_control & (1 << ssid)) {
+					ret = -EBUSY;
+					goto out_unlock;
+				}
+			}
+		}
+	}
+
+	if (!enable && !disable) {
+		ret = 0;
+		goto out_unlock;
+	}
+
+	ret = cgroup_vet_subtree_control_enable(cgrp, enable);
+	if (ret)
+		goto out_unlock;
+
+	/* save and update control masks and prepare csses */
+	cgroup_save_control(cgrp);
+
+	cgrp->subtree_control |= enable;
+	cgrp->subtree_control &= ~disable;
+
+	ret = cgroup_apply_control(cgrp);
+	cgroup_finalize_control(cgrp, ret);
+	if (ret)
+		goto out_unlock;
+
+	kernfs_activate(cgrp->kn);
+out_unlock:
+	cgroup_kn_unlock(of->kn);
+	return ret ?: nbytes;
+}
+
+/**
+ * cgroup_enable_threaded - make @cgrp threaded
+ * @cgrp: the target cgroup
+ *
+ * Called when "threaded" is written to the cgroup.type interface file and
+ * tries to make @cgrp threaded and join the parent's resource domain.
+ * This function is never called on the root cgroup as cgroup.type doesn't
+ * exist on it.
+ */
+static int cgroup_enable_threaded(struct cgroup *cgrp)
+{
+	struct cgroup *parent = cgroup_parent(cgrp);
+	struct cgroup *dom_cgrp = parent->dom_cgrp;
+	struct cgroup *dsct;
+	struct cgroup_subsys_state *d_css;
+	int ret;
+
+	lockdep_assert_held(&cgroup_mutex);
+
+	/* noop if already threaded */
+	if (cgroup_is_threaded(cgrp))
+		return 0;
+
+	/*
+	 * If @cgroup is populated or has domain controllers enabled, it
+	 * can't be switched.  While the below cgroup_can_be_thread_root()
+	 * test can catch the same conditions, that's only when @parent is
+	 * not mixable, so let's check it explicitly.
+	 */
+	if (cgroup_is_populated(cgrp) ||
+	    cgrp->subtree_control & ~cgrp_dfl_threaded_ss_mask)
+		return -EOPNOTSUPP;
+
+	/* we're joining the parent's domain, ensure its validity */
+	if (!cgroup_is_valid_domain(dom_cgrp) ||
+	    !cgroup_can_be_thread_root(dom_cgrp))
+		return -EOPNOTSUPP;
+
+	/*
+	 * The following shouldn't cause actual migrations and should
+	 * always succeed.
+	 */
+	cgroup_save_control(cgrp);
+
+	cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp)
+		if (dsct == cgrp || cgroup_is_threaded(dsct))
+			dsct->dom_cgrp = dom_cgrp;
+
+	ret = cgroup_apply_control(cgrp);
+	if (!ret)
+		parent->nr_threaded_children++;
+
+	cgroup_finalize_control(cgrp, ret);
+	return ret;
+}
+
+static int cgroup_type_show(struct seq_file *seq, void *v)
+{
+	struct cgroup *cgrp = seq_css(seq)->cgroup;
+
+	if (cgroup_is_threaded(cgrp))
+		seq_puts(seq, "threaded\n");
+	else if (!cgroup_is_valid_domain(cgrp))
+		seq_puts(seq, "domain invalid\n");
+	else if (cgroup_is_thread_root(cgrp))
+		seq_puts(seq, "domain threaded\n");
+	else
+		seq_puts(seq, "domain\n");
+
+	return 0;
+}
+
+static ssize_t cgroup_type_write(struct kernfs_open_file *of, char *buf,
+				 size_t nbytes, loff_t off)
+{
+	struct cgroup *cgrp;
+	int ret;
+
+	/* only switching to threaded mode is supported */
+	if (strcmp(strstrip(buf), "threaded"))
+		return -EINVAL;
+
+	/* drain dying csses before we re-apply (threaded) subtree control */
+	cgrp = cgroup_kn_lock_live(of->kn, true);
+	if (!cgrp)
+		return -ENOENT;
+
+	/* threaded can only be enabled */
+	ret = cgroup_enable_threaded(cgrp);
+
+	cgroup_kn_unlock(of->kn);
+	return ret ?: nbytes;
+}
+
+static int cgroup_max_descendants_show(struct seq_file *seq, void *v)
+{
+	struct cgroup *cgrp = seq_css(seq)->cgroup;
+	int descendants = READ_ONCE(cgrp->max_descendants);
+
+	if (descendants == INT_MAX)
+		seq_puts(seq, "max\n");
+	else
+		seq_printf(seq, "%d\n", descendants);
+
+	return 0;
+}
+
+static ssize_t cgroup_max_descendants_write(struct kernfs_open_file *of,
+					   char *buf, size_t nbytes, loff_t off)
+{
+	struct cgroup *cgrp;
+	int descendants;
+	ssize_t ret;
+
+	buf = strstrip(buf);
+	if (!strcmp(buf, "max")) {
+		descendants = INT_MAX;
+	} else {
+		ret = kstrtoint(buf, 0, &descendants);
+		if (ret)
+			return ret;
+	}
+
+	if (descendants < 0)
+		return -ERANGE;
+
+	cgrp = cgroup_kn_lock_live(of->kn, false);
+	if (!cgrp)
+		return -ENOENT;
+
+	cgrp->max_descendants = descendants;
+
+	cgroup_kn_unlock(of->kn);
+
+	return nbytes;
+}
+
+static int cgroup_max_depth_show(struct seq_file *seq, void *v)
+{
+	struct cgroup *cgrp = seq_css(seq)->cgroup;
+	int depth = READ_ONCE(cgrp->max_depth);
+
+	if (depth == INT_MAX)
+		seq_puts(seq, "max\n");
+	else
+		seq_printf(seq, "%d\n", depth);
+
+	return 0;
+}
+
+static ssize_t cgroup_max_depth_write(struct kernfs_open_file *of,
+				      char *buf, size_t nbytes, loff_t off)
+{
+	struct cgroup *cgrp;
+	ssize_t ret;
+	int depth;
+
+	buf = strstrip(buf);
+	if (!strcmp(buf, "max")) {
+		depth = INT_MAX;
+	} else {
+		ret = kstrtoint(buf, 0, &depth);
+		if (ret)
+			return ret;
+	}
+
+	if (depth < 0)
+		return -ERANGE;
+
+	cgrp = cgroup_kn_lock_live(of->kn, false);
+	if (!cgrp)
+		return -ENOENT;
+
+	cgrp->max_depth = depth;
+
+	cgroup_kn_unlock(of->kn);
+
+	return nbytes;
+}
+
+static int cgroup_events_show(struct seq_file *seq, void *v)
+{
+	seq_printf(seq, "populated %d\n",
+		   cgroup_is_populated(seq_css(seq)->cgroup));
+	return 0;
+}
+
+static int cgroup_stat_show(struct seq_file *seq, void *v)
+{
+	struct cgroup *cgroup = seq_css(seq)->cgroup;
+
+	seq_printf(seq, "nr_descendants %d\n",
+		   cgroup->nr_descendants);
+	seq_printf(seq, "nr_dying_descendants %d\n",
+		   cgroup->nr_dying_descendants);
+
+	return 0;
+}
+
+static int __maybe_unused cgroup_extra_stat_show(struct seq_file *seq,
+						 struct cgroup *cgrp, int ssid)
+{
+	struct cgroup_subsys *ss = cgroup_subsys[ssid];
+	struct cgroup_subsys_state *css;
+	int ret;
+
+	if (!ss->css_extra_stat_show)
+		return 0;
+
+	css = cgroup_tryget_css(cgrp, ss);
+	if (!css)
+		return 0;
+
+	ret = ss->css_extra_stat_show(seq, css);
+	css_put(css);
+	return ret;
+}
+
+static int cpu_stat_show(struct seq_file *seq, void *v)
+{
+	struct cgroup __maybe_unused *cgrp = seq_css(seq)->cgroup;
+	int ret = 0;
+
+	cgroup_base_stat_cputime_show(seq);
+#ifdef CONFIG_CGROUP_SCHED
+	ret = cgroup_extra_stat_show(seq, cgrp, cpu_cgrp_id);
+#endif
+	return ret;
+}
+
+static int cgroup_file_open(struct kernfs_open_file *of)
+{
+	struct cftype *cft = of->kn->priv;
+	struct cgroup_file_ctx *ctx;
+	int ret;
+
+	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
+	if (!ctx)
+		return -ENOMEM;
+
+	ctx->ns = current->nsproxy->cgroup_ns;
+	get_cgroup_ns(ctx->ns);
+	of->priv = ctx;
+
+	if (!cft->open)
+		return 0;
+
+	ret = cft->open(of);
+	if (ret) {
+		put_cgroup_ns(ctx->ns);
+		kfree(ctx);
+	}
+	return ret;
+}
+
+static void cgroup_file_release(struct kernfs_open_file *of)
+{
+	struct cftype *cft = of->kn->priv;
+	struct cgroup_file_ctx *ctx = of->priv;
+
+	if (cft->release)
+		cft->release(of);
+	put_cgroup_ns(ctx->ns);
+	kfree(ctx);
+}
+
+static ssize_t cgroup_file_write(struct kernfs_open_file *of, char *buf,
+				 size_t nbytes, loff_t off)
+{
+	struct cgroup_file_ctx *ctx = of->priv;
+	struct cgroup *cgrp = of->kn->parent->priv;
+	struct cftype *cft = of->kn->priv;
+	struct cgroup_subsys_state *css;
+	int ret;
+
+	/*
+	 * If namespaces are delegation boundaries, disallow writes to
+	 * files in an non-init namespace root from inside the namespace
+	 * except for the files explicitly marked delegatable -
+	 * cgroup.procs and cgroup.subtree_control.
+	 */
+	if ((cgrp->root->flags & CGRP_ROOT_NS_DELEGATE) &&
+	    !(cft->flags & CFTYPE_NS_DELEGATABLE) &&
+	    ctx->ns != &init_cgroup_ns && ctx->ns->root_cset->dfl_cgrp == cgrp)
+		return -EPERM;
+
+	if (cft->write)
+		return cft->write(of, buf, nbytes, off);
+
+	/*
+	 * kernfs guarantees that a file isn't deleted with operations in
+	 * flight, which means that the matching css is and stays alive and
+	 * doesn't need to be pinned.  The RCU locking is not necessary
+	 * either.  It's just for the convenience of using cgroup_css().
+	 */
+	rcu_read_lock();
+	css = cgroup_css(cgrp, cft->ss);
+	rcu_read_unlock();
+
+	if (cft->write_u64) {
+		unsigned long long v;
+		ret = kstrtoull(buf, 0, &v);
+		if (!ret)
+			ret = cft->write_u64(css, cft, v);
+	} else if (cft->write_s64) {
+		long long v;
+		ret = kstrtoll(buf, 0, &v);
+		if (!ret)
+			ret = cft->write_s64(css, cft, v);
+	} else {
+		ret = -EINVAL;
+	}
+
+	return ret ?: nbytes;
+}
+
+static void *cgroup_seqfile_start(struct seq_file *seq, loff_t *ppos)
+{
+	return seq_cft(seq)->seq_start(seq, ppos);
+}
+
+static void *cgroup_seqfile_next(struct seq_file *seq, void *v, loff_t *ppos)
+{
+	return seq_cft(seq)->seq_next(seq, v, ppos);
+}
+
+static void cgroup_seqfile_stop(struct seq_file *seq, void *v)
+{
+	if (seq_cft(seq)->seq_stop)
+		seq_cft(seq)->seq_stop(seq, v);
+}
+
+static int cgroup_seqfile_show(struct seq_file *m, void *arg)
+{
+	struct cftype *cft = seq_cft(m);
+	struct cgroup_subsys_state *css = seq_css(m);
+
+	if (cft->seq_show)
+		return cft->seq_show(m, arg);
+
+	if (cft->read_u64)
+		seq_printf(m, "%llu\n", cft->read_u64(css, cft));
+	else if (cft->read_s64)
+		seq_printf(m, "%lld\n", cft->read_s64(css, cft));
+	else
+		return -EINVAL;
+	return 0;
+}
+
+static struct kernfs_ops cgroup_kf_single_ops = {
+	.atomic_write_len	= PAGE_SIZE,
+	.open			= cgroup_file_open,
+	.release		= cgroup_file_release,
+	.write			= cgroup_file_write,
+	.seq_show		= cgroup_seqfile_show,
+};
+
+static struct kernfs_ops cgroup_kf_ops = {
+	.atomic_write_len	= PAGE_SIZE,
+	.open			= cgroup_file_open,
+	.release		= cgroup_file_release,
+	.write			= cgroup_file_write,
+	.seq_start		= cgroup_seqfile_start,
+	.seq_next		= cgroup_seqfile_next,
+	.seq_stop		= cgroup_seqfile_stop,
+	.seq_show		= cgroup_seqfile_show,
+};
+
+/* set uid and gid of cgroup dirs and files to that of the creator */
+static int cgroup_kn_set_ugid(struct kernfs_node *kn)
+{
+	struct iattr iattr = { .ia_valid = ATTR_UID | ATTR_GID,
+			       .ia_uid = current_fsuid(),
+			       .ia_gid = current_fsgid(), };
+
+	if (uid_eq(iattr.ia_uid, GLOBAL_ROOT_UID) &&
+	    gid_eq(iattr.ia_gid, GLOBAL_ROOT_GID))
+		return 0;
+
+	return kernfs_setattr(kn, &iattr);
+}
+
+static void cgroup_file_notify_timer(struct timer_list *timer)
+{
+	cgroup_file_notify(container_of(timer, struct cgroup_file,
+					notify_timer));
+}
+
+static int cgroup_add_file(struct cgroup_subsys_state *css, struct cgroup *cgrp,
+			   struct cftype *cft)
+{
+	char name[CGROUP_FILE_NAME_MAX];
+	struct kernfs_node *kn;
+	struct lock_class_key *key = NULL;
+	int ret;
+
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+	key = &cft->lockdep_key;
+#endif
+	kn = __kernfs_create_file(cgrp->kn, cgroup_file_name(cgrp, cft, name),
+				  cgroup_file_mode(cft),
+				  GLOBAL_ROOT_UID, GLOBAL_ROOT_GID,
+				  0, cft->kf_ops, cft,
+				  NULL, key);
+	if (IS_ERR(kn))
+		return PTR_ERR(kn);
+
+	ret = cgroup_kn_set_ugid(kn);
+	if (ret) {
+		kernfs_remove(kn);
+		return ret;
+	}
+
+	if (cft->file_offset) {
+		struct cgroup_file *cfile = (void *)css + cft->file_offset;
+
+		timer_setup(&cfile->notify_timer, cgroup_file_notify_timer, 0);
+
+		spin_lock_irq(&cgroup_file_kn_lock);
+		cfile->kn = kn;
+		spin_unlock_irq(&cgroup_file_kn_lock);
+	}
+
+	return 0;
+}
+
+/**
+ * cgroup_addrm_files - add or remove files to a cgroup directory
+ * @css: the target css
+ * @cgrp: the target cgroup (usually css->cgroup)
+ * @cfts: array of cftypes to be added
+ * @is_add: whether to add or remove
+ *
+ * Depending on @is_add, add or remove files defined by @cfts on @cgrp.
+ * For removals, this function never fails.
+ */
+static int cgroup_addrm_files(struct cgroup_subsys_state *css,
+			      struct cgroup *cgrp, struct cftype cfts[],
+			      bool is_add)
+{
+	struct cftype *cft, *cft_end = NULL;
+	int ret = 0;
+
+	lockdep_assert_held(&cgroup_mutex);
+
+restart:
+	for (cft = cfts; cft != cft_end && cft->name[0] != '\0'; cft++) {
+		/* does cft->flags tell us to skip this file on @cgrp? */
+		if ((cft->flags & __CFTYPE_ONLY_ON_DFL) && !cgroup_on_dfl(cgrp))
+			continue;
+		if ((cft->flags & __CFTYPE_NOT_ON_DFL) && cgroup_on_dfl(cgrp))
+			continue;
+		if ((cft->flags & CFTYPE_NOT_ON_ROOT) && !cgroup_parent(cgrp))
+			continue;
+		if ((cft->flags & CFTYPE_ONLY_ON_ROOT) && cgroup_parent(cgrp))
+			continue;
+
+		if (is_add) {
+			ret = cgroup_add_file(css, cgrp, cft);
+			if (ret) {
+				pr_warn("%s: failed to add %s, err=%d\n",
+					__func__, cft->name, ret);
+				cft_end = cft;
+				is_add = false;
+				goto restart;
+			}
+		} else {
+			cgroup_rm_file(cgrp, cft);
+		}
+	}
+	return ret;
+}
+
+static int cgroup_apply_cftypes(struct cftype *cfts, bool is_add)
+{
+	struct cgroup_subsys *ss = cfts[0].ss;
+	struct cgroup *root = &ss->root->cgrp;
+	struct cgroup_subsys_state *css;
+	int ret = 0;
+
+	lockdep_assert_held(&cgroup_mutex);
+
+	/* add/rm files for all cgroups created before */
+	css_for_each_descendant_pre(css, cgroup_css(root, ss)) {
+		struct cgroup *cgrp = css->cgroup;
+
+		if (!(css->flags & CSS_VISIBLE))
+			continue;
+
+		ret = cgroup_addrm_files(css, cgrp, cfts, is_add);
+		if (ret)
+			break;
+	}
+
+	if (is_add && !ret)
+		kernfs_activate(root->kn);
+	return ret;
+}
+
+static void cgroup_exit_cftypes(struct cftype *cfts)
+{
+	struct cftype *cft;
+
+	for (cft = cfts; cft->name[0] != '\0'; cft++) {
+		/* free copy for custom atomic_write_len, see init_cftypes() */
+		if (cft->max_write_len && cft->max_write_len != PAGE_SIZE)
+			kfree(cft->kf_ops);
+		cft->kf_ops = NULL;
+		cft->ss = NULL;
+
+		/* revert flags set by cgroup core while adding @cfts */
+		cft->flags &= ~(__CFTYPE_ONLY_ON_DFL | __CFTYPE_NOT_ON_DFL);
+	}
+}
+
+static int cgroup_init_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
+{
+	struct cftype *cft;
+
+	for (cft = cfts; cft->name[0] != '\0'; cft++) {
+		struct kernfs_ops *kf_ops;
+
+		WARN_ON(cft->ss || cft->kf_ops);
+
+		if (cft->seq_start)
+			kf_ops = &cgroup_kf_ops;
+		else
+			kf_ops = &cgroup_kf_single_ops;
+
+		/*
+		 * Ugh... if @cft wants a custom max_write_len, we need to
+		 * make a copy of kf_ops to set its atomic_write_len.
+		 */
+		if (cft->max_write_len && cft->max_write_len != PAGE_SIZE) {
+			kf_ops = kmemdup(kf_ops, sizeof(*kf_ops), GFP_KERNEL);
+			if (!kf_ops) {
+				cgroup_exit_cftypes(cfts);
+				return -ENOMEM;
+			}
+			kf_ops->atomic_write_len = cft->max_write_len;
+		}
+
+		cft->kf_ops = kf_ops;
+		cft->ss = ss;
+	}
+
+	return 0;
+}
+
+static int cgroup_rm_cftypes_locked(struct cftype *cfts)
+{
+	lockdep_assert_held(&cgroup_mutex);
+
+	if (!cfts || !cfts[0].ss)
+		return -ENOENT;
+
+	list_del(&cfts->node);
+	cgroup_apply_cftypes(cfts, false);
+	cgroup_exit_cftypes(cfts);
+	return 0;
+}
+
+/**
+ * cgroup_rm_cftypes - remove an array of cftypes from a subsystem
+ * @cfts: zero-length name terminated array of cftypes
+ *
+ * Unregister @cfts.  Files described by @cfts are removed from all
+ * existing cgroups and all future cgroups won't have them either.  This
+ * function can be called anytime whether @cfts' subsys is attached or not.
+ *
+ * Returns 0 on successful unregistration, -ENOENT if @cfts is not
+ * registered.
+ */
+int cgroup_rm_cftypes(struct cftype *cfts)
+{
+	int ret;
+
+	mutex_lock(&cgroup_mutex);
+	ret = cgroup_rm_cftypes_locked(cfts);
+	mutex_unlock(&cgroup_mutex);
+	return ret;
+}
+
+/**
+ * cgroup_add_cftypes - add an array of cftypes to a subsystem
+ * @ss: target cgroup subsystem
+ * @cfts: zero-length name terminated array of cftypes
+ *
+ * Register @cfts to @ss.  Files described by @cfts are created for all
+ * existing cgroups to which @ss is attached and all future cgroups will
+ * have them too.  This function can be called anytime whether @ss is
+ * attached or not.
+ *
+ * Returns 0 on successful registration, -errno on failure.  Note that this
+ * function currently returns 0 as long as @cfts registration is successful
+ * even if some file creation attempts on existing cgroups fail.
+ */
+static int cgroup_add_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
+{
+	int ret;
+
+	if (!cgroup_ssid_enabled(ss->id))
+		return 0;
+
+	if (!cfts || cfts[0].name[0] == '\0')
+		return 0;
+
+	ret = cgroup_init_cftypes(ss, cfts);
+	if (ret)
+		return ret;
+
+	mutex_lock(&cgroup_mutex);
+
+	list_add_tail(&cfts->node, &ss->cfts);
+	ret = cgroup_apply_cftypes(cfts, true);
+	if (ret)
+		cgroup_rm_cftypes_locked(cfts);
+
+	mutex_unlock(&cgroup_mutex);
+	return ret;
+}
+
+/**
+ * cgroup_add_dfl_cftypes - add an array of cftypes for default hierarchy
+ * @ss: target cgroup subsystem
+ * @cfts: zero-length name terminated array of cftypes
+ *
+ * Similar to cgroup_add_cftypes() but the added files are only used for
+ * the default hierarchy.
+ */
+int cgroup_add_dfl_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
+{
+	struct cftype *cft;
+
+	for (cft = cfts; cft && cft->name[0] != '\0'; cft++)
+		cft->flags |= __CFTYPE_ONLY_ON_DFL;
+	return cgroup_add_cftypes(ss, cfts);
+}
+
+/**
+ * cgroup_add_legacy_cftypes - add an array of cftypes for legacy hierarchies
+ * @ss: target cgroup subsystem
+ * @cfts: zero-length name terminated array of cftypes
+ *
+ * Similar to cgroup_add_cftypes() but the added files are only used for
+ * the legacy hierarchies.
+ */
+int cgroup_add_legacy_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
+{
+	struct cftype *cft;
+
+	for (cft = cfts; cft && cft->name[0] != '\0'; cft++)
+		cft->flags |= __CFTYPE_NOT_ON_DFL;
+	return cgroup_add_cftypes(ss, cfts);
+}
+
+/**
+ * cgroup_file_notify - generate a file modified event for a cgroup_file
+ * @cfile: target cgroup_file
+ *
+ * @cfile must have been obtained by setting cftype->file_offset.
+ */
+void cgroup_file_notify(struct cgroup_file *cfile)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&cgroup_file_kn_lock, flags);
+	if (cfile->kn) {
+		unsigned long last = cfile->notified_at;
+		unsigned long next = last + CGROUP_FILE_NOTIFY_MIN_INTV;
+
+		if (time_in_range(jiffies, last, next)) {
+			timer_reduce(&cfile->notify_timer, next);
+		} else {
+			kernfs_notify(cfile->kn);
+			cfile->notified_at = jiffies;
+		}
+	}
+	spin_unlock_irqrestore(&cgroup_file_kn_lock, flags);
+}
+
+/**
+ * css_next_child - find the next child of a given css
+ * @pos: the current position (%NULL to initiate traversal)
+ * @parent: css whose children to walk
+ *
+ * This function returns the next child of @parent and should be called
+ * under either cgroup_mutex or RCU read lock.  The only requirement is
+ * that @parent and @pos are accessible.  The next sibling is guaranteed to
+ * be returned regardless of their states.
+ *
+ * If a subsystem synchronizes ->css_online() and the start of iteration, a
+ * css which finished ->css_online() is guaranteed to be visible in the
+ * future iterations and will stay visible until the last reference is put.
+ * A css which hasn't finished ->css_online() or already finished
+ * ->css_offline() may show up during traversal.  It's each subsystem's
+ * responsibility to synchronize against on/offlining.
+ */
+struct cgroup_subsys_state *css_next_child(struct cgroup_subsys_state *pos,
+					   struct cgroup_subsys_state *parent)
+{
+	struct cgroup_subsys_state *next;
+
+	cgroup_assert_mutex_or_rcu_locked();
+
+	/*
+	 * @pos could already have been unlinked from the sibling list.
+	 * Once a cgroup is removed, its ->sibling.next is no longer
+	 * updated when its next sibling changes.  CSS_RELEASED is set when
+	 * @pos is taken off list, at which time its next pointer is valid,
+	 * and, as releases are serialized, the one pointed to by the next
+	 * pointer is guaranteed to not have started release yet.  This
+	 * implies that if we observe !CSS_RELEASED on @pos in this RCU
+	 * critical section, the one pointed to by its next pointer is
+	 * guaranteed to not have finished its RCU grace period even if we
+	 * have dropped rcu_read_lock() inbetween iterations.
+	 *
+	 * If @pos has CSS_RELEASED set, its next pointer can't be
+	 * dereferenced; however, as each css is given a monotonically
+	 * increasing unique serial number and always appended to the
+	 * sibling list, the next one can be found by walking the parent's
+	 * children until the first css with higher serial number than
+	 * @pos's.  While this path can be slower, it happens iff iteration
+	 * races against release and the race window is very small.
+	 */
+	if (!pos) {
+		next = list_entry_rcu(parent->children.next, struct cgroup_subsys_state, sibling);
+	} else if (likely(!(pos->flags & CSS_RELEASED))) {
+		next = list_entry_rcu(pos->sibling.next, struct cgroup_subsys_state, sibling);
+	} else {
+		list_for_each_entry_rcu(next, &parent->children, sibling)
+			if (next->serial_nr > pos->serial_nr)
+				break;
+	}
+
+	/*
+	 * @next, if not pointing to the head, can be dereferenced and is
+	 * the next sibling.
+	 */
+	if (&next->sibling != &parent->children)
+		return next;
+	return NULL;
+}
+
+/**
+ * css_next_descendant_pre - find the next descendant for pre-order walk
+ * @pos: the current position (%NULL to initiate traversal)
+ * @root: css whose descendants to walk
+ *
+ * To be used by css_for_each_descendant_pre().  Find the next descendant
+ * to visit for pre-order traversal of @root's descendants.  @root is
+ * included in the iteration and the first node to be visited.
+ *
+ * While this function requires cgroup_mutex or RCU read locking, it
+ * doesn't require the whole traversal to be contained in a single critical
+ * section.  This function will return the correct next descendant as long
+ * as both @pos and @root are accessible and @pos is a descendant of @root.
+ *
+ * If a subsystem synchronizes ->css_online() and the start of iteration, a
+ * css which finished ->css_online() is guaranteed to be visible in the
+ * future iterations and will stay visible until the last reference is put.
+ * A css which hasn't finished ->css_online() or already finished
+ * ->css_offline() may show up during traversal.  It's each subsystem's
+ * responsibility to synchronize against on/offlining.
+ */
+struct cgroup_subsys_state *
+css_next_descendant_pre(struct cgroup_subsys_state *pos,
+			struct cgroup_subsys_state *root)
+{
+	struct cgroup_subsys_state *next;
+
+	cgroup_assert_mutex_or_rcu_locked();
+
+	/* if first iteration, visit @root */
+	if (!pos)
+		return root;
+
+	/* visit the first child if exists */
+	next = css_next_child(NULL, pos);
+	if (next)
+		return next;
+
+	/* no child, visit my or the closest ancestor's next sibling */
+	while (pos != root) {
+		next = css_next_child(pos, pos->parent);
+		if (next)
+			return next;
+		pos = pos->parent;
+	}
+
+	return NULL;
+}
+
+/**
+ * css_rightmost_descendant - return the rightmost descendant of a css
+ * @pos: css of interest
+ *
+ * Return the rightmost descendant of @pos.  If there's no descendant, @pos
+ * is returned.  This can be used during pre-order traversal to skip
+ * subtree of @pos.
+ *
+ * While this function requires cgroup_mutex or RCU read locking, it
+ * doesn't require the whole traversal to be contained in a single critical
+ * section.  This function will return the correct rightmost descendant as
+ * long as @pos is accessible.
+ */
+struct cgroup_subsys_state *
+css_rightmost_descendant(struct cgroup_subsys_state *pos)
+{
+	struct cgroup_subsys_state *last, *tmp;
+
+	cgroup_assert_mutex_or_rcu_locked();
+
+	do {
+		last = pos;
+		/* ->prev isn't RCU safe, walk ->next till the end */
+		pos = NULL;
+		css_for_each_child(tmp, last)
+			pos = tmp;
+	} while (pos);
+
+	return last;
+}
+
+static struct cgroup_subsys_state *
+css_leftmost_descendant(struct cgroup_subsys_state *pos)
+{
+	struct cgroup_subsys_state *last;
+
+	do {
+		last = pos;
+		pos = css_next_child(NULL, pos);
+	} while (pos);
+
+	return last;
+}
+
+/**
+ * css_next_descendant_post - find the next descendant for post-order walk
+ * @pos: the current position (%NULL to initiate traversal)
+ * @root: css whose descendants to walk
+ *
+ * To be used by css_for_each_descendant_post().  Find the next descendant
+ * to visit for post-order traversal of @root's descendants.  @root is
+ * included in the iteration and the last node to be visited.
+ *
+ * While this function requires cgroup_mutex or RCU read locking, it
+ * doesn't require the whole traversal to be contained in a single critical
+ * section.  This function will return the correct next descendant as long
+ * as both @pos and @cgroup are accessible and @pos is a descendant of
+ * @cgroup.
+ *
+ * If a subsystem synchronizes ->css_online() and the start of iteration, a
+ * css which finished ->css_online() is guaranteed to be visible in the
+ * future iterations and will stay visible until the last reference is put.
+ * A css which hasn't finished ->css_online() or already finished
+ * ->css_offline() may show up during traversal.  It's each subsystem's
+ * responsibility to synchronize against on/offlining.
+ */
+struct cgroup_subsys_state *
+css_next_descendant_post(struct cgroup_subsys_state *pos,
+			 struct cgroup_subsys_state *root)
+{
+	struct cgroup_subsys_state *next;
+
+	cgroup_assert_mutex_or_rcu_locked();
+
+	/* if first iteration, visit leftmost descendant which may be @root */
+	if (!pos)
+		return css_leftmost_descendant(root);
+
+	/* if we visited @root, we're done */
+	if (pos == root)
+		return NULL;
+
+	/* if there's an unvisited sibling, visit its leftmost descendant */
+	next = css_next_child(pos, pos->parent);
+	if (next)
+		return css_leftmost_descendant(next);
+
+	/* no sibling left, visit parent */
+	return pos->parent;
+}
+
+/**
+ * css_has_online_children - does a css have online children
+ * @css: the target css
+ *
+ * Returns %true if @css has any online children; otherwise, %false.  This
+ * function can be called from any context but the caller is responsible
+ * for synchronizing against on/offlining as necessary.
+ */
+bool css_has_online_children(struct cgroup_subsys_state *css)
+{
+	struct cgroup_subsys_state *child;
+	bool ret = false;
+
+	rcu_read_lock();
+	css_for_each_child(child, css) {
+		if (child->flags & CSS_ONLINE) {
+			ret = true;
+			break;
+		}
+	}
+	rcu_read_unlock();
+	return ret;
+}
+
+static struct css_set *css_task_iter_next_css_set(struct css_task_iter *it)
+{
+	struct list_head *l;
+	struct cgrp_cset_link *link;
+	struct css_set *cset;
+
+	lockdep_assert_held(&css_set_lock);
+
+	/* find the next threaded cset */
+	if (it->tcset_pos) {
+		l = it->tcset_pos->next;
+
+		if (l != it->tcset_head) {
+			it->tcset_pos = l;
+			return container_of(l, struct css_set,
+					    threaded_csets_node);
+		}
+
+		it->tcset_pos = NULL;
+	}
+
+	/* find the next cset */
+	l = it->cset_pos;
+	l = l->next;
+	if (l == it->cset_head) {
+		it->cset_pos = NULL;
+		return NULL;
+	}
+
+	if (it->ss) {
+		cset = container_of(l, struct css_set, e_cset_node[it->ss->id]);
+	} else {
+		link = list_entry(l, struct cgrp_cset_link, cset_link);
+		cset = link->cset;
+	}
+
+	it->cset_pos = l;
+
+	/* initialize threaded css_set walking */
+	if (it->flags & CSS_TASK_ITER_THREADED) {
+		if (it->cur_dcset)
+			put_css_set_locked(it->cur_dcset);
+		it->cur_dcset = cset;
+		get_css_set(cset);
+
+		it->tcset_head = &cset->threaded_csets;
+		it->tcset_pos = &cset->threaded_csets;
+	}
+
+	return cset;
+}
+
+/**
+ * css_task_iter_advance_css_set - advance a task itererator to the next css_set
+ * @it: the iterator to advance
+ *
+ * Advance @it to the next css_set to walk.
+ */
+static void css_task_iter_advance_css_set(struct css_task_iter *it)
+{
+	struct css_set *cset;
+
+	lockdep_assert_held(&css_set_lock);
+
+	/* Advance to the next non-empty css_set */
+	do {
+		cset = css_task_iter_next_css_set(it);
+		if (!cset) {
+			it->task_pos = NULL;
+			return;
+		}
+	} while (!css_set_populated(cset) && list_empty(&cset->dying_tasks));
+
+	if (!list_empty(&cset->tasks)) {
+		it->task_pos = cset->tasks.next;
+		it->cur_tasks_head = &cset->tasks;
+	} else if (!list_empty(&cset->mg_tasks)) {
+		it->task_pos = cset->mg_tasks.next;
+		it->cur_tasks_head = &cset->mg_tasks;
+	} else {
+		it->task_pos = cset->dying_tasks.next;
+		it->cur_tasks_head = &cset->dying_tasks;
+	}
+
+	it->tasks_head = &cset->tasks;
+	it->mg_tasks_head = &cset->mg_tasks;
+	it->dying_tasks_head = &cset->dying_tasks;
+
+	/*
+	 * We don't keep css_sets locked across iteration steps and thus
+	 * need to take steps to ensure that iteration can be resumed after
+	 * the lock is re-acquired.  Iteration is performed at two levels -
+	 * css_sets and tasks in them.
+	 *
+	 * Once created, a css_set never leaves its cgroup lists, so a
+	 * pinned css_set is guaranteed to stay put and we can resume
+	 * iteration afterwards.
+	 *
+	 * Tasks may leave @cset across iteration steps.  This is resolved
+	 * by registering each iterator with the css_set currently being
+	 * walked and making css_set_move_task() advance iterators whose
+	 * next task is leaving.
+	 */
+	if (it->cur_cset) {
+		list_del(&it->iters_node);
+		put_css_set_locked(it->cur_cset);
+	}
+	get_css_set(cset);
+	it->cur_cset = cset;
+	list_add(&it->iters_node, &cset->task_iters);
+}
+
+static void css_task_iter_skip(struct css_task_iter *it,
+			       struct task_struct *task)
+{
+	lockdep_assert_held(&css_set_lock);
+
+	if (it->task_pos == &task->cg_list) {
+		it->task_pos = it->task_pos->next;
+		it->flags |= CSS_TASK_ITER_SKIPPED;
+	}
+}
+
+static void css_task_iter_advance(struct css_task_iter *it)
+{
+	struct task_struct *task;
+
+	lockdep_assert_held(&css_set_lock);
+repeat:
+	if (it->task_pos) {
+		/*
+		 * Advance iterator to find next entry.  cset->tasks is
+		 * consumed first and then ->mg_tasks.  After ->mg_tasks,
+		 * we move onto the next cset.
+		 */
+		if (it->flags & CSS_TASK_ITER_SKIPPED)
+			it->flags &= ~CSS_TASK_ITER_SKIPPED;
+		else
+			it->task_pos = it->task_pos->next;
+
+		if (it->task_pos == it->tasks_head) {
+			it->task_pos = it->mg_tasks_head->next;
+			it->cur_tasks_head = it->mg_tasks_head;
+		}
+		if (it->task_pos == it->mg_tasks_head) {
+			it->task_pos = it->dying_tasks_head->next;
+			it->cur_tasks_head = it->dying_tasks_head;
+		}
+		if (it->task_pos == it->dying_tasks_head)
+			css_task_iter_advance_css_set(it);
+	} else {
+		/* called from start, proceed to the first cset */
+		css_task_iter_advance_css_set(it);
+	}
+
+	if (!it->task_pos)
+		return;
+
+	task = list_entry(it->task_pos, struct task_struct, cg_list);
+
+	if (it->flags & CSS_TASK_ITER_PROCS) {
+		/* if PROCS, skip over tasks which aren't group leaders */
+		if (!thread_group_leader(task))
+			goto repeat;
+
+		/* and dying leaders w/o live member threads */
+		if (it->cur_tasks_head == it->dying_tasks_head &&
+		    !atomic_read(&task->signal->live))
+			goto repeat;
+	} else {
+		/* skip all dying ones */
+		if (it->cur_tasks_head == it->dying_tasks_head)
+			goto repeat;
+	}
+}
+
+/**
+ * css_task_iter_start - initiate task iteration
+ * @css: the css to walk tasks of
+ * @flags: CSS_TASK_ITER_* flags
+ * @it: the task iterator to use
+ *
+ * Initiate iteration through the tasks of @css.  The caller can call
+ * css_task_iter_next() to walk through the tasks until the function
+ * returns NULL.  On completion of iteration, css_task_iter_end() must be
+ * called.
+ */
+void css_task_iter_start(struct cgroup_subsys_state *css, unsigned int flags,
+			 struct css_task_iter *it)
+{
+	/* no one should try to iterate before mounting cgroups */
+	WARN_ON_ONCE(!use_task_css_set_links);
+
+	memset(it, 0, sizeof(*it));
+
+	spin_lock_irq(&css_set_lock);
+
+	it->ss = css->ss;
+	it->flags = flags;
+
+	if (it->ss)
+		it->cset_pos = &css->cgroup->e_csets[css->ss->id];
+	else
+		it->cset_pos = &css->cgroup->cset_links;
+
+	it->cset_head = it->cset_pos;
+
+	css_task_iter_advance(it);
+
+	spin_unlock_irq(&css_set_lock);
+}
+
+/**
+ * css_task_iter_next - return the next task for the iterator
+ * @it: the task iterator being iterated
+ *
+ * The "next" function for task iteration.  @it should have been
+ * initialized via css_task_iter_start().  Returns NULL when the iteration
+ * reaches the end.
+ */
+struct task_struct *css_task_iter_next(struct css_task_iter *it)
+{
+	if (it->cur_task) {
+		put_task_struct(it->cur_task);
+		it->cur_task = NULL;
+	}
+
+	spin_lock_irq(&css_set_lock);
+
+	/* @it may be half-advanced by skips, finish advancing */
+	if (it->flags & CSS_TASK_ITER_SKIPPED)
+		css_task_iter_advance(it);
+
+	if (it->task_pos) {
+		it->cur_task = list_entry(it->task_pos, struct task_struct,
+					  cg_list);
+		get_task_struct(it->cur_task);
+		css_task_iter_advance(it);
+	}
+
+	spin_unlock_irq(&css_set_lock);
+
+	return it->cur_task;
+}
+
+/**
+ * css_task_iter_end - finish task iteration
+ * @it: the task iterator to finish
+ *
+ * Finish task iteration started by css_task_iter_start().
+ */
+void css_task_iter_end(struct css_task_iter *it)
+{
+	if (it->cur_cset) {
+		spin_lock_irq(&css_set_lock);
+		list_del(&it->iters_node);
+		put_css_set_locked(it->cur_cset);
+		spin_unlock_irq(&css_set_lock);
+	}
+
+	if (it->cur_dcset)
+		put_css_set(it->cur_dcset);
+
+	if (it->cur_task)
+		put_task_struct(it->cur_task);
+}
+
+static void cgroup_procs_release(struct kernfs_open_file *of)
+{
+	struct cgroup_file_ctx *ctx = of->priv;
+
+	if (ctx->procs.started)
+		css_task_iter_end(&ctx->procs.iter);
+}
+
+static void *cgroup_procs_next(struct seq_file *s, void *v, loff_t *pos)
+{
+	struct kernfs_open_file *of = s->private;
+	struct cgroup_file_ctx *ctx = of->priv;
+
+	if (pos)
+		(*pos)++;
+
+	return css_task_iter_next(&ctx->procs.iter);
+}
+
+static void *__cgroup_procs_start(struct seq_file *s, loff_t *pos,
+				  unsigned int iter_flags)
+{
+	struct kernfs_open_file *of = s->private;
+	struct cgroup *cgrp = seq_css(s)->cgroup;
+	struct cgroup_file_ctx *ctx = of->priv;
+	struct css_task_iter *it = &ctx->procs.iter;
+
+	/*
+	 * When a seq_file is seeked, it's always traversed sequentially
+	 * from position 0, so we can simply keep iterating on !0 *pos.
+	 */
+	if (!ctx->procs.started) {
+		if (WARN_ON_ONCE((*pos)))
+			return ERR_PTR(-EINVAL);
+		css_task_iter_start(&cgrp->self, iter_flags, it);
+		ctx->procs.started = true;
+	} else if (!(*pos)) {
+		css_task_iter_end(it);
+		css_task_iter_start(&cgrp->self, iter_flags, it);
+	} else
+		return it->cur_task;
+
+	return cgroup_procs_next(s, NULL, NULL);
+}
+
+static void *cgroup_procs_start(struct seq_file *s, loff_t *pos)
+{
+	struct cgroup *cgrp = seq_css(s)->cgroup;
+
+	/*
+	 * All processes of a threaded subtree belong to the domain cgroup
+	 * of the subtree.  Only threads can be distributed across the
+	 * subtree.  Reject reads on cgroup.procs in the subtree proper.
+	 * They're always empty anyway.
+	 */
+	if (cgroup_is_threaded(cgrp))
+		return ERR_PTR(-EOPNOTSUPP);
+
+	return __cgroup_procs_start(s, pos, CSS_TASK_ITER_PROCS |
+					    CSS_TASK_ITER_THREADED);
+}
+
+static int cgroup_procs_show(struct seq_file *s, void *v)
+{
+	seq_printf(s, "%d\n", task_pid_vnr(v));
+	return 0;
+}
+
+static int cgroup_procs_write_permission(struct cgroup *src_cgrp,
+					 struct cgroup *dst_cgrp,
+					 struct super_block *sb,
+					 struct cgroup_namespace *ns)
+{
+	struct cgroup *com_cgrp = src_cgrp;
+	struct inode *inode;
+	int ret;
+
+	lockdep_assert_held(&cgroup_mutex);
+
+	/* find the common ancestor */
+	while (!cgroup_is_descendant(dst_cgrp, com_cgrp))
+		com_cgrp = cgroup_parent(com_cgrp);
+
+	/* %current should be authorized to migrate to the common ancestor */
+	inode = kernfs_get_inode(sb, com_cgrp->procs_file.kn);
+	if (!inode)
+		return -ENOMEM;
+
+	ret = inode_permission(inode, MAY_WRITE);
+	iput(inode);
+	if (ret)
+		return ret;
+
+	/*
+	 * If namespaces are delegation boundaries, %current must be able
+	 * to see both source and destination cgroups from its namespace.
+	 */
+	if ((cgrp_dfl_root.flags & CGRP_ROOT_NS_DELEGATE) &&
+	    (!cgroup_is_descendant(src_cgrp, ns->root_cset->dfl_cgrp) ||
+	     !cgroup_is_descendant(dst_cgrp, ns->root_cset->dfl_cgrp)))
+		return -ENOENT;
+
+	return 0;
+}
+
+static ssize_t cgroup_procs_write(struct kernfs_open_file *of,
+				  char *buf, size_t nbytes, loff_t off)
+{
+	struct cgroup_file_ctx *ctx = of->priv;
+	struct cgroup *src_cgrp, *dst_cgrp;
+	struct task_struct *task;
+	const struct cred *saved_cred;
+	ssize_t ret;
+
+	dst_cgrp = cgroup_kn_lock_live(of->kn, false);
+	if (!dst_cgrp)
+		return -ENODEV;
+
+	task = cgroup_procs_write_start(buf, true);
+	ret = PTR_ERR_OR_ZERO(task);
+	if (ret)
+		goto out_unlock;
+
+	/* find the source cgroup */
+	spin_lock_irq(&css_set_lock);
+	src_cgrp = task_cgroup_from_root(task, &cgrp_dfl_root);
+	spin_unlock_irq(&css_set_lock);
+
+	/*
+	 * Process and thread migrations follow same delegation rule. Check
+	 * permissions using the credentials from file open to protect against
+	 * inherited fd attacks.
+	 */
+	saved_cred = override_creds(of->file->f_cred);
+	ret = cgroup_procs_write_permission(src_cgrp, dst_cgrp,
+					    of->file->f_path.dentry->d_sb,
+					    ctx->ns);
+	revert_creds(saved_cred);
+	if (ret)
+		goto out_finish;
+
+	ret = cgroup_attach_task(dst_cgrp, task, true);
+
+out_finish:
+	cgroup_procs_write_finish(task);
+out_unlock:
+	cgroup_kn_unlock(of->kn);
+
+	return ret ?: nbytes;
+}
+
+static void *cgroup_threads_start(struct seq_file *s, loff_t *pos)
+{
+	return __cgroup_procs_start(s, pos, 0);
+}
+
+static ssize_t cgroup_threads_write(struct kernfs_open_file *of,
+				    char *buf, size_t nbytes, loff_t off)
+{
+	struct cgroup_file_ctx *ctx = of->priv;
+	struct cgroup *src_cgrp, *dst_cgrp;
+	struct task_struct *task;
+	const struct cred *saved_cred;
+	ssize_t ret;
+
+	buf = strstrip(buf);
+
+	dst_cgrp = cgroup_kn_lock_live(of->kn, false);
+	if (!dst_cgrp)
+		return -ENODEV;
+
+	task = cgroup_procs_write_start(buf, false);
+	ret = PTR_ERR_OR_ZERO(task);
+	if (ret)
+		goto out_unlock;
+
+	/* find the source cgroup */
+	spin_lock_irq(&css_set_lock);
+	src_cgrp = task_cgroup_from_root(task, &cgrp_dfl_root);
+	spin_unlock_irq(&css_set_lock);
+
+	/*
+	 * Process and thread migrations follow same delegation rule. Check
+	 * permissions using the credentials from file open to protect against
+	 * inherited fd attacks.
+	 */
+	saved_cred = override_creds(of->file->f_cred);
+	ret = cgroup_procs_write_permission(src_cgrp, dst_cgrp,
+					    of->file->f_path.dentry->d_sb,
+					    ctx->ns);
+	revert_creds(saved_cred);
+	if (ret)
+		goto out_finish;
+
+	/* and must be contained in the same domain */
+	ret = -EOPNOTSUPP;
+	if (src_cgrp->dom_cgrp != dst_cgrp->dom_cgrp)
+		goto out_finish;
+
+	ret = cgroup_attach_task(dst_cgrp, task, false);
+
+out_finish:
+	cgroup_procs_write_finish(task);
+out_unlock:
+	cgroup_kn_unlock(of->kn);
+
+	return ret ?: nbytes;
+}
+
+/* cgroup core interface files for the default hierarchy */
+static struct cftype cgroup_base_files[] = {
+	{
+		.name = "cgroup.type",
+		.flags = CFTYPE_NOT_ON_ROOT,
+		.seq_show = cgroup_type_show,
+		.write = cgroup_type_write,
+	},
+	{
+		.name = "cgroup.procs",
+		.flags = CFTYPE_NS_DELEGATABLE,
+		.file_offset = offsetof(struct cgroup, procs_file),
+		.release = cgroup_procs_release,
+		.seq_start = cgroup_procs_start,
+		.seq_next = cgroup_procs_next,
+		.seq_show = cgroup_procs_show,
+		.write = cgroup_procs_write,
+	},
+	{
+		.name = "cgroup.threads",
+		.flags = CFTYPE_NS_DELEGATABLE,
+		.release = cgroup_procs_release,
+		.seq_start = cgroup_threads_start,
+		.seq_next = cgroup_procs_next,
+		.seq_show = cgroup_procs_show,
+		.write = cgroup_threads_write,
+	},
+	{
+		.name = "cgroup.controllers",
+		.seq_show = cgroup_controllers_show,
+	},
+	{
+		.name = "cgroup.subtree_control",
+		.flags = CFTYPE_NS_DELEGATABLE,
+		.seq_show = cgroup_subtree_control_show,
+		.write = cgroup_subtree_control_write,
+	},
+	{
+		.name = "cgroup.events",
+		.flags = CFTYPE_NOT_ON_ROOT,
+		.file_offset = offsetof(struct cgroup, events_file),
+		.seq_show = cgroup_events_show,
+	},
+	{
+		.name = "cgroup.max.descendants",
+		.seq_show = cgroup_max_descendants_show,
+		.write = cgroup_max_descendants_write,
+	},
+	{
+		.name = "cgroup.max.depth",
+		.seq_show = cgroup_max_depth_show,
+		.write = cgroup_max_depth_write,
+	},
+	{
+		.name = "cgroup.stat",
+		.seq_show = cgroup_stat_show,
+	},
+	{
+		.name = "cpu.stat",
+		.flags = CFTYPE_NOT_ON_ROOT,
+		.seq_show = cpu_stat_show,
+	},
+	{ }	/* terminate */
+};
+
+/*
+ * css destruction is four-stage process.
+ *
+ * 1. Destruction starts.  Killing of the percpu_ref is initiated.
+ *    Implemented in kill_css().
+ *
+ * 2. When the percpu_ref is confirmed to be visible as killed on all CPUs
+ *    and thus css_tryget_online() is guaranteed to fail, the css can be
+ *    offlined by invoking offline_css().  After offlining, the base ref is
+ *    put.  Implemented in css_killed_work_fn().
+ *
+ * 3. When the percpu_ref reaches zero, the only possible remaining
+ *    accessors are inside RCU read sections.  css_release() schedules the
+ *    RCU callback.
+ *
+ * 4. After the grace period, the css can be freed.  Implemented in
+ *    css_free_work_fn().
+ *
+ * It is actually hairier because both step 2 and 4 require process context
+ * and thus involve punting to css->destroy_work adding two additional
+ * steps to the already complex sequence.
+ */
+static void css_free_rwork_fn(struct work_struct *work)
+{
+	struct cgroup_subsys_state *css = container_of(to_rcu_work(work),
+				struct cgroup_subsys_state, destroy_rwork);
+	struct cgroup_subsys *ss = css->ss;
+	struct cgroup *cgrp = css->cgroup;
+
+	percpu_ref_exit(&css->refcnt);
+
+	if (ss) {
+		/* css free path */
+		struct cgroup_subsys_state *parent = css->parent;
+		int id = css->id;
+
+		ss->css_free(css);
+		cgroup_idr_remove(&ss->css_idr, id);
+		cgroup_put(cgrp);
+
+		if (parent)
+			css_put(parent);
+	} else {
+		/* cgroup free path */
+		atomic_dec(&cgrp->root->nr_cgrps);
+		cgroup1_pidlist_destroy_all(cgrp);
+		cancel_work_sync(&cgrp->release_agent_work);
+
+		if (cgroup_parent(cgrp)) {
+			/*
+			 * We get a ref to the parent, and put the ref when
+			 * this cgroup is being freed, so it's guaranteed
+			 * that the parent won't be destroyed before its
+			 * children.
+			 */
+			cgroup_put(cgroup_parent(cgrp));
+			kernfs_put(cgrp->kn);
+			if (cgroup_on_dfl(cgrp))
+				cgroup_rstat_exit(cgrp);
+			kfree(cgrp);
+		} else {
+			/*
+			 * This is root cgroup's refcnt reaching zero,
+			 * which indicates that the root should be
+			 * released.
+			 */
+			cgroup_destroy_root(cgrp->root);
+		}
+	}
+}
+
+static void css_release_work_fn(struct work_struct *work)
+{
+	struct cgroup_subsys_state *css =
+		container_of(work, struct cgroup_subsys_state, destroy_work);
+	struct cgroup_subsys *ss = css->ss;
+	struct cgroup *cgrp = css->cgroup;
+
+	mutex_lock(&cgroup_mutex);
+
+	css->flags |= CSS_RELEASED;
+	list_del_rcu(&css->sibling);
+
+	if (ss) {
+		/* css release path */
+		if (!list_empty(&css->rstat_css_node)) {
+			cgroup_rstat_flush(cgrp);
+			list_del_rcu(&css->rstat_css_node);
+		}
+
+		cgroup_idr_replace(&ss->css_idr, NULL, css->id);
+		if (ss->css_released)
+			ss->css_released(css);
+	} else {
+		struct cgroup *tcgrp;
+
+		/* cgroup release path */
+		TRACE_CGROUP_PATH(release, cgrp);
+
+		if (cgroup_on_dfl(cgrp))
+			cgroup_rstat_flush(cgrp);
+
+		spin_lock_irq(&css_set_lock);
+		for (tcgrp = cgroup_parent(cgrp); tcgrp;
+		     tcgrp = cgroup_parent(tcgrp))
+			tcgrp->nr_dying_descendants--;
+		spin_unlock_irq(&css_set_lock);
+
+		cgroup_idr_remove(&cgrp->root->cgroup_idr, cgrp->id);
+		cgrp->id = -1;
+
+		/*
+		 * There are two control paths which try to determine
+		 * cgroup from dentry without going through kernfs -
+		 * cgroupstats_build() and css_tryget_online_from_dir().
+		 * Those are supported by RCU protecting clearing of
+		 * cgrp->kn->priv backpointer.
+		 */
+		if (cgrp->kn)
+			RCU_INIT_POINTER(*(void __rcu __force **)&cgrp->kn->priv,
+					 NULL);
+
+		cgroup_bpf_put(cgrp);
+	}
+
+	mutex_unlock(&cgroup_mutex);
+
+	INIT_RCU_WORK(&css->destroy_rwork, css_free_rwork_fn);
+	queue_rcu_work(cgroup_destroy_wq, &css->destroy_rwork);
+}
+
+static void css_release(struct percpu_ref *ref)
+{
+	struct cgroup_subsys_state *css =
+		container_of(ref, struct cgroup_subsys_state, refcnt);
+
+	INIT_WORK(&css->destroy_work, css_release_work_fn);
+	queue_work(cgroup_destroy_wq, &css->destroy_work);
+}
+
+static void init_and_link_css(struct cgroup_subsys_state *css,
+			      struct cgroup_subsys *ss, struct cgroup *cgrp)
+{
+	lockdep_assert_held(&cgroup_mutex);
+
+	cgroup_get_live(cgrp);
+
+	memset(css, 0, sizeof(*css));
+	css->cgroup = cgrp;
+	css->ss = ss;
+	css->id = -1;
+	INIT_LIST_HEAD(&css->sibling);
+	INIT_LIST_HEAD(&css->children);
+	INIT_LIST_HEAD(&css->rstat_css_node);
+	css->serial_nr = css_serial_nr_next++;
+	atomic_set(&css->online_cnt, 0);
+
+	if (cgroup_parent(cgrp)) {
+		css->parent = cgroup_css(cgroup_parent(cgrp), ss);
+		css_get(css->parent);
+	}
+
+	if (cgroup_on_dfl(cgrp) && ss->css_rstat_flush)
+		list_add_rcu(&css->rstat_css_node, &cgrp->rstat_css_list);
+
+	BUG_ON(cgroup_css(cgrp, ss));
+}
+
+/* invoke ->css_online() on a new CSS and mark it online if successful */
+static int online_css(struct cgroup_subsys_state *css)
+{
+	struct cgroup_subsys *ss = css->ss;
+	int ret = 0;
+
+	lockdep_assert_held(&cgroup_mutex);
+
+	if (ss->css_online)
+		ret = ss->css_online(css);
+	if (!ret) {
+		css->flags |= CSS_ONLINE;
+		rcu_assign_pointer(css->cgroup->subsys[ss->id], css);
+
+		atomic_inc(&css->online_cnt);
+		if (css->parent)
+			atomic_inc(&css->parent->online_cnt);
+	}
+	return ret;
+}
+
+/* if the CSS is online, invoke ->css_offline() on it and mark it offline */
+static void offline_css(struct cgroup_subsys_state *css)
+{
+	struct cgroup_subsys *ss = css->ss;
+
+	lockdep_assert_held(&cgroup_mutex);
+
+	if (!(css->flags & CSS_ONLINE))
+		return;
+
+	if (ss->css_offline)
+		ss->css_offline(css);
+
+	css->flags &= ~CSS_ONLINE;
+	RCU_INIT_POINTER(css->cgroup->subsys[ss->id], NULL);
+
+	wake_up_all(&css->cgroup->offline_waitq);
+}
+
+/**
+ * css_create - create a cgroup_subsys_state
+ * @cgrp: the cgroup new css will be associated with
+ * @ss: the subsys of new css
+ *
+ * Create a new css associated with @cgrp - @ss pair.  On success, the new
+ * css is online and installed in @cgrp.  This function doesn't create the
+ * interface files.  Returns 0 on success, -errno on failure.
+ */
+static struct cgroup_subsys_state *css_create(struct cgroup *cgrp,
+					      struct cgroup_subsys *ss)
+{
+	struct cgroup *parent = cgroup_parent(cgrp);
+	struct cgroup_subsys_state *parent_css = cgroup_css(parent, ss);
+	struct cgroup_subsys_state *css;
+	int err;
+
+	lockdep_assert_held(&cgroup_mutex);
+
+	css = ss->css_alloc(parent_css);
+	if (!css)
+		css = ERR_PTR(-ENOMEM);
+	if (IS_ERR(css))
+		return css;
+
+	init_and_link_css(css, ss, cgrp);
+
+	err = percpu_ref_init(&css->refcnt, css_release, 0, GFP_KERNEL);
+	if (err)
+		goto err_free_css;
+
+	err = cgroup_idr_alloc(&ss->css_idr, NULL, 2, 0, GFP_KERNEL);
+	if (err < 0)
+		goto err_free_css;
+	css->id = err;
+
+	/* @css is ready to be brought online now, make it visible */
+	list_add_tail_rcu(&css->sibling, &parent_css->children);
+	cgroup_idr_replace(&ss->css_idr, css, css->id);
+
+	err = online_css(css);
+	if (err)
+		goto err_list_del;
+
+	if (ss->broken_hierarchy && !ss->warned_broken_hierarchy &&
+	    cgroup_parent(parent)) {
+		pr_warn("%s (%d) created nested cgroup for controller \"%s\" which has incomplete hierarchy support. Nested cgroups may change behavior in the future.\n",
+			current->comm, current->pid, ss->name);
+		if (!strcmp(ss->name, "memory"))
+			pr_warn("\"memory\" requires setting use_hierarchy to 1 on the root\n");
+		ss->warned_broken_hierarchy = true;
+	}
+
+	return css;
+
+err_list_del:
+	list_del_rcu(&css->sibling);
+err_free_css:
+	list_del_rcu(&css->rstat_css_node);
+	INIT_RCU_WORK(&css->destroy_rwork, css_free_rwork_fn);
+	queue_rcu_work(cgroup_destroy_wq, &css->destroy_rwork);
+	return ERR_PTR(err);
+}
+
+/*
+ * The returned cgroup is fully initialized including its control mask, but
+ * it isn't associated with its kernfs_node and doesn't have the control
+ * mask applied.
+ */
+static struct cgroup *cgroup_create(struct cgroup *parent)
+{
+	struct cgroup_root *root = parent->root;
+	struct cgroup *cgrp, *tcgrp;
+	int level = parent->level + 1;
+	int ret;
+
+	/* allocate the cgroup and its ID, 0 is reserved for the root */
+	cgrp = kzalloc(struct_size(cgrp, ancestor_ids, (level + 1)),
+		       GFP_KERNEL);
+	if (!cgrp)
+		return ERR_PTR(-ENOMEM);
+
+	ret = percpu_ref_init(&cgrp->self.refcnt, css_release, 0, GFP_KERNEL);
+	if (ret)
+		goto out_free_cgrp;
+
+	if (cgroup_on_dfl(parent)) {
+		ret = cgroup_rstat_init(cgrp);
+		if (ret)
+			goto out_cancel_ref;
+	}
+
+	/*
+	 * Temporarily set the pointer to NULL, so idr_find() won't return
+	 * a half-baked cgroup.
+	 */
+	cgrp->id = cgroup_idr_alloc(&root->cgroup_idr, NULL, 2, 0, GFP_KERNEL);
+	if (cgrp->id < 0) {
+		ret = -ENOMEM;
+		goto out_stat_exit;
+	}
+
+	init_cgroup_housekeeping(cgrp);
+
+	cgrp->self.parent = &parent->self;
+	cgrp->root = root;
+	cgrp->level = level;
+	ret = cgroup_bpf_inherit(cgrp);
+	if (ret)
+		goto out_idr_free;
+
+	spin_lock_irq(&css_set_lock);
+	for (tcgrp = cgrp; tcgrp; tcgrp = cgroup_parent(tcgrp)) {
+		cgrp->ancestor_ids[tcgrp->level] = tcgrp->id;
+
+		if (tcgrp != cgrp)
+			tcgrp->nr_descendants++;
+	}
+	spin_unlock_irq(&css_set_lock);
+
+	if (notify_on_release(parent))
+		set_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
+
+	if (test_bit(CGRP_CPUSET_CLONE_CHILDREN, &parent->flags))
+		set_bit(CGRP_CPUSET_CLONE_CHILDREN, &cgrp->flags);
+
+	cgrp->self.serial_nr = css_serial_nr_next++;
+
+	/* allocation complete, commit to creation */
+	list_add_tail_rcu(&cgrp->self.sibling, &cgroup_parent(cgrp)->self.children);
+	atomic_inc(&root->nr_cgrps);
+	cgroup_get_live(parent);
+
+	/*
+	 * @cgrp is now fully operational.  If something fails after this
+	 * point, it'll be released via the normal destruction path.
+	 */
+	cgroup_idr_replace(&root->cgroup_idr, cgrp, cgrp->id);
+
+	/*
+	 * On the default hierarchy, a child doesn't automatically inherit
+	 * subtree_control from the parent.  Each is configured manually.
+	 */
+	if (!cgroup_on_dfl(cgrp))
+		cgrp->subtree_control = cgroup_control(cgrp);
+
+	cgroup_propagate_control(cgrp);
+
+	return cgrp;
+
+out_idr_free:
+	cgroup_idr_remove(&root->cgroup_idr, cgrp->id);
+out_stat_exit:
+	if (cgroup_on_dfl(parent))
+		cgroup_rstat_exit(cgrp);
+out_cancel_ref:
+	percpu_ref_exit(&cgrp->self.refcnt);
+out_free_cgrp:
+	kfree(cgrp);
+	return ERR_PTR(ret);
+}
+
+static bool cgroup_check_hierarchy_limits(struct cgroup *parent)
+{
+	struct cgroup *cgroup;
+	int ret = false;
+	int level = 1;
+
+	lockdep_assert_held(&cgroup_mutex);
+
+	for (cgroup = parent; cgroup; cgroup = cgroup_parent(cgroup)) {
+		if (cgroup->nr_descendants >= cgroup->max_descendants)
+			goto fail;
+
+		if (level > cgroup->max_depth)
+			goto fail;
+
+		level++;
+	}
+
+	ret = true;
+fail:
+	return ret;
+}
+
+int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name, umode_t mode)
+{
+	struct cgroup *parent, *cgrp;
+	struct kernfs_node *kn;
+	int ret;
+
+	/* do not accept '\n' to prevent making /proc/<pid>/cgroup unparsable */
+	if (strchr(name, '\n'))
+		return -EINVAL;
+
+	parent = cgroup_kn_lock_live(parent_kn, false);
+	if (!parent)
+		return -ENODEV;
+
+	if (!cgroup_check_hierarchy_limits(parent)) {
+		ret = -EAGAIN;
+		goto out_unlock;
+	}
+
+	cgrp = cgroup_create(parent);
+	if (IS_ERR(cgrp)) {
+		ret = PTR_ERR(cgrp);
+		goto out_unlock;
+	}
+
+	/* create the directory */
+	kn = kernfs_create_dir(parent->kn, name, mode, cgrp);
+	if (IS_ERR(kn)) {
+		ret = PTR_ERR(kn);
+		goto out_destroy;
+	}
+	cgrp->kn = kn;
+
+	/*
+	 * This extra ref will be put in cgroup_free_fn() and guarantees
+	 * that @cgrp->kn is always accessible.
+	 */
+	kernfs_get(kn);
+
+	ret = cgroup_kn_set_ugid(kn);
+	if (ret)
+		goto out_destroy;
+
+	ret = css_populate_dir(&cgrp->self);
+	if (ret)
+		goto out_destroy;
+
+	ret = cgroup_apply_control_enable(cgrp);
+	if (ret)
+		goto out_destroy;
+
+	TRACE_CGROUP_PATH(mkdir, cgrp);
+
+	/* let's create and online css's */
+	kernfs_activate(kn);
+
+	ret = 0;
+	goto out_unlock;
+
+out_destroy:
+	cgroup_destroy_locked(cgrp);
+out_unlock:
+	cgroup_kn_unlock(parent_kn);
+	return ret;
+}
+
+/*
+ * This is called when the refcnt of a css is confirmed to be killed.
+ * css_tryget_online() is now guaranteed to fail.  Tell the subsystem to
+ * initate destruction and put the css ref from kill_css().
+ */
+static void css_killed_work_fn(struct work_struct *work)
+{
+	struct cgroup_subsys_state *css =
+		container_of(work, struct cgroup_subsys_state, destroy_work);
+
+	mutex_lock(&cgroup_mutex);
+
+	do {
+		offline_css(css);
+		css_put(css);
+		/* @css can't go away while we're holding cgroup_mutex */
+		css = css->parent;
+	} while (css && atomic_dec_and_test(&css->online_cnt));
+
+	mutex_unlock(&cgroup_mutex);
+}
+
+/* css kill confirmation processing requires process context, bounce */
+static void css_killed_ref_fn(struct percpu_ref *ref)
+{
+	struct cgroup_subsys_state *css =
+		container_of(ref, struct cgroup_subsys_state, refcnt);
+
+	if (atomic_dec_and_test(&css->online_cnt)) {
+		INIT_WORK(&css->destroy_work, css_killed_work_fn);
+		queue_work(cgroup_destroy_wq, &css->destroy_work);
+	}
+}
+
+/**
+ * kill_css - destroy a css
+ * @css: css to destroy
+ *
+ * This function initiates destruction of @css by removing cgroup interface
+ * files and putting its base reference.  ->css_offline() will be invoked
+ * asynchronously once css_tryget_online() is guaranteed to fail and when
+ * the reference count reaches zero, @css will be released.
+ */
+static void kill_css(struct cgroup_subsys_state *css)
+{
+	lockdep_assert_held(&cgroup_mutex);
+
+	if (css->flags & CSS_DYING)
+		return;
+
+	css->flags |= CSS_DYING;
+
+	/*
+	 * This must happen before css is disassociated with its cgroup.
+	 * See seq_css() for details.
+	 */
+	css_clear_dir(css);
+
+	/*
+	 * Killing would put the base ref, but we need to keep it alive
+	 * until after ->css_offline().
+	 */
+	css_get(css);
+
+	/*
+	 * cgroup core guarantees that, by the time ->css_offline() is
+	 * invoked, no new css reference will be given out via
+	 * css_tryget_online().  We can't simply call percpu_ref_kill() and
+	 * proceed to offlining css's because percpu_ref_kill() doesn't
+	 * guarantee that the ref is seen as killed on all CPUs on return.
+	 *
+	 * Use percpu_ref_kill_and_confirm() to get notifications as each
+	 * css is confirmed to be seen as killed on all CPUs.
+	 */
+	percpu_ref_kill_and_confirm(&css->refcnt, css_killed_ref_fn);
+}
+
+/**
+ * cgroup_destroy_locked - the first stage of cgroup destruction
+ * @cgrp: cgroup to be destroyed
+ *
+ * css's make use of percpu refcnts whose killing latency shouldn't be
+ * exposed to userland and are RCU protected.  Also, cgroup core needs to
+ * guarantee that css_tryget_online() won't succeed by the time
+ * ->css_offline() is invoked.  To satisfy all the requirements,
+ * destruction is implemented in the following two steps.
+ *
+ * s1. Verify @cgrp can be destroyed and mark it dying.  Remove all
+ *     userland visible parts and start killing the percpu refcnts of
+ *     css's.  Set up so that the next stage will be kicked off once all
+ *     the percpu refcnts are confirmed to be killed.
+ *
+ * s2. Invoke ->css_offline(), mark the cgroup dead and proceed with the
+ *     rest of destruction.  Once all cgroup references are gone, the
+ *     cgroup is RCU-freed.
+ *
+ * This function implements s1.  After this step, @cgrp is gone as far as
+ * the userland is concerned and a new cgroup with the same name may be
+ * created.  As cgroup doesn't care about the names internally, this
+ * doesn't cause any problem.
+ */
+static int cgroup_destroy_locked(struct cgroup *cgrp)
+	__releases(&cgroup_mutex) __acquires(&cgroup_mutex)
+{
+	struct cgroup *tcgrp, *parent = cgroup_parent(cgrp);
+	struct cgroup_subsys_state *css;
+	struct cgrp_cset_link *link;
+	int ssid;
+
+	lockdep_assert_held(&cgroup_mutex);
+
+	/*
+	 * Only migration can raise populated from zero and we're already
+	 * holding cgroup_mutex.
+	 */
+	if (cgroup_is_populated(cgrp))
+		return -EBUSY;
+
+	/*
+	 * Make sure there's no live children.  We can't test emptiness of
+	 * ->self.children as dead children linger on it while being
+	 * drained; otherwise, "rmdir parent/child parent" may fail.
+	 */
+	if (css_has_online_children(&cgrp->self))
+		return -EBUSY;
+
+	/*
+	 * Mark @cgrp and the associated csets dead.  The former prevents
+	 * further task migration and child creation by disabling
+	 * cgroup_lock_live_group().  The latter makes the csets ignored by
+	 * the migration path.
+	 */
+	cgrp->self.flags &= ~CSS_ONLINE;
+
+	spin_lock_irq(&css_set_lock);
+	list_for_each_entry(link, &cgrp->cset_links, cset_link)
+		link->cset->dead = true;
+	spin_unlock_irq(&css_set_lock);
+
+	/* initiate massacre of all css's */
+	for_each_css(css, ssid, cgrp)
+		kill_css(css);
+
+	/* clear and remove @cgrp dir, @cgrp has an extra ref on its kn */
+	css_clear_dir(&cgrp->self);
+	kernfs_remove(cgrp->kn);
+
+	if (parent && cgroup_is_threaded(cgrp))
+		parent->nr_threaded_children--;
+
+	spin_lock_irq(&css_set_lock);
+	for (tcgrp = cgroup_parent(cgrp); tcgrp; tcgrp = cgroup_parent(tcgrp)) {
+		tcgrp->nr_descendants--;
+		tcgrp->nr_dying_descendants++;
+	}
+	spin_unlock_irq(&css_set_lock);
+
+	cgroup1_check_for_release(parent);
+
+	/* put the base reference */
+	percpu_ref_kill(&cgrp->self.refcnt);
+
+	return 0;
+};
+
+int cgroup_rmdir(struct kernfs_node *kn)
+{
+	struct cgroup *cgrp;
+	int ret = 0;
+
+	cgrp = cgroup_kn_lock_live(kn, false);
+	if (!cgrp)
+		return 0;
+
+	ret = cgroup_destroy_locked(cgrp);
+	if (!ret)
+		TRACE_CGROUP_PATH(rmdir, cgrp);
+
+	cgroup_kn_unlock(kn);
+	return ret;
+}
+
+static struct kernfs_syscall_ops cgroup_kf_syscall_ops = {
+	.show_options		= cgroup_show_options,
+	.remount_fs		= cgroup_remount,
+	.mkdir			= cgroup_mkdir,
+	.rmdir			= cgroup_rmdir,
+	.show_path		= cgroup_show_path,
+};
+
+static void __init cgroup_init_subsys(struct cgroup_subsys *ss, bool early)
+{
+	struct cgroup_subsys_state *css;
+
+	pr_debug("Initializing cgroup subsys %s\n", ss->name);
+
+	mutex_lock(&cgroup_mutex);
+
+	idr_init(&ss->css_idr);
+	INIT_LIST_HEAD(&ss->cfts);
+
+	/* Create the root cgroup state for this subsystem */
+	ss->root = &cgrp_dfl_root;
+	css = ss->css_alloc(cgroup_css(&cgrp_dfl_root.cgrp, ss));
+	/* We don't handle early failures gracefully */
+	BUG_ON(IS_ERR(css));
+	init_and_link_css(css, ss, &cgrp_dfl_root.cgrp);
+
+	/*
+	 * Root csses are never destroyed and we can't initialize
+	 * percpu_ref during early init.  Disable refcnting.
+	 */
+	css->flags |= CSS_NO_REF;
+
+	if (early) {
+		/* allocation can't be done safely during early init */
+		css->id = 1;
+	} else {
+		css->id = cgroup_idr_alloc(&ss->css_idr, css, 1, 2, GFP_KERNEL);
+		BUG_ON(css->id < 0);
+	}
+
+	/* Update the init_css_set to contain a subsys
+	 * pointer to this state - since the subsystem is
+	 * newly registered, all tasks and hence the
+	 * init_css_set is in the subsystem's root cgroup. */
+	init_css_set.subsys[ss->id] = css;
+
+	have_fork_callback |= (bool)ss->fork << ss->id;
+	have_exit_callback |= (bool)ss->exit << ss->id;
+	have_release_callback |= (bool)ss->release << ss->id;
+	have_canfork_callback |= (bool)ss->can_fork << ss->id;
+
+	/* At system boot, before all subsystems have been
+	 * registered, no tasks have been forked, so we don't
+	 * need to invoke fork callbacks here. */
+	BUG_ON(!list_empty(&init_task.tasks));
+
+	BUG_ON(online_css(css));
+
+	mutex_unlock(&cgroup_mutex);
+}
+
+/**
+ * cgroup_init_early - cgroup initialization at system boot
+ *
+ * Initialize cgroups at system boot, and initialize any
+ * subsystems that request early init.
+ */
+int __init cgroup_init_early(void)
+{
+	static struct cgroup_sb_opts __initdata opts;
+	struct cgroup_subsys *ss;
+	int i;
+
+	init_cgroup_root(&cgrp_dfl_root, &opts);
+	cgrp_dfl_root.cgrp.self.flags |= CSS_NO_REF;
+
+	RCU_INIT_POINTER(init_task.cgroups, &init_css_set);
+
+	for_each_subsys(ss, i) {
+		WARN(!ss->css_alloc || !ss->css_free || ss->name || ss->id,
+		     "invalid cgroup_subsys %d:%s css_alloc=%p css_free=%p id:name=%d:%s\n",
+		     i, cgroup_subsys_name[i], ss->css_alloc, ss->css_free,
+		     ss->id, ss->name);
+		WARN(strlen(cgroup_subsys_name[i]) > MAX_CGROUP_TYPE_NAMELEN,
+		     "cgroup_subsys_name %s too long\n", cgroup_subsys_name[i]);
+
+		ss->id = i;
+		ss->name = cgroup_subsys_name[i];
+		if (!ss->legacy_name)
+			ss->legacy_name = cgroup_subsys_name[i];
+
+		if (ss->early_init)
+			cgroup_init_subsys(ss, true);
+	}
+	return 0;
+}
+
+/**
+ * cgroup_init - cgroup initialization
+ *
+ * Register cgroup filesystem and /proc file, and initialize
+ * any subsystems that didn't request early init.
+ */
+int __init cgroup_init(void)
+{
+	struct cgroup_subsys *ss;
+	int ssid;
+
+	BUILD_BUG_ON(CGROUP_SUBSYS_COUNT > 16);
+	BUG_ON(percpu_init_rwsem(&cgroup_threadgroup_rwsem));
+	BUG_ON(cgroup_init_cftypes(NULL, cgroup_base_files));
+	BUG_ON(cgroup_init_cftypes(NULL, cgroup1_base_files));
+
+	cgroup_rstat_boot();
+
+	/*
+	 * The latency of the synchronize_sched() is too high for cgroups,
+	 * avoid it at the cost of forcing all readers into the slow path.
+	 */
+	rcu_sync_enter_start(&cgroup_threadgroup_rwsem.rss);
+
+	get_user_ns(init_cgroup_ns.user_ns);
+
+	mutex_lock(&cgroup_mutex);
+
+	/*
+	 * Add init_css_set to the hash table so that dfl_root can link to
+	 * it during init.
+	 */
+	hash_add(css_set_table, &init_css_set.hlist,
+		 css_set_hash(init_css_set.subsys));
+
+	BUG_ON(cgroup_setup_root(&cgrp_dfl_root, 0, 0));
+
+	mutex_unlock(&cgroup_mutex);
+
+	for_each_subsys(ss, ssid) {
+		if (ss->early_init) {
+			struct cgroup_subsys_state *css =
+				init_css_set.subsys[ss->id];
+
+			css->id = cgroup_idr_alloc(&ss->css_idr, css, 1, 2,
+						   GFP_KERNEL);
+			BUG_ON(css->id < 0);
+		} else {
+			cgroup_init_subsys(ss, false);
+		}
+
+		list_add_tail(&init_css_set.e_cset_node[ssid],
+			      &cgrp_dfl_root.cgrp.e_csets[ssid]);
+
+		/*
+		 * Setting dfl_root subsys_mask needs to consider the
+		 * disabled flag and cftype registration needs kmalloc,
+		 * both of which aren't available during early_init.
+		 */
+		if (!cgroup_ssid_enabled(ssid))
+			continue;
+
+		if (cgroup1_ssid_disabled(ssid))
+			printk(KERN_INFO "Disabling %s control group subsystem in v1 mounts\n",
+			       ss->name);
+
+		cgrp_dfl_root.subsys_mask |= 1 << ss->id;
+
+		/* implicit controllers must be threaded too */
+		WARN_ON(ss->implicit_on_dfl && !ss->threaded);
+
+		if (ss->implicit_on_dfl)
+			cgrp_dfl_implicit_ss_mask |= 1 << ss->id;
+		else if (!ss->dfl_cftypes)
+			cgrp_dfl_inhibit_ss_mask |= 1 << ss->id;
+
+		if (ss->threaded)
+			cgrp_dfl_threaded_ss_mask |= 1 << ss->id;
+
+		if (ss->dfl_cftypes == ss->legacy_cftypes) {
+			WARN_ON(cgroup_add_cftypes(ss, ss->dfl_cftypes));
+		} else {
+			WARN_ON(cgroup_add_dfl_cftypes(ss, ss->dfl_cftypes));
+			WARN_ON(cgroup_add_legacy_cftypes(ss, ss->legacy_cftypes));
+		}
+
+		if (ss->bind)
+			ss->bind(init_css_set.subsys[ssid]);
+
+		mutex_lock(&cgroup_mutex);
+		css_populate_dir(init_css_set.subsys[ssid]);
+		mutex_unlock(&cgroup_mutex);
+	}
+
+	/* init_css_set.subsys[] has been updated, re-hash */
+	hash_del(&init_css_set.hlist);
+	hash_add(css_set_table, &init_css_set.hlist,
+		 css_set_hash(init_css_set.subsys));
+
+	WARN_ON(sysfs_create_mount_point(fs_kobj, "cgroup"));
+	WARN_ON(register_filesystem(&cgroup_fs_type));
+	WARN_ON(register_filesystem(&cgroup2_fs_type));
+	WARN_ON(!proc_create_single("cgroups", 0, NULL, proc_cgroupstats_show));
+
+	return 0;
+}
+
+static int __init cgroup_wq_init(void)
+{
+	/*
+	 * There isn't much point in executing destruction path in
+	 * parallel.  Good chunk is serialized with cgroup_mutex anyway.
+	 * Use 1 for @max_active.
+	 *
+	 * We would prefer to do this in cgroup_init() above, but that
+	 * is called before init_workqueues(): so leave this until after.
+	 */
+	cgroup_destroy_wq = alloc_workqueue("cgroup_destroy", 0, 1);
+	BUG_ON(!cgroup_destroy_wq);
+	return 0;
+}
+core_initcall(cgroup_wq_init);
+
+void cgroup_path_from_kernfs_id(const union kernfs_node_id *id,
+					char *buf, size_t buflen)
+{
+	struct kernfs_node *kn;
+
+	kn = kernfs_get_node_by_id(cgrp_dfl_root.kf_root, id);
+	if (!kn)
+		return;
+	kernfs_path(kn, buf, buflen);
+	kernfs_put(kn);
+}
+
+/*
+ * proc_cgroup_show()
+ *  - Print task's cgroup paths into seq_file, one line for each hierarchy
+ *  - Used for /proc/<pid>/cgroup.
+ */
+int proc_cgroup_show(struct seq_file *m, struct pid_namespace *ns,
+		     struct pid *pid, struct task_struct *tsk)
+{
+	char *buf;
+	int retval;
+	struct cgroup_root *root;
+
+	retval = -ENOMEM;
+	buf = kmalloc(PATH_MAX, GFP_KERNEL);
+	if (!buf)
+		goto out;
+
+	mutex_lock(&cgroup_mutex);
+	spin_lock_irq(&css_set_lock);
+
+	for_each_root(root) {
+		struct cgroup_subsys *ss;
+		struct cgroup *cgrp;
+		int ssid, count = 0;
+
+		if (root == &cgrp_dfl_root && !cgrp_dfl_visible)
+			continue;
+
+		seq_printf(m, "%d:", root->hierarchy_id);
+		if (root != &cgrp_dfl_root)
+			for_each_subsys(ss, ssid)
+				if (root->subsys_mask & (1 << ssid))
+					seq_printf(m, "%s%s", count++ ? "," : "",
+						   ss->legacy_name);
+		if (strlen(root->name))
+			seq_printf(m, "%sname=%s", count ? "," : "",
+				   root->name);
+		seq_putc(m, ':');
+
+		cgrp = task_cgroup_from_root(tsk, root);
+
+		/*
+		 * On traditional hierarchies, all zombie tasks show up as
+		 * belonging to the root cgroup.  On the default hierarchy,
+		 * while a zombie doesn't show up in "cgroup.procs" and
+		 * thus can't be migrated, its /proc/PID/cgroup keeps
+		 * reporting the cgroup it belonged to before exiting.  If
+		 * the cgroup is removed before the zombie is reaped,
+		 * " (deleted)" is appended to the cgroup path.
+		 */
+		if (cgroup_on_dfl(cgrp) || !(tsk->flags & PF_EXITING)) {
+			retval = cgroup_path_ns_locked(cgrp, buf, PATH_MAX,
+						current->nsproxy->cgroup_ns);
+			if (retval >= PATH_MAX)
+				retval = -ENAMETOOLONG;
+			if (retval < 0)
+				goto out_unlock;
+
+			seq_puts(m, buf);
+		} else {
+			seq_puts(m, "/");
+		}
+
+		if (cgroup_on_dfl(cgrp) && cgroup_is_dead(cgrp))
+			seq_puts(m, " (deleted)\n");
+		else
+			seq_putc(m, '\n');
+	}
+
+	retval = 0;
+out_unlock:
+	spin_unlock_irq(&css_set_lock);
+	mutex_unlock(&cgroup_mutex);
+	kfree(buf);
+out:
+	return retval;
+}
+
+/**
+ * cgroup_fork - initialize cgroup related fields during copy_process()
+ * @child: pointer to task_struct of forking parent process.
+ *
+ * A task is associated with the init_css_set until cgroup_post_fork()
+ * attaches it to the parent's css_set.  Empty cg_list indicates that
+ * @child isn't holding reference to its css_set.
+ */
+void cgroup_fork(struct task_struct *child)
+{
+	RCU_INIT_POINTER(child->cgroups, &init_css_set);
+	INIT_LIST_HEAD(&child->cg_list);
+}
+
+/**
+ * cgroup_can_fork - called on a new task before the process is exposed
+ * @child: the task in question.
+ *
+ * This calls the subsystem can_fork() callbacks. If the can_fork() callback
+ * returns an error, the fork aborts with that error code. This allows for
+ * a cgroup subsystem to conditionally allow or deny new forks.
+ */
+int cgroup_can_fork(struct task_struct *child)
+{
+	struct cgroup_subsys *ss;
+	int i, j, ret;
+
+	do_each_subsys_mask(ss, i, have_canfork_callback) {
+		ret = ss->can_fork(child);
+		if (ret)
+			goto out_revert;
+	} while_each_subsys_mask();
+
+	return 0;
+
+out_revert:
+	for_each_subsys(ss, j) {
+		if (j >= i)
+			break;
+		if (ss->cancel_fork)
+			ss->cancel_fork(child);
+	}
+
+	return ret;
+}
+
+/**
+ * cgroup_cancel_fork - called if a fork failed after cgroup_can_fork()
+ * @child: the task in question
+ *
+ * This calls the cancel_fork() callbacks if a fork failed *after*
+ * cgroup_can_fork() succeded.
+ */
+void cgroup_cancel_fork(struct task_struct *child)
+{
+	struct cgroup_subsys *ss;
+	int i;
+
+	for_each_subsys(ss, i)
+		if (ss->cancel_fork)
+			ss->cancel_fork(child);
+}
+
+/**
+ * cgroup_post_fork - called on a new task after adding it to the task list
+ * @child: the task in question
+ *
+ * Adds the task to the list running through its css_set if necessary and
+ * call the subsystem fork() callbacks.  Has to be after the task is
+ * visible on the task list in case we race with the first call to
+ * cgroup_task_iter_start() - to guarantee that the new task ends up on its
+ * list.
+ */
+void cgroup_post_fork(struct task_struct *child)
+{
+	struct cgroup_subsys *ss;
+	int i;
+
+	/*
+	 * This may race against cgroup_enable_task_cg_lists().  As that
+	 * function sets use_task_css_set_links before grabbing
+	 * tasklist_lock and we just went through tasklist_lock to add
+	 * @child, it's guaranteed that either we see the set
+	 * use_task_css_set_links or cgroup_enable_task_cg_lists() sees
+	 * @child during its iteration.
+	 *
+	 * If we won the race, @child is associated with %current's
+	 * css_set.  Grabbing css_set_lock guarantees both that the
+	 * association is stable, and, on completion of the parent's
+	 * migration, @child is visible in the source of migration or
+	 * already in the destination cgroup.  This guarantee is necessary
+	 * when implementing operations which need to migrate all tasks of
+	 * a cgroup to another.
+	 *
+	 * Note that if we lose to cgroup_enable_task_cg_lists(), @child
+	 * will remain in init_css_set.  This is safe because all tasks are
+	 * in the init_css_set before cg_links is enabled and there's no
+	 * operation which transfers all tasks out of init_css_set.
+	 */
+	if (use_task_css_set_links) {
+		struct css_set *cset;
+
+		spin_lock_irq(&css_set_lock);
+		cset = task_css_set(current);
+		if (list_empty(&child->cg_list)) {
+			get_css_set(cset);
+			cset->nr_tasks++;
+			css_set_move_task(child, NULL, cset, false);
+		}
+		spin_unlock_irq(&css_set_lock);
+	}
+
+	/*
+	 * Call ss->fork().  This must happen after @child is linked on
+	 * css_set; otherwise, @child might change state between ->fork()
+	 * and addition to css_set.
+	 */
+	do_each_subsys_mask(ss, i, have_fork_callback) {
+		ss->fork(child);
+	} while_each_subsys_mask();
+}
+
+/**
+ * cgroup_exit - detach cgroup from exiting task
+ * @tsk: pointer to task_struct of exiting process
+ *
+ * Description: Detach cgroup from @tsk and release it.
+ *
+ * Note that cgroups marked notify_on_release force every task in
+ * them to take the global cgroup_mutex mutex when exiting.
+ * This could impact scaling on very large systems.  Be reluctant to
+ * use notify_on_release cgroups where very high task exit scaling
+ * is required on large systems.
+ *
+ * We set the exiting tasks cgroup to the root cgroup (top_cgroup).  We
+ * call cgroup_exit() while the task is still competent to handle
+ * notify_on_release(), then leave the task attached to the root cgroup in
+ * each hierarchy for the remainder of its exit.  No need to bother with
+ * init_css_set refcnting.  init_css_set never goes away and we can't race
+ * with migration path - PF_EXITING is visible to migration path.
+ */
+void cgroup_exit(struct task_struct *tsk)
+{
+	struct cgroup_subsys *ss;
+	struct css_set *cset;
+	int i;
+
+	/*
+	 * Unlink from @tsk from its css_set.  As migration path can't race
+	 * with us, we can check css_set and cg_list without synchronization.
+	 */
+	cset = task_css_set(tsk);
+
+	if (!list_empty(&tsk->cg_list)) {
+		spin_lock_irq(&css_set_lock);
+		css_set_move_task(tsk, cset, NULL, false);
+		list_add_tail(&tsk->cg_list, &cset->dying_tasks);
+		cset->nr_tasks--;
+		spin_unlock_irq(&css_set_lock);
+	} else {
+		get_css_set(cset);
+	}
+
+	/* see cgroup_post_fork() for details */
+	do_each_subsys_mask(ss, i, have_exit_callback) {
+		ss->exit(tsk);
+	} while_each_subsys_mask();
+}
+
+void cgroup_release(struct task_struct *task)
+{
+	struct cgroup_subsys *ss;
+	int ssid;
+
+	do_each_subsys_mask(ss, ssid, have_release_callback) {
+		ss->release(task);
+	} while_each_subsys_mask();
+
+	if (use_task_css_set_links) {
+		spin_lock_irq(&css_set_lock);
+		css_set_skip_task_iters(task_css_set(task), task);
+		list_del_init(&task->cg_list);
+		spin_unlock_irq(&css_set_lock);
+	}
+}
+
+void cgroup_free(struct task_struct *task)
+{
+	struct css_set *cset = task_css_set(task);
+	put_css_set(cset);
+}
+
+static int __init cgroup_disable(char *str)
+{
+	struct cgroup_subsys *ss;
+	char *token;
+	int i;
+
+	while ((token = strsep(&str, ",")) != NULL) {
+		if (!*token)
+			continue;
+
+		for_each_subsys(ss, i) {
+			if (strcmp(token, ss->name) &&
+			    strcmp(token, ss->legacy_name))
+				continue;
+
+			static_branch_disable(cgroup_subsys_enabled_key[i]);
+			pr_info("Disabling %s control group subsystem\n",
+				ss->name);
+		}
+	}
+	return 1;
+}
+__setup("cgroup_disable=", cgroup_disable);
+
+/**
+ * css_tryget_online_from_dir - get corresponding css from a cgroup dentry
+ * @dentry: directory dentry of interest
+ * @ss: subsystem of interest
+ *
+ * If @dentry is a directory for a cgroup which has @ss enabled on it, try
+ * to get the corresponding css and return it.  If such css doesn't exist
+ * or can't be pinned, an ERR_PTR value is returned.
+ */
+struct cgroup_subsys_state *css_tryget_online_from_dir(struct dentry *dentry,
+						       struct cgroup_subsys *ss)
+{
+	struct kernfs_node *kn = kernfs_node_from_dentry(dentry);
+	struct file_system_type *s_type = dentry->d_sb->s_type;
+	struct cgroup_subsys_state *css = NULL;
+	struct cgroup *cgrp;
+
+	/* is @dentry a cgroup dir? */
+	if ((s_type != &cgroup_fs_type && s_type != &cgroup2_fs_type) ||
+	    !kn || kernfs_type(kn) != KERNFS_DIR)
+		return ERR_PTR(-EBADF);
+
+	rcu_read_lock();
+
+	/*
+	 * This path doesn't originate from kernfs and @kn could already
+	 * have been or be removed at any point.  @kn->priv is RCU
+	 * protected for this access.  See css_release_work_fn() for details.
+	 */
+	cgrp = rcu_dereference(*(void __rcu __force **)&kn->priv);
+	if (cgrp)
+		css = cgroup_css(cgrp, ss);
+
+	if (!css || !css_tryget_online(css))
+		css = ERR_PTR(-ENOENT);
+
+	rcu_read_unlock();
+	return css;
+}
+
+/**
+ * css_from_id - lookup css by id
+ * @id: the cgroup id
+ * @ss: cgroup subsys to be looked into
+ *
+ * Returns the css if there's valid one with @id, otherwise returns NULL.
+ * Should be called under rcu_read_lock().
+ */
+struct cgroup_subsys_state *css_from_id(int id, struct cgroup_subsys *ss)
+{
+	WARN_ON_ONCE(!rcu_read_lock_held());
+	return idr_find(&ss->css_idr, id);
+}
+
+/**
+ * cgroup_get_from_path - lookup and get a cgroup from its default hierarchy path
+ * @path: path on the default hierarchy
+ *
+ * Find the cgroup at @path on the default hierarchy, increment its
+ * reference count and return it.  Returns pointer to the found cgroup on
+ * success, ERR_PTR(-ENOENT) if @path doens't exist and ERR_PTR(-ENOTDIR)
+ * if @path points to a non-directory.
+ */
+struct cgroup *cgroup_get_from_path(const char *path)
+{
+	struct kernfs_node *kn;
+	struct cgroup *cgrp;
+
+	mutex_lock(&cgroup_mutex);
+
+	kn = kernfs_walk_and_get(cgrp_dfl_root.cgrp.kn, path);
+	if (kn) {
+		if (kernfs_type(kn) == KERNFS_DIR) {
+			cgrp = kn->priv;
+			cgroup_get_live(cgrp);
+		} else {
+			cgrp = ERR_PTR(-ENOTDIR);
+		}
+		kernfs_put(kn);
+	} else {
+		cgrp = ERR_PTR(-ENOENT);
+	}
+
+	mutex_unlock(&cgroup_mutex);
+	return cgrp;
+}
+EXPORT_SYMBOL_GPL(cgroup_get_from_path);
+
+/**
+ * cgroup_get_from_fd - get a cgroup pointer from a fd
+ * @fd: fd obtained by open(cgroup2_dir)
+ *
+ * Find the cgroup from a fd which should be obtained
+ * by opening a cgroup directory.  Returns a pointer to the
+ * cgroup on success. ERR_PTR is returned if the cgroup
+ * cannot be found.
+ */
+struct cgroup *cgroup_get_from_fd(int fd)
+{
+	struct cgroup_subsys_state *css;
+	struct cgroup *cgrp;
+	struct file *f;
+
+	f = fget_raw(fd);
+	if (!f)
+		return ERR_PTR(-EBADF);
+
+	css = css_tryget_online_from_dir(f->f_path.dentry, NULL);
+	fput(f);
+	if (IS_ERR(css))
+		return ERR_CAST(css);
+
+	cgrp = css->cgroup;
+	if (!cgroup_on_dfl(cgrp)) {
+		cgroup_put(cgrp);
+		return ERR_PTR(-EBADF);
+	}
+
+	return cgrp;
+}
+EXPORT_SYMBOL_GPL(cgroup_get_from_fd);
+
+/*
+ * sock->sk_cgrp_data handling.  For more info, see sock_cgroup_data
+ * definition in cgroup-defs.h.
+ */
+#ifdef CONFIG_SOCK_CGROUP_DATA
+
+#if defined(CONFIG_CGROUP_NET_PRIO) || defined(CONFIG_CGROUP_NET_CLASSID)
+
+DEFINE_SPINLOCK(cgroup_sk_update_lock);
+static bool cgroup_sk_alloc_disabled __read_mostly;
+
+void cgroup_sk_alloc_disable(void)
+{
+	if (cgroup_sk_alloc_disabled)
+		return;
+	pr_info("cgroup: disabling cgroup2 socket matching due to net_prio or net_cls activation\n");
+	cgroup_sk_alloc_disabled = true;
+}
+
+#else
+
+#define cgroup_sk_alloc_disabled	false
+
+#endif
+
+void cgroup_sk_alloc(struct sock_cgroup_data *skcd)
+{
+	if (cgroup_sk_alloc_disabled) {
+		skcd->no_refcnt = 1;
+		return;
+	}
+
+	/* Don't associate the sock with unrelated interrupted task's cgroup. */
+	if (in_interrupt())
+		return;
+
+	rcu_read_lock();
+
+	while (true) {
+		struct css_set *cset;
+
+		cset = task_css_set(current);
+		if (likely(cgroup_tryget(cset->dfl_cgrp))) {
+			skcd->val = (unsigned long)cset->dfl_cgrp;
+			break;
+		}
+		cpu_relax();
+	}
+
+	rcu_read_unlock();
+}
+
+void cgroup_sk_clone(struct sock_cgroup_data *skcd)
+{
+	/* Socket clone path */
+	if (skcd->val) {
+		if (skcd->no_refcnt)
+			return;
+		/*
+		 * We might be cloning a socket which is left in an empty
+		 * cgroup and the cgroup might have already been rmdir'd.
+		 * Don't use cgroup_get_live().
+		 */
+		cgroup_get(sock_cgroup_ptr(skcd));
+	}
+}
+
+void cgroup_sk_free(struct sock_cgroup_data *skcd)
+{
+	if (skcd->no_refcnt)
+		return;
+
+	cgroup_put(sock_cgroup_ptr(skcd));
+}
+
+#endif	/* CONFIG_SOCK_CGROUP_DATA */
+
+#ifdef CONFIG_CGROUP_BPF
+int cgroup_bpf_attach(struct cgroup *cgrp, struct bpf_prog *prog,
+		      enum bpf_attach_type type, u32 flags)
+{
+	int ret;
+
+	mutex_lock(&cgroup_mutex);
+	ret = __cgroup_bpf_attach(cgrp, prog, type, flags);
+	mutex_unlock(&cgroup_mutex);
+	return ret;
+}
+int cgroup_bpf_detach(struct cgroup *cgrp, struct bpf_prog *prog,
+		      enum bpf_attach_type type, u32 flags)
+{
+	int ret;
+
+	mutex_lock(&cgroup_mutex);
+	ret = __cgroup_bpf_detach(cgrp, prog, type, flags);
+	mutex_unlock(&cgroup_mutex);
+	return ret;
+}
+int cgroup_bpf_query(struct cgroup *cgrp, const union bpf_attr *attr,
+		     union bpf_attr __user *uattr)
+{
+	int ret;
+
+	mutex_lock(&cgroup_mutex);
+	ret = __cgroup_bpf_query(cgrp, attr, uattr);
+	mutex_unlock(&cgroup_mutex);
+	return ret;
+}
+#endif /* CONFIG_CGROUP_BPF */
+
+#ifdef CONFIG_SYSFS
+static ssize_t show_delegatable_files(struct cftype *files, char *buf,
+				      ssize_t size, const char *prefix)
+{
+	struct cftype *cft;
+	ssize_t ret = 0;
+
+	for (cft = files; cft && cft->name[0] != '\0'; cft++) {
+		if (!(cft->flags & CFTYPE_NS_DELEGATABLE))
+			continue;
+
+		if (prefix)
+			ret += snprintf(buf + ret, size - ret, "%s.", prefix);
+
+		ret += snprintf(buf + ret, size - ret, "%s\n", cft->name);
+
+		if (unlikely(ret >= size)) {
+			WARN_ON(1);
+			break;
+		}
+	}
+
+	return ret;
+}
+
+static ssize_t delegate_show(struct kobject *kobj, struct kobj_attribute *attr,
+			      char *buf)
+{
+	struct cgroup_subsys *ss;
+	int ssid;
+	ssize_t ret = 0;
+
+	ret = show_delegatable_files(cgroup_base_files, buf, PAGE_SIZE - ret,
+				     NULL);
+
+	for_each_subsys(ss, ssid)
+		ret += show_delegatable_files(ss->dfl_cftypes, buf + ret,
+					      PAGE_SIZE - ret,
+					      cgroup_subsys_name[ssid]);
+
+	return ret;
+}
+static struct kobj_attribute cgroup_delegate_attr = __ATTR_RO(delegate);
+
+static ssize_t features_show(struct kobject *kobj, struct kobj_attribute *attr,
+			     char *buf)
+{
+	return snprintf(buf, PAGE_SIZE, "nsdelegate\n");
+}
+static struct kobj_attribute cgroup_features_attr = __ATTR_RO(features);
+
+static struct attribute *cgroup_sysfs_attrs[] = {
+	&cgroup_delegate_attr.attr,
+	&cgroup_features_attr.attr,
+	NULL,
+};
+
+static const struct attribute_group cgroup_sysfs_attr_group = {
+	.attrs = cgroup_sysfs_attrs,
+	.name = "cgroup",
+};
+
+static int __init cgroup_sysfs_init(void)
+{
+	return sysfs_create_group(kernel_kobj, &cgroup_sysfs_attr_group);
+}
+subsys_initcall(cgroup_sysfs_init);
+#endif /* CONFIG_SYSFS */
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
new file mode 100644
index 000000000..dcd5755b1
--- /dev/null
+++ b/kernel/cgroup/cpuset.c
@@ -0,0 +1,2779 @@
+/*
+ *  kernel/cpuset.c
+ *
+ *  Processor and Memory placement constraints for sets of tasks.
+ *
+ *  Copyright (C) 2003 BULL SA.
+ *  Copyright (C) 2004-2007 Silicon Graphics, Inc.
+ *  Copyright (C) 2006 Google, Inc
+ *
+ *  Portions derived from Patrick Mochel's sysfs code.
+ *  sysfs is Copyright (c) 2001-3 Patrick Mochel
+ *
+ *  2003-10-10 Written by Simon Derr.
+ *  2003-10-22 Updates by Stephen Hemminger.
+ *  2004 May-July Rework by Paul Jackson.
+ *  2006 Rework by Paul Menage to use generic cgroups
+ *  2008 Rework of the scheduler domains and CPU hotplug handling
+ *       by Max Krasnyansky
+ *
+ *  This file is subject to the terms and conditions of the GNU General Public
+ *  License.  See the file COPYING in the main directory of the Linux
+ *  distribution for more details.
+ */
+
+#include <linux/cpu.h>
+#include <linux/cpumask.h>
+#include <linux/cpuset.h>
+#include <linux/err.h>
+#include <linux/errno.h>
+#include <linux/file.h>
+#include <linux/fs.h>
+#include <linux/init.h>
+#include <linux/interrupt.h>
+#include <linux/kernel.h>
+#include <linux/kmod.h>
+#include <linux/list.h>
+#include <linux/mempolicy.h>
+#include <linux/mm.h>
+#include <linux/memory.h>
+#include <linux/export.h>
+#include <linux/mount.h>
+#include <linux/namei.h>
+#include <linux/pagemap.h>
+#include <linux/proc_fs.h>
+#include <linux/rcupdate.h>
+#include <linux/sched.h>
+#include <linux/sched/mm.h>
+#include <linux/sched/task.h>
+#include <linux/seq_file.h>
+#include <linux/security.h>
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+#include <linux/stat.h>
+#include <linux/string.h>
+#include <linux/time.h>
+#include <linux/time64.h>
+#include <linux/backing-dev.h>
+#include <linux/sort.h>
+#include <linux/oom.h>
+#include <linux/sched/isolation.h>
+#include <linux/uaccess.h>
+#include <linux/atomic.h>
+#include <linux/mutex.h>
+#include <linux/cgroup.h>
+#include <linux/wait.h>
+
+DEFINE_STATIC_KEY_FALSE(cpusets_pre_enable_key);
+DEFINE_STATIC_KEY_FALSE(cpusets_enabled_key);
+
+/* See "Frequency meter" comments, below. */
+
+struct fmeter {
+	int cnt;		/* unprocessed events count */
+	int val;		/* most recent output value */
+	time64_t time;		/* clock (secs) when val computed */
+	spinlock_t lock;	/* guards read or write of above */
+};
+
+struct cpuset {
+	struct cgroup_subsys_state css;
+
+	unsigned long flags;		/* "unsigned long" so bitops work */
+
+	/*
+	 * On default hierarchy:
+	 *
+	 * The user-configured masks can only be changed by writing to
+	 * cpuset.cpus and cpuset.mems, and won't be limited by the
+	 * parent masks.
+	 *
+	 * The effective masks is the real masks that apply to the tasks
+	 * in the cpuset. They may be changed if the configured masks are
+	 * changed or hotplug happens.
+	 *
+	 * effective_mask == configured_mask & parent's effective_mask,
+	 * and if it ends up empty, it will inherit the parent's mask.
+	 *
+	 *
+	 * On legacy hierachy:
+	 *
+	 * The user-configured masks are always the same with effective masks.
+	 */
+
+	/* user-configured CPUs and Memory Nodes allow to tasks */
+	cpumask_var_t cpus_allowed;
+	nodemask_t mems_allowed;
+
+	/* effective CPUs and Memory Nodes allow to tasks */
+	cpumask_var_t effective_cpus;
+	nodemask_t effective_mems;
+
+	/*
+	 * This is old Memory Nodes tasks took on.
+	 *
+	 * - top_cpuset.old_mems_allowed is initialized to mems_allowed.
+	 * - A new cpuset's old_mems_allowed is initialized when some
+	 *   task is moved into it.
+	 * - old_mems_allowed is used in cpuset_migrate_mm() when we change
+	 *   cpuset.mems_allowed and have tasks' nodemask updated, and
+	 *   then old_mems_allowed is updated to mems_allowed.
+	 */
+	nodemask_t old_mems_allowed;
+
+	struct fmeter fmeter;		/* memory_pressure filter */
+
+	/*
+	 * Tasks are being attached to this cpuset.  Used to prevent
+	 * zeroing cpus/mems_allowed between ->can_attach() and ->attach().
+	 */
+	int attach_in_progress;
+
+	/* partition number for rebuild_sched_domains() */
+	int pn;
+
+	/* for custom sched domain */
+	int relax_domain_level;
+};
+
+static inline struct cpuset *css_cs(struct cgroup_subsys_state *css)
+{
+	return css ? container_of(css, struct cpuset, css) : NULL;
+}
+
+/* Retrieve the cpuset for a task */
+static inline struct cpuset *task_cs(struct task_struct *task)
+{
+	return css_cs(task_css(task, cpuset_cgrp_id));
+}
+
+static inline struct cpuset *parent_cs(struct cpuset *cs)
+{
+	return css_cs(cs->css.parent);
+}
+
+#ifdef CONFIG_NUMA
+static inline bool task_has_mempolicy(struct task_struct *task)
+{
+	return task->mempolicy;
+}
+#else
+static inline bool task_has_mempolicy(struct task_struct *task)
+{
+	return false;
+}
+#endif
+
+
+/* bits in struct cpuset flags field */
+typedef enum {
+	CS_ONLINE,
+	CS_CPU_EXCLUSIVE,
+	CS_MEM_EXCLUSIVE,
+	CS_MEM_HARDWALL,
+	CS_MEMORY_MIGRATE,
+	CS_SCHED_LOAD_BALANCE,
+	CS_SPREAD_PAGE,
+	CS_SPREAD_SLAB,
+} cpuset_flagbits_t;
+
+/* convenient tests for these bits */
+static inline bool is_cpuset_online(struct cpuset *cs)
+{
+	return test_bit(CS_ONLINE, &cs->flags) && !css_is_dying(&cs->css);
+}
+
+static inline int is_cpu_exclusive(const struct cpuset *cs)
+{
+	return test_bit(CS_CPU_EXCLUSIVE, &cs->flags);
+}
+
+static inline int is_mem_exclusive(const struct cpuset *cs)
+{
+	return test_bit(CS_MEM_EXCLUSIVE, &cs->flags);
+}
+
+static inline int is_mem_hardwall(const struct cpuset *cs)
+{
+	return test_bit(CS_MEM_HARDWALL, &cs->flags);
+}
+
+static inline int is_sched_load_balance(const struct cpuset *cs)
+{
+	return test_bit(CS_SCHED_LOAD_BALANCE, &cs->flags);
+}
+
+static inline int is_memory_migrate(const struct cpuset *cs)
+{
+	return test_bit(CS_MEMORY_MIGRATE, &cs->flags);
+}
+
+static inline int is_spread_page(const struct cpuset *cs)
+{
+	return test_bit(CS_SPREAD_PAGE, &cs->flags);
+}
+
+static inline int is_spread_slab(const struct cpuset *cs)
+{
+	return test_bit(CS_SPREAD_SLAB, &cs->flags);
+}
+
+static struct cpuset top_cpuset = {
+	.flags = ((1 << CS_ONLINE) | (1 << CS_CPU_EXCLUSIVE) |
+		  (1 << CS_MEM_EXCLUSIVE)),
+};
+
+/**
+ * cpuset_for_each_child - traverse online children of a cpuset
+ * @child_cs: loop cursor pointing to the current child
+ * @pos_css: used for iteration
+ * @parent_cs: target cpuset to walk children of
+ *
+ * Walk @child_cs through the online children of @parent_cs.  Must be used
+ * with RCU read locked.
+ */
+#define cpuset_for_each_child(child_cs, pos_css, parent_cs)		\
+	css_for_each_child((pos_css), &(parent_cs)->css)		\
+		if (is_cpuset_online(((child_cs) = css_cs((pos_css)))))
+
+/**
+ * cpuset_for_each_descendant_pre - pre-order walk of a cpuset's descendants
+ * @des_cs: loop cursor pointing to the current descendant
+ * @pos_css: used for iteration
+ * @root_cs: target cpuset to walk ancestor of
+ *
+ * Walk @des_cs through the online descendants of @root_cs.  Must be used
+ * with RCU read locked.  The caller may modify @pos_css by calling
+ * css_rightmost_descendant() to skip subtree.  @root_cs is included in the
+ * iteration and the first node to be visited.
+ */
+#define cpuset_for_each_descendant_pre(des_cs, pos_css, root_cs)	\
+	css_for_each_descendant_pre((pos_css), &(root_cs)->css)		\
+		if (is_cpuset_online(((des_cs) = css_cs((pos_css)))))
+
+/*
+ * There are two global locks guarding cpuset structures - cpuset_mutex and
+ * callback_lock. We also require taking task_lock() when dereferencing a
+ * task's cpuset pointer. See "The task_lock() exception", at the end of this
+ * comment.
+ *
+ * A task must hold both locks to modify cpusets.  If a task holds
+ * cpuset_mutex, then it blocks others wanting that mutex, ensuring that it
+ * is the only task able to also acquire callback_lock and be able to
+ * modify cpusets.  It can perform various checks on the cpuset structure
+ * first, knowing nothing will change.  It can also allocate memory while
+ * just holding cpuset_mutex.  While it is performing these checks, various
+ * callback routines can briefly acquire callback_lock to query cpusets.
+ * Once it is ready to make the changes, it takes callback_lock, blocking
+ * everyone else.
+ *
+ * Calls to the kernel memory allocator can not be made while holding
+ * callback_lock, as that would risk double tripping on callback_lock
+ * from one of the callbacks into the cpuset code from within
+ * __alloc_pages().
+ *
+ * If a task is only holding callback_lock, then it has read-only
+ * access to cpusets.
+ *
+ * Now, the task_struct fields mems_allowed and mempolicy may be changed
+ * by other task, we use alloc_lock in the task_struct fields to protect
+ * them.
+ *
+ * The cpuset_common_file_read() handlers only hold callback_lock across
+ * small pieces of code, such as when reading out possibly multi-word
+ * cpumasks and nodemasks.
+ *
+ * Accessing a task's cpuset should be done in accordance with the
+ * guidelines for accessing subsystem state in kernel/cgroup.c
+ */
+
+static DEFINE_MUTEX(cpuset_mutex);
+static DEFINE_SPINLOCK(callback_lock);
+
+static struct workqueue_struct *cpuset_migrate_mm_wq;
+
+/*
+ * CPU / memory hotplug is handled asynchronously.
+ */
+static void cpuset_hotplug_workfn(struct work_struct *work);
+static DECLARE_WORK(cpuset_hotplug_work, cpuset_hotplug_workfn);
+
+static DECLARE_WAIT_QUEUE_HEAD(cpuset_attach_wq);
+
+/*
+ * Cgroup v2 behavior is used when on default hierarchy or the
+ * cgroup_v2_mode flag is set.
+ */
+static inline bool is_in_v2_mode(void)
+{
+	return cgroup_subsys_on_dfl(cpuset_cgrp_subsys) ||
+	      (cpuset_cgrp_subsys.root->flags & CGRP_ROOT_CPUSET_V2_MODE);
+}
+
+/*
+ * This is ugly, but preserves the userspace API for existing cpuset
+ * users. If someone tries to mount the "cpuset" filesystem, we
+ * silently switch it to mount "cgroup" instead
+ */
+static struct dentry *cpuset_mount(struct file_system_type *fs_type,
+			 int flags, const char *unused_dev_name, void *data)
+{
+	struct file_system_type *cgroup_fs = get_fs_type("cgroup");
+	struct dentry *ret = ERR_PTR(-ENODEV);
+	if (cgroup_fs) {
+		char mountopts[] =
+			"cpuset,noprefix,"
+			"release_agent=/sbin/cpuset_release_agent";
+		ret = cgroup_fs->mount(cgroup_fs, flags,
+					   unused_dev_name, mountopts);
+		put_filesystem(cgroup_fs);
+	}
+	return ret;
+}
+
+static struct file_system_type cpuset_fs_type = {
+	.name = "cpuset",
+	.mount = cpuset_mount,
+};
+
+/*
+ * Return in pmask the portion of a cpusets's cpus_allowed that
+ * are online.  If none are online, walk up the cpuset hierarchy
+ * until we find one that does have some online cpus.
+ *
+ * One way or another, we guarantee to return some non-empty subset
+ * of cpu_online_mask.
+ *
+ * Call with callback_lock or cpuset_mutex held.
+ */
+static void guarantee_online_cpus(struct cpuset *cs, struct cpumask *pmask)
+{
+	while (!cpumask_intersects(cs->effective_cpus, cpu_online_mask)) {
+		cs = parent_cs(cs);
+		if (unlikely(!cs)) {
+			/*
+			 * The top cpuset doesn't have any online cpu as a
+			 * consequence of a race between cpuset_hotplug_work
+			 * and cpu hotplug notifier.  But we know the top
+			 * cpuset's effective_cpus is on its way to to be
+			 * identical to cpu_online_mask.
+			 */
+			cpumask_copy(pmask, cpu_online_mask);
+			return;
+		}
+	}
+	cpumask_and(pmask, cs->effective_cpus, cpu_online_mask);
+}
+
+/*
+ * Return in *pmask the portion of a cpusets's mems_allowed that
+ * are online, with memory.  If none are online with memory, walk
+ * up the cpuset hierarchy until we find one that does have some
+ * online mems.  The top cpuset always has some mems online.
+ *
+ * One way or another, we guarantee to return some non-empty subset
+ * of node_states[N_MEMORY].
+ *
+ * Call with callback_lock or cpuset_mutex held.
+ */
+static void guarantee_online_mems(struct cpuset *cs, nodemask_t *pmask)
+{
+	while (!nodes_intersects(cs->effective_mems, node_states[N_MEMORY]))
+		cs = parent_cs(cs);
+	nodes_and(*pmask, cs->effective_mems, node_states[N_MEMORY]);
+}
+
+/*
+ * update task's spread flag if cpuset's page/slab spread flag is set
+ *
+ * Call with callback_lock or cpuset_mutex held.
+ */
+static void cpuset_update_task_spread_flag(struct cpuset *cs,
+					struct task_struct *tsk)
+{
+	if (is_spread_page(cs))
+		task_set_spread_page(tsk);
+	else
+		task_clear_spread_page(tsk);
+
+	if (is_spread_slab(cs))
+		task_set_spread_slab(tsk);
+	else
+		task_clear_spread_slab(tsk);
+}
+
+/*
+ * is_cpuset_subset(p, q) - Is cpuset p a subset of cpuset q?
+ *
+ * One cpuset is a subset of another if all its allowed CPUs and
+ * Memory Nodes are a subset of the other, and its exclusive flags
+ * are only set if the other's are set.  Call holding cpuset_mutex.
+ */
+
+static int is_cpuset_subset(const struct cpuset *p, const struct cpuset *q)
+{
+	return	cpumask_subset(p->cpus_allowed, q->cpus_allowed) &&
+		nodes_subset(p->mems_allowed, q->mems_allowed) &&
+		is_cpu_exclusive(p) <= is_cpu_exclusive(q) &&
+		is_mem_exclusive(p) <= is_mem_exclusive(q);
+}
+
+/**
+ * alloc_trial_cpuset - allocate a trial cpuset
+ * @cs: the cpuset that the trial cpuset duplicates
+ */
+static struct cpuset *alloc_trial_cpuset(struct cpuset *cs)
+{
+	struct cpuset *trial;
+
+	trial = kmemdup(cs, sizeof(*cs), GFP_KERNEL);
+	if (!trial)
+		return NULL;
+
+	if (!alloc_cpumask_var(&trial->cpus_allowed, GFP_KERNEL))
+		goto free_cs;
+	if (!alloc_cpumask_var(&trial->effective_cpus, GFP_KERNEL))
+		goto free_cpus;
+
+	cpumask_copy(trial->cpus_allowed, cs->cpus_allowed);
+	cpumask_copy(trial->effective_cpus, cs->effective_cpus);
+	return trial;
+
+free_cpus:
+	free_cpumask_var(trial->cpus_allowed);
+free_cs:
+	kfree(trial);
+	return NULL;
+}
+
+/**
+ * free_trial_cpuset - free the trial cpuset
+ * @trial: the trial cpuset to be freed
+ */
+static void free_trial_cpuset(struct cpuset *trial)
+{
+	free_cpumask_var(trial->effective_cpus);
+	free_cpumask_var(trial->cpus_allowed);
+	kfree(trial);
+}
+
+/*
+ * validate_change() - Used to validate that any proposed cpuset change
+ *		       follows the structural rules for cpusets.
+ *
+ * If we replaced the flag and mask values of the current cpuset
+ * (cur) with those values in the trial cpuset (trial), would
+ * our various subset and exclusive rules still be valid?  Presumes
+ * cpuset_mutex held.
+ *
+ * 'cur' is the address of an actual, in-use cpuset.  Operations
+ * such as list traversal that depend on the actual address of the
+ * cpuset in the list must use cur below, not trial.
+ *
+ * 'trial' is the address of bulk structure copy of cur, with
+ * perhaps one or more of the fields cpus_allowed, mems_allowed,
+ * or flags changed to new, trial values.
+ *
+ * Return 0 if valid, -errno if not.
+ */
+
+static int validate_change(struct cpuset *cur, struct cpuset *trial)
+{
+	struct cgroup_subsys_state *css;
+	struct cpuset *c, *par;
+	int ret;
+
+	rcu_read_lock();
+
+	/* Each of our child cpusets must be a subset of us */
+	ret = -EBUSY;
+	cpuset_for_each_child(c, css, cur)
+		if (!is_cpuset_subset(c, trial))
+			goto out;
+
+	/* Remaining checks don't apply to root cpuset */
+	ret = 0;
+	if (cur == &top_cpuset)
+		goto out;
+
+	par = parent_cs(cur);
+
+	/* On legacy hiearchy, we must be a subset of our parent cpuset. */
+	ret = -EACCES;
+	if (!is_in_v2_mode() && !is_cpuset_subset(trial, par))
+		goto out;
+
+	/*
+	 * If either I or some sibling (!= me) is exclusive, we can't
+	 * overlap
+	 */
+	ret = -EINVAL;
+	cpuset_for_each_child(c, css, par) {
+		if ((is_cpu_exclusive(trial) || is_cpu_exclusive(c)) &&
+		    c != cur &&
+		    cpumask_intersects(trial->cpus_allowed, c->cpus_allowed))
+			goto out;
+		if ((is_mem_exclusive(trial) || is_mem_exclusive(c)) &&
+		    c != cur &&
+		    nodes_intersects(trial->mems_allowed, c->mems_allowed))
+			goto out;
+	}
+
+	/*
+	 * Cpusets with tasks - existing or newly being attached - can't
+	 * be changed to have empty cpus_allowed or mems_allowed.
+	 */
+	ret = -ENOSPC;
+	if ((cgroup_is_populated(cur->css.cgroup) || cur->attach_in_progress)) {
+		if (!cpumask_empty(cur->cpus_allowed) &&
+		    cpumask_empty(trial->cpus_allowed))
+			goto out;
+		if (!nodes_empty(cur->mems_allowed) &&
+		    nodes_empty(trial->mems_allowed))
+			goto out;
+	}
+
+	/*
+	 * We can't shrink if we won't have enough room for SCHED_DEADLINE
+	 * tasks.
+	 */
+	ret = -EBUSY;
+	if (is_cpu_exclusive(cur) &&
+	    !cpuset_cpumask_can_shrink(cur->cpus_allowed,
+				       trial->cpus_allowed))
+		goto out;
+
+	ret = 0;
+out:
+	rcu_read_unlock();
+	return ret;
+}
+
+#ifdef CONFIG_SMP
+/*
+ * Helper routine for generate_sched_domains().
+ * Do cpusets a, b have overlapping effective cpus_allowed masks?
+ */
+static int cpusets_overlap(struct cpuset *a, struct cpuset *b)
+{
+	return cpumask_intersects(a->effective_cpus, b->effective_cpus);
+}
+
+static void
+update_domain_attr(struct sched_domain_attr *dattr, struct cpuset *c)
+{
+	if (dattr->relax_domain_level < c->relax_domain_level)
+		dattr->relax_domain_level = c->relax_domain_level;
+	return;
+}
+
+static void update_domain_attr_tree(struct sched_domain_attr *dattr,
+				    struct cpuset *root_cs)
+{
+	struct cpuset *cp;
+	struct cgroup_subsys_state *pos_css;
+
+	rcu_read_lock();
+	cpuset_for_each_descendant_pre(cp, pos_css, root_cs) {
+		/* skip the whole subtree if @cp doesn't have any CPU */
+		if (cpumask_empty(cp->cpus_allowed)) {
+			pos_css = css_rightmost_descendant(pos_css);
+			continue;
+		}
+
+		if (is_sched_load_balance(cp))
+			update_domain_attr(dattr, cp);
+	}
+	rcu_read_unlock();
+}
+
+/* Must be called with cpuset_mutex held.  */
+static inline int nr_cpusets(void)
+{
+	/* jump label reference count + the top-level cpuset */
+	return static_key_count(&cpusets_enabled_key.key) + 1;
+}
+
+/*
+ * generate_sched_domains()
+ *
+ * This function builds a partial partition of the systems CPUs
+ * A 'partial partition' is a set of non-overlapping subsets whose
+ * union is a subset of that set.
+ * The output of this function needs to be passed to kernel/sched/core.c
+ * partition_sched_domains() routine, which will rebuild the scheduler's
+ * load balancing domains (sched domains) as specified by that partial
+ * partition.
+ *
+ * See "What is sched_load_balance" in Documentation/cgroup-v1/cpusets.txt
+ * for a background explanation of this.
+ *
+ * Does not return errors, on the theory that the callers of this
+ * routine would rather not worry about failures to rebuild sched
+ * domains when operating in the severe memory shortage situations
+ * that could cause allocation failures below.
+ *
+ * Must be called with cpuset_mutex held.
+ *
+ * The three key local variables below are:
+ *    q  - a linked-list queue of cpuset pointers, used to implement a
+ *	   top-down scan of all cpusets.  This scan loads a pointer
+ *	   to each cpuset marked is_sched_load_balance into the
+ *	   array 'csa'.  For our purposes, rebuilding the schedulers
+ *	   sched domains, we can ignore !is_sched_load_balance cpusets.
+ *  csa  - (for CpuSet Array) Array of pointers to all the cpusets
+ *	   that need to be load balanced, for convenient iterative
+ *	   access by the subsequent code that finds the best partition,
+ *	   i.e the set of domains (subsets) of CPUs such that the
+ *	   cpus_allowed of every cpuset marked is_sched_load_balance
+ *	   is a subset of one of these domains, while there are as
+ *	   many such domains as possible, each as small as possible.
+ * doms  - Conversion of 'csa' to an array of cpumasks, for passing to
+ *	   the kernel/sched/core.c routine partition_sched_domains() in a
+ *	   convenient format, that can be easily compared to the prior
+ *	   value to determine what partition elements (sched domains)
+ *	   were changed (added or removed.)
+ *
+ * Finding the best partition (set of domains):
+ *	The triple nested loops below over i, j, k scan over the
+ *	load balanced cpusets (using the array of cpuset pointers in
+ *	csa[]) looking for pairs of cpusets that have overlapping
+ *	cpus_allowed, but which don't have the same 'pn' partition
+ *	number and gives them in the same partition number.  It keeps
+ *	looping on the 'restart' label until it can no longer find
+ *	any such pairs.
+ *
+ *	The union of the cpus_allowed masks from the set of
+ *	all cpusets having the same 'pn' value then form the one
+ *	element of the partition (one sched domain) to be passed to
+ *	partition_sched_domains().
+ */
+static int generate_sched_domains(cpumask_var_t **domains,
+			struct sched_domain_attr **attributes)
+{
+	struct cpuset *cp;	/* scans q */
+	struct cpuset **csa;	/* array of all cpuset ptrs */
+	int csn;		/* how many cpuset ptrs in csa so far */
+	int i, j, k;		/* indices for partition finding loops */
+	cpumask_var_t *doms;	/* resulting partition; i.e. sched domains */
+	struct sched_domain_attr *dattr;  /* attributes for custom domains */
+	int ndoms = 0;		/* number of sched domains in result */
+	int nslot;		/* next empty doms[] struct cpumask slot */
+	struct cgroup_subsys_state *pos_css;
+
+	doms = NULL;
+	dattr = NULL;
+	csa = NULL;
+
+	/* Special case for the 99% of systems with one, full, sched domain */
+	if (is_sched_load_balance(&top_cpuset)) {
+		ndoms = 1;
+		doms = alloc_sched_domains(ndoms);
+		if (!doms)
+			goto done;
+
+		dattr = kmalloc(sizeof(struct sched_domain_attr), GFP_KERNEL);
+		if (dattr) {
+			*dattr = SD_ATTR_INIT;
+			update_domain_attr_tree(dattr, &top_cpuset);
+		}
+		cpumask_and(doms[0], top_cpuset.effective_cpus,
+			    housekeeping_cpumask(HK_FLAG_DOMAIN));
+
+		goto done;
+	}
+
+	csa = kmalloc_array(nr_cpusets(), sizeof(cp), GFP_KERNEL);
+	if (!csa)
+		goto done;
+	csn = 0;
+
+	rcu_read_lock();
+	cpuset_for_each_descendant_pre(cp, pos_css, &top_cpuset) {
+		if (cp == &top_cpuset)
+			continue;
+		/*
+		 * Continue traversing beyond @cp iff @cp has some CPUs and
+		 * isn't load balancing.  The former is obvious.  The
+		 * latter: All child cpusets contain a subset of the
+		 * parent's cpus, so just skip them, and then we call
+		 * update_domain_attr_tree() to calc relax_domain_level of
+		 * the corresponding sched domain.
+		 */
+		if (!cpumask_empty(cp->cpus_allowed) &&
+		    !(is_sched_load_balance(cp) &&
+		      cpumask_intersects(cp->cpus_allowed,
+					 housekeeping_cpumask(HK_FLAG_DOMAIN))))
+			continue;
+
+		if (is_sched_load_balance(cp))
+			csa[csn++] = cp;
+
+		/* skip @cp's subtree */
+		pos_css = css_rightmost_descendant(pos_css);
+	}
+	rcu_read_unlock();
+
+	for (i = 0; i < csn; i++)
+		csa[i]->pn = i;
+	ndoms = csn;
+
+restart:
+	/* Find the best partition (set of sched domains) */
+	for (i = 0; i < csn; i++) {
+		struct cpuset *a = csa[i];
+		int apn = a->pn;
+
+		for (j = 0; j < csn; j++) {
+			struct cpuset *b = csa[j];
+			int bpn = b->pn;
+
+			if (apn != bpn && cpusets_overlap(a, b)) {
+				for (k = 0; k < csn; k++) {
+					struct cpuset *c = csa[k];
+
+					if (c->pn == bpn)
+						c->pn = apn;
+				}
+				ndoms--;	/* one less element */
+				goto restart;
+			}
+		}
+	}
+
+	/*
+	 * Now we know how many domains to create.
+	 * Convert <csn, csa> to <ndoms, doms> and populate cpu masks.
+	 */
+	doms = alloc_sched_domains(ndoms);
+	if (!doms)
+		goto done;
+
+	/*
+	 * The rest of the code, including the scheduler, can deal with
+	 * dattr==NULL case. No need to abort if alloc fails.
+	 */
+	dattr = kmalloc_array(ndoms, sizeof(struct sched_domain_attr),
+			      GFP_KERNEL);
+
+	for (nslot = 0, i = 0; i < csn; i++) {
+		struct cpuset *a = csa[i];
+		struct cpumask *dp;
+		int apn = a->pn;
+
+		if (apn < 0) {
+			/* Skip completed partitions */
+			continue;
+		}
+
+		dp = doms[nslot];
+
+		if (nslot == ndoms) {
+			static int warnings = 10;
+			if (warnings) {
+				pr_warn("rebuild_sched_domains confused: nslot %d, ndoms %d, csn %d, i %d, apn %d\n",
+					nslot, ndoms, csn, i, apn);
+				warnings--;
+			}
+			continue;
+		}
+
+		cpumask_clear(dp);
+		if (dattr)
+			*(dattr + nslot) = SD_ATTR_INIT;
+		for (j = i; j < csn; j++) {
+			struct cpuset *b = csa[j];
+
+			if (apn == b->pn) {
+				cpumask_or(dp, dp, b->effective_cpus);
+				cpumask_and(dp, dp, housekeeping_cpumask(HK_FLAG_DOMAIN));
+				if (dattr)
+					update_domain_attr_tree(dattr + nslot, b);
+
+				/* Done with this partition */
+				b->pn = -1;
+			}
+		}
+		nslot++;
+	}
+	BUG_ON(nslot != ndoms);
+
+done:
+	kfree(csa);
+
+	/*
+	 * Fallback to the default domain if kmalloc() failed.
+	 * See comments in partition_sched_domains().
+	 */
+	if (doms == NULL)
+		ndoms = 1;
+
+	*domains    = doms;
+	*attributes = dattr;
+	return ndoms;
+}
+
+/*
+ * Rebuild scheduler domains.
+ *
+ * If the flag 'sched_load_balance' of any cpuset with non-empty
+ * 'cpus' changes, or if the 'cpus' allowed changes in any cpuset
+ * which has that flag enabled, or if any cpuset with a non-empty
+ * 'cpus' is removed, then call this routine to rebuild the
+ * scheduler's dynamic sched domains.
+ *
+ * Call with cpuset_mutex held.  Takes get_online_cpus().
+ */
+static void rebuild_sched_domains_locked(void)
+{
+	struct sched_domain_attr *attr;
+	cpumask_var_t *doms;
+	int ndoms;
+
+	lockdep_assert_held(&cpuset_mutex);
+	get_online_cpus();
+
+	/*
+	 * We have raced with CPU hotplug. Don't do anything to avoid
+	 * passing doms with offlined cpu to partition_sched_domains().
+	 * Anyways, hotplug work item will rebuild sched domains.
+	 */
+	if (!cpumask_equal(top_cpuset.effective_cpus, cpu_active_mask))
+		goto out;
+
+	/* Generate domain masks and attrs */
+	ndoms = generate_sched_domains(&doms, &attr);
+
+	/* Have scheduler rebuild the domains */
+	partition_sched_domains(ndoms, doms, attr);
+out:
+	put_online_cpus();
+}
+#else /* !CONFIG_SMP */
+static void rebuild_sched_domains_locked(void)
+{
+}
+#endif /* CONFIG_SMP */
+
+void rebuild_sched_domains(void)
+{
+	mutex_lock(&cpuset_mutex);
+	rebuild_sched_domains_locked();
+	mutex_unlock(&cpuset_mutex);
+}
+
+/**
+ * update_tasks_cpumask - Update the cpumasks of tasks in the cpuset.
+ * @cs: the cpuset in which each task's cpus_allowed mask needs to be changed
+ *
+ * Iterate through each task of @cs updating its cpus_allowed to the
+ * effective cpuset's.  As this function is called with cpuset_mutex held,
+ * cpuset membership stays stable.
+ */
+static void update_tasks_cpumask(struct cpuset *cs)
+{
+	struct css_task_iter it;
+	struct task_struct *task;
+
+	css_task_iter_start(&cs->css, 0, &it);
+	while ((task = css_task_iter_next(&it)))
+		set_cpus_allowed_ptr(task, cs->effective_cpus);
+	css_task_iter_end(&it);
+}
+
+/*
+ * update_cpumasks_hier - Update effective cpumasks and tasks in the subtree
+ * @cs: the cpuset to consider
+ * @new_cpus: temp variable for calculating new effective_cpus
+ *
+ * When congifured cpumask is changed, the effective cpumasks of this cpuset
+ * and all its descendants need to be updated.
+ *
+ * On legacy hierachy, effective_cpus will be the same with cpu_allowed.
+ *
+ * Called with cpuset_mutex held
+ */
+static void update_cpumasks_hier(struct cpuset *cs, struct cpumask *new_cpus)
+{
+	struct cpuset *cp;
+	struct cgroup_subsys_state *pos_css;
+	bool need_rebuild_sched_domains = false;
+
+	rcu_read_lock();
+	cpuset_for_each_descendant_pre(cp, pos_css, cs) {
+		struct cpuset *parent = parent_cs(cp);
+
+		cpumask_and(new_cpus, cp->cpus_allowed, parent->effective_cpus);
+
+		/*
+		 * If it becomes empty, inherit the effective mask of the
+		 * parent, which is guaranteed to have some CPUs.
+		 */
+		if (is_in_v2_mode() && cpumask_empty(new_cpus))
+			cpumask_copy(new_cpus, parent->effective_cpus);
+
+		/* Skip the whole subtree if the cpumask remains the same. */
+		if (cpumask_equal(new_cpus, cp->effective_cpus)) {
+			pos_css = css_rightmost_descendant(pos_css);
+			continue;
+		}
+
+		if (!css_tryget_online(&cp->css))
+			continue;
+		rcu_read_unlock();
+
+		spin_lock_irq(&callback_lock);
+		cpumask_copy(cp->effective_cpus, new_cpus);
+		spin_unlock_irq(&callback_lock);
+
+		WARN_ON(!is_in_v2_mode() &&
+			!cpumask_equal(cp->cpus_allowed, cp->effective_cpus));
+
+		update_tasks_cpumask(cp);
+
+		/*
+		 * If the effective cpumask of any non-empty cpuset is changed,
+		 * we need to rebuild sched domains.
+		 */
+		if (!cpumask_empty(cp->cpus_allowed) &&
+		    is_sched_load_balance(cp))
+			need_rebuild_sched_domains = true;
+
+		rcu_read_lock();
+		css_put(&cp->css);
+	}
+	rcu_read_unlock();
+
+	if (need_rebuild_sched_domains)
+		rebuild_sched_domains_locked();
+}
+
+/**
+ * update_cpumask - update the cpus_allowed mask of a cpuset and all tasks in it
+ * @cs: the cpuset to consider
+ * @trialcs: trial cpuset
+ * @buf: buffer of cpu numbers written to this cpuset
+ */
+static int update_cpumask(struct cpuset *cs, struct cpuset *trialcs,
+			  const char *buf)
+{
+	int retval;
+
+	/* top_cpuset.cpus_allowed tracks cpu_online_mask; it's read-only */
+	if (cs == &top_cpuset)
+		return -EACCES;
+
+	/*
+	 * An empty cpus_allowed is ok only if the cpuset has no tasks.
+	 * Since cpulist_parse() fails on an empty mask, we special case
+	 * that parsing.  The validate_change() call ensures that cpusets
+	 * with tasks have cpus.
+	 */
+	if (!*buf) {
+		cpumask_clear(trialcs->cpus_allowed);
+	} else {
+		retval = cpulist_parse(buf, trialcs->cpus_allowed);
+		if (retval < 0)
+			return retval;
+
+		if (!cpumask_subset(trialcs->cpus_allowed,
+				    top_cpuset.cpus_allowed))
+			return -EINVAL;
+	}
+
+	/* Nothing to do if the cpus didn't change */
+	if (cpumask_equal(cs->cpus_allowed, trialcs->cpus_allowed))
+		return 0;
+
+	retval = validate_change(cs, trialcs);
+	if (retval < 0)
+		return retval;
+
+	spin_lock_irq(&callback_lock);
+	cpumask_copy(cs->cpus_allowed, trialcs->cpus_allowed);
+	spin_unlock_irq(&callback_lock);
+
+	/* use trialcs->cpus_allowed as a temp variable */
+	update_cpumasks_hier(cs, trialcs->cpus_allowed);
+	return 0;
+}
+
+/*
+ * Migrate memory region from one set of nodes to another.  This is
+ * performed asynchronously as it can be called from process migration path
+ * holding locks involved in process management.  All mm migrations are
+ * performed in the queued order and can be waited for by flushing
+ * cpuset_migrate_mm_wq.
+ */
+
+struct cpuset_migrate_mm_work {
+	struct work_struct	work;
+	struct mm_struct	*mm;
+	nodemask_t		from;
+	nodemask_t		to;
+};
+
+static void cpuset_migrate_mm_workfn(struct work_struct *work)
+{
+	struct cpuset_migrate_mm_work *mwork =
+		container_of(work, struct cpuset_migrate_mm_work, work);
+
+	/* on a wq worker, no need to worry about %current's mems_allowed */
+	do_migrate_pages(mwork->mm, &mwork->from, &mwork->to, MPOL_MF_MOVE_ALL);
+	mmput(mwork->mm);
+	kfree(mwork);
+}
+
+static void cpuset_migrate_mm(struct mm_struct *mm, const nodemask_t *from,
+							const nodemask_t *to)
+{
+	struct cpuset_migrate_mm_work *mwork;
+
+	mwork = kzalloc(sizeof(*mwork), GFP_KERNEL);
+	if (mwork) {
+		mwork->mm = mm;
+		mwork->from = *from;
+		mwork->to = *to;
+		INIT_WORK(&mwork->work, cpuset_migrate_mm_workfn);
+		queue_work(cpuset_migrate_mm_wq, &mwork->work);
+	} else {
+		mmput(mm);
+	}
+}
+
+static void cpuset_post_attach(void)
+{
+	flush_workqueue(cpuset_migrate_mm_wq);
+}
+
+/*
+ * cpuset_change_task_nodemask - change task's mems_allowed and mempolicy
+ * @tsk: the task to change
+ * @newmems: new nodes that the task will be set
+ *
+ * We use the mems_allowed_seq seqlock to safely update both tsk->mems_allowed
+ * and rebind an eventual tasks' mempolicy. If the task is allocating in
+ * parallel, it might temporarily see an empty intersection, which results in
+ * a seqlock check and retry before OOM or allocation failure.
+ */
+static void cpuset_change_task_nodemask(struct task_struct *tsk,
+					nodemask_t *newmems)
+{
+	task_lock(tsk);
+
+	local_irq_disable();
+	write_seqcount_begin(&tsk->mems_allowed_seq);
+
+	nodes_or(tsk->mems_allowed, tsk->mems_allowed, *newmems);
+	mpol_rebind_task(tsk, newmems);
+	tsk->mems_allowed = *newmems;
+
+	write_seqcount_end(&tsk->mems_allowed_seq);
+	local_irq_enable();
+
+	task_unlock(tsk);
+}
+
+static void *cpuset_being_rebound;
+
+/**
+ * update_tasks_nodemask - Update the nodemasks of tasks in the cpuset.
+ * @cs: the cpuset in which each task's mems_allowed mask needs to be changed
+ *
+ * Iterate through each task of @cs updating its mems_allowed to the
+ * effective cpuset's.  As this function is called with cpuset_mutex held,
+ * cpuset membership stays stable.
+ */
+static void update_tasks_nodemask(struct cpuset *cs)
+{
+	static nodemask_t newmems;	/* protected by cpuset_mutex */
+	struct css_task_iter it;
+	struct task_struct *task;
+
+	cpuset_being_rebound = cs;		/* causes mpol_dup() rebind */
+
+	guarantee_online_mems(cs, &newmems);
+
+	/*
+	 * The mpol_rebind_mm() call takes mmap_sem, which we couldn't
+	 * take while holding tasklist_lock.  Forks can happen - the
+	 * mpol_dup() cpuset_being_rebound check will catch such forks,
+	 * and rebind their vma mempolicies too.  Because we still hold
+	 * the global cpuset_mutex, we know that no other rebind effort
+	 * will be contending for the global variable cpuset_being_rebound.
+	 * It's ok if we rebind the same mm twice; mpol_rebind_mm()
+	 * is idempotent.  Also migrate pages in each mm to new nodes.
+	 */
+	css_task_iter_start(&cs->css, 0, &it);
+	while ((task = css_task_iter_next(&it))) {
+		struct mm_struct *mm;
+		bool migrate;
+
+		cpuset_change_task_nodemask(task, &newmems);
+
+		mm = get_task_mm(task);
+		if (!mm)
+			continue;
+
+		migrate = is_memory_migrate(cs);
+
+		mpol_rebind_mm(mm, &cs->mems_allowed);
+		if (migrate)
+			cpuset_migrate_mm(mm, &cs->old_mems_allowed, &newmems);
+		else
+			mmput(mm);
+	}
+	css_task_iter_end(&it);
+
+	/*
+	 * All the tasks' nodemasks have been updated, update
+	 * cs->old_mems_allowed.
+	 */
+	cs->old_mems_allowed = newmems;
+
+	/* We're done rebinding vmas to this cpuset's new mems_allowed. */
+	cpuset_being_rebound = NULL;
+}
+
+/*
+ * update_nodemasks_hier - Update effective nodemasks and tasks in the subtree
+ * @cs: the cpuset to consider
+ * @new_mems: a temp variable for calculating new effective_mems
+ *
+ * When configured nodemask is changed, the effective nodemasks of this cpuset
+ * and all its descendants need to be updated.
+ *
+ * On legacy hiearchy, effective_mems will be the same with mems_allowed.
+ *
+ * Called with cpuset_mutex held
+ */
+static void update_nodemasks_hier(struct cpuset *cs, nodemask_t *new_mems)
+{
+	struct cpuset *cp;
+	struct cgroup_subsys_state *pos_css;
+
+	rcu_read_lock();
+	cpuset_for_each_descendant_pre(cp, pos_css, cs) {
+		struct cpuset *parent = parent_cs(cp);
+
+		nodes_and(*new_mems, cp->mems_allowed, parent->effective_mems);
+
+		/*
+		 * If it becomes empty, inherit the effective mask of the
+		 * parent, which is guaranteed to have some MEMs.
+		 */
+		if (is_in_v2_mode() && nodes_empty(*new_mems))
+			*new_mems = parent->effective_mems;
+
+		/* Skip the whole subtree if the nodemask remains the same. */
+		if (nodes_equal(*new_mems, cp->effective_mems)) {
+			pos_css = css_rightmost_descendant(pos_css);
+			continue;
+		}
+
+		if (!css_tryget_online(&cp->css))
+			continue;
+		rcu_read_unlock();
+
+		spin_lock_irq(&callback_lock);
+		cp->effective_mems = *new_mems;
+		spin_unlock_irq(&callback_lock);
+
+		WARN_ON(!is_in_v2_mode() &&
+			!nodes_equal(cp->mems_allowed, cp->effective_mems));
+
+		update_tasks_nodemask(cp);
+
+		rcu_read_lock();
+		css_put(&cp->css);
+	}
+	rcu_read_unlock();
+}
+
+/*
+ * Handle user request to change the 'mems' memory placement
+ * of a cpuset.  Needs to validate the request, update the
+ * cpusets mems_allowed, and for each task in the cpuset,
+ * update mems_allowed and rebind task's mempolicy and any vma
+ * mempolicies and if the cpuset is marked 'memory_migrate',
+ * migrate the tasks pages to the new memory.
+ *
+ * Call with cpuset_mutex held. May take callback_lock during call.
+ * Will take tasklist_lock, scan tasklist for tasks in cpuset cs,
+ * lock each such tasks mm->mmap_sem, scan its vma's and rebind
+ * their mempolicies to the cpusets new mems_allowed.
+ */
+static int update_nodemask(struct cpuset *cs, struct cpuset *trialcs,
+			   const char *buf)
+{
+	int retval;
+
+	/*
+	 * top_cpuset.mems_allowed tracks node_stats[N_MEMORY];
+	 * it's read-only
+	 */
+	if (cs == &top_cpuset) {
+		retval = -EACCES;
+		goto done;
+	}
+
+	/*
+	 * An empty mems_allowed is ok iff there are no tasks in the cpuset.
+	 * Since nodelist_parse() fails on an empty mask, we special case
+	 * that parsing.  The validate_change() call ensures that cpusets
+	 * with tasks have memory.
+	 */
+	if (!*buf) {
+		nodes_clear(trialcs->mems_allowed);
+	} else {
+		retval = nodelist_parse(buf, trialcs->mems_allowed);
+		if (retval < 0)
+			goto done;
+
+		if (!nodes_subset(trialcs->mems_allowed,
+				  top_cpuset.mems_allowed)) {
+			retval = -EINVAL;
+			goto done;
+		}
+	}
+
+	if (nodes_equal(cs->mems_allowed, trialcs->mems_allowed)) {
+		retval = 0;		/* Too easy - nothing to do */
+		goto done;
+	}
+	retval = validate_change(cs, trialcs);
+	if (retval < 0)
+		goto done;
+
+	spin_lock_irq(&callback_lock);
+	cs->mems_allowed = trialcs->mems_allowed;
+	spin_unlock_irq(&callback_lock);
+
+	/* use trialcs->mems_allowed as a temp variable */
+	update_nodemasks_hier(cs, &trialcs->mems_allowed);
+done:
+	return retval;
+}
+
+bool current_cpuset_is_being_rebound(void)
+{
+	bool ret;
+
+	rcu_read_lock();
+	ret = task_cs(current) == cpuset_being_rebound;
+	rcu_read_unlock();
+
+	return ret;
+}
+
+static int update_relax_domain_level(struct cpuset *cs, s64 val)
+{
+#ifdef CONFIG_SMP
+	if (val < -1 || val >= sched_domain_level_max)
+		return -EINVAL;
+#endif
+
+	if (val != cs->relax_domain_level) {
+		cs->relax_domain_level = val;
+		if (!cpumask_empty(cs->cpus_allowed) &&
+		    is_sched_load_balance(cs))
+			rebuild_sched_domains_locked();
+	}
+
+	return 0;
+}
+
+/**
+ * update_tasks_flags - update the spread flags of tasks in the cpuset.
+ * @cs: the cpuset in which each task's spread flags needs to be changed
+ *
+ * Iterate through each task of @cs updating its spread flags.  As this
+ * function is called with cpuset_mutex held, cpuset membership stays
+ * stable.
+ */
+static void update_tasks_flags(struct cpuset *cs)
+{
+	struct css_task_iter it;
+	struct task_struct *task;
+
+	css_task_iter_start(&cs->css, 0, &it);
+	while ((task = css_task_iter_next(&it)))
+		cpuset_update_task_spread_flag(cs, task);
+	css_task_iter_end(&it);
+}
+
+/*
+ * update_flag - read a 0 or a 1 in a file and update associated flag
+ * bit:		the bit to update (see cpuset_flagbits_t)
+ * cs:		the cpuset to update
+ * turning_on: 	whether the flag is being set or cleared
+ *
+ * Call with cpuset_mutex held.
+ */
+
+static int update_flag(cpuset_flagbits_t bit, struct cpuset *cs,
+		       int turning_on)
+{
+	struct cpuset *trialcs;
+	int balance_flag_changed;
+	int spread_flag_changed;
+	int err;
+
+	trialcs = alloc_trial_cpuset(cs);
+	if (!trialcs)
+		return -ENOMEM;
+
+	if (turning_on)
+		set_bit(bit, &trialcs->flags);
+	else
+		clear_bit(bit, &trialcs->flags);
+
+	err = validate_change(cs, trialcs);
+	if (err < 0)
+		goto out;
+
+	balance_flag_changed = (is_sched_load_balance(cs) !=
+				is_sched_load_balance(trialcs));
+
+	spread_flag_changed = ((is_spread_slab(cs) != is_spread_slab(trialcs))
+			|| (is_spread_page(cs) != is_spread_page(trialcs)));
+
+	spin_lock_irq(&callback_lock);
+	cs->flags = trialcs->flags;
+	spin_unlock_irq(&callback_lock);
+
+	if (!cpumask_empty(trialcs->cpus_allowed) && balance_flag_changed)
+		rebuild_sched_domains_locked();
+
+	if (spread_flag_changed)
+		update_tasks_flags(cs);
+out:
+	free_trial_cpuset(trialcs);
+	return err;
+}
+
+/*
+ * Frequency meter - How fast is some event occurring?
+ *
+ * These routines manage a digitally filtered, constant time based,
+ * event frequency meter.  There are four routines:
+ *   fmeter_init() - initialize a frequency meter.
+ *   fmeter_markevent() - called each time the event happens.
+ *   fmeter_getrate() - returns the recent rate of such events.
+ *   fmeter_update() - internal routine used to update fmeter.
+ *
+ * A common data structure is passed to each of these routines,
+ * which is used to keep track of the state required to manage the
+ * frequency meter and its digital filter.
+ *
+ * The filter works on the number of events marked per unit time.
+ * The filter is single-pole low-pass recursive (IIR).  The time unit
+ * is 1 second.  Arithmetic is done using 32-bit integers scaled to
+ * simulate 3 decimal digits of precision (multiplied by 1000).
+ *
+ * With an FM_COEF of 933, and a time base of 1 second, the filter
+ * has a half-life of 10 seconds, meaning that if the events quit
+ * happening, then the rate returned from the fmeter_getrate()
+ * will be cut in half each 10 seconds, until it converges to zero.
+ *
+ * It is not worth doing a real infinitely recursive filter.  If more
+ * than FM_MAXTICKS ticks have elapsed since the last filter event,
+ * just compute FM_MAXTICKS ticks worth, by which point the level
+ * will be stable.
+ *
+ * Limit the count of unprocessed events to FM_MAXCNT, so as to avoid
+ * arithmetic overflow in the fmeter_update() routine.
+ *
+ * Given the simple 32 bit integer arithmetic used, this meter works
+ * best for reporting rates between one per millisecond (msec) and
+ * one per 32 (approx) seconds.  At constant rates faster than one
+ * per msec it maxes out at values just under 1,000,000.  At constant
+ * rates between one per msec, and one per second it will stabilize
+ * to a value N*1000, where N is the rate of events per second.
+ * At constant rates between one per second and one per 32 seconds,
+ * it will be choppy, moving up on the seconds that have an event,
+ * and then decaying until the next event.  At rates slower than
+ * about one in 32 seconds, it decays all the way back to zero between
+ * each event.
+ */
+
+#define FM_COEF 933		/* coefficient for half-life of 10 secs */
+#define FM_MAXTICKS ((u32)99)   /* useless computing more ticks than this */
+#define FM_MAXCNT 1000000	/* limit cnt to avoid overflow */
+#define FM_SCALE 1000		/* faux fixed point scale */
+
+/* Initialize a frequency meter */
+static void fmeter_init(struct fmeter *fmp)
+{
+	fmp->cnt = 0;
+	fmp->val = 0;
+	fmp->time = 0;
+	spin_lock_init(&fmp->lock);
+}
+
+/* Internal meter update - process cnt events and update value */
+static void fmeter_update(struct fmeter *fmp)
+{
+	time64_t now;
+	u32 ticks;
+
+	now = ktime_get_seconds();
+	ticks = now - fmp->time;
+
+	if (ticks == 0)
+		return;
+
+	ticks = min(FM_MAXTICKS, ticks);
+	while (ticks-- > 0)
+		fmp->val = (FM_COEF * fmp->val) / FM_SCALE;
+	fmp->time = now;
+
+	fmp->val += ((FM_SCALE - FM_COEF) * fmp->cnt) / FM_SCALE;
+	fmp->cnt = 0;
+}
+
+/* Process any previous ticks, then bump cnt by one (times scale). */
+static void fmeter_markevent(struct fmeter *fmp)
+{
+	spin_lock(&fmp->lock);
+	fmeter_update(fmp);
+	fmp->cnt = min(FM_MAXCNT, fmp->cnt + FM_SCALE);
+	spin_unlock(&fmp->lock);
+}
+
+/* Process any previous ticks, then return current value. */
+static int fmeter_getrate(struct fmeter *fmp)
+{
+	int val;
+
+	spin_lock(&fmp->lock);
+	fmeter_update(fmp);
+	val = fmp->val;
+	spin_unlock(&fmp->lock);
+	return val;
+}
+
+static struct cpuset *cpuset_attach_old_cs;
+
+/* Called by cgroups to determine if a cpuset is usable; cpuset_mutex held */
+static int cpuset_can_attach(struct cgroup_taskset *tset)
+{
+	struct cgroup_subsys_state *css;
+	struct cpuset *cs;
+	struct task_struct *task;
+	int ret;
+
+	/* used later by cpuset_attach() */
+	cpuset_attach_old_cs = task_cs(cgroup_taskset_first(tset, &css));
+	cs = css_cs(css);
+
+	mutex_lock(&cpuset_mutex);
+
+	/* allow moving tasks into an empty cpuset if on default hierarchy */
+	ret = -ENOSPC;
+	if (!is_in_v2_mode() &&
+	    (cpumask_empty(cs->cpus_allowed) || nodes_empty(cs->mems_allowed)))
+		goto out_unlock;
+
+	cgroup_taskset_for_each(task, css, tset) {
+		ret = task_can_attach(task, cs->cpus_allowed);
+		if (ret)
+			goto out_unlock;
+		ret = security_task_setscheduler(task);
+		if (ret)
+			goto out_unlock;
+	}
+
+	/*
+	 * Mark attach is in progress.  This makes validate_change() fail
+	 * changes which zero cpus/mems_allowed.
+	 */
+	cs->attach_in_progress++;
+	ret = 0;
+out_unlock:
+	mutex_unlock(&cpuset_mutex);
+	return ret;
+}
+
+static void cpuset_cancel_attach(struct cgroup_taskset *tset)
+{
+	struct cgroup_subsys_state *css;
+	struct cpuset *cs;
+
+	cgroup_taskset_first(tset, &css);
+	cs = css_cs(css);
+
+	mutex_lock(&cpuset_mutex);
+	css_cs(css)->attach_in_progress--;
+	mutex_unlock(&cpuset_mutex);
+}
+
+/*
+ * Protected by cpuset_mutex.  cpus_attach is used only by cpuset_attach()
+ * but we can't allocate it dynamically there.  Define it global and
+ * allocate from cpuset_init().
+ */
+static cpumask_var_t cpus_attach;
+
+static void cpuset_attach(struct cgroup_taskset *tset)
+{
+	/* static buf protected by cpuset_mutex */
+	static nodemask_t cpuset_attach_nodemask_to;
+	struct task_struct *task;
+	struct task_struct *leader;
+	struct cgroup_subsys_state *css;
+	struct cpuset *cs;
+	struct cpuset *oldcs = cpuset_attach_old_cs;
+
+	cgroup_taskset_first(tset, &css);
+	cs = css_cs(css);
+
+	mutex_lock(&cpuset_mutex);
+
+	/*
+	 * It should hold cpus lock because a cpu offline event can
+	 * cause set_cpus_allowed_ptr() failed.
+	 */
+	get_online_cpus();
+	/* prepare for attach */
+	if (cs == &top_cpuset)
+		cpumask_copy(cpus_attach, cpu_possible_mask);
+	else
+		guarantee_online_cpus(cs, cpus_attach);
+
+	guarantee_online_mems(cs, &cpuset_attach_nodemask_to);
+
+	cgroup_taskset_for_each(task, css, tset) {
+		/*
+		 * can_attach beforehand should guarantee that this doesn't
+		 * fail.  TODO: have a better way to handle failure here
+		 */
+		WARN_ON_ONCE(set_cpus_allowed_ptr(task, cpus_attach));
+
+		cpuset_change_task_nodemask(task, &cpuset_attach_nodemask_to);
+		cpuset_update_task_spread_flag(cs, task);
+	}
+       put_online_cpus();
+
+	/*
+	 * Change mm for all threadgroup leaders. This is expensive and may
+	 * sleep and should be moved outside migration path proper.
+	 */
+	cpuset_attach_nodemask_to = cs->effective_mems;
+	cgroup_taskset_for_each_leader(leader, css, tset) {
+		struct mm_struct *mm = get_task_mm(leader);
+
+		if (mm) {
+			mpol_rebind_mm(mm, &cpuset_attach_nodemask_to);
+
+			/*
+			 * old_mems_allowed is the same with mems_allowed
+			 * here, except if this task is being moved
+			 * automatically due to hotplug.  In that case
+			 * @mems_allowed has been updated and is empty, so
+			 * @old_mems_allowed is the right nodesets that we
+			 * migrate mm from.
+			 */
+			if (is_memory_migrate(cs))
+				cpuset_migrate_mm(mm, &oldcs->old_mems_allowed,
+						  &cpuset_attach_nodemask_to);
+			else
+				mmput(mm);
+		}
+	}
+
+	cs->old_mems_allowed = cpuset_attach_nodemask_to;
+
+	cs->attach_in_progress--;
+	if (!cs->attach_in_progress)
+		wake_up(&cpuset_attach_wq);
+
+	mutex_unlock(&cpuset_mutex);
+}
+
+/* The various types of files and directories in a cpuset file system */
+
+typedef enum {
+	FILE_MEMORY_MIGRATE,
+	FILE_CPULIST,
+	FILE_MEMLIST,
+	FILE_EFFECTIVE_CPULIST,
+	FILE_EFFECTIVE_MEMLIST,
+	FILE_CPU_EXCLUSIVE,
+	FILE_MEM_EXCLUSIVE,
+	FILE_MEM_HARDWALL,
+	FILE_SCHED_LOAD_BALANCE,
+	FILE_SCHED_RELAX_DOMAIN_LEVEL,
+	FILE_MEMORY_PRESSURE_ENABLED,
+	FILE_MEMORY_PRESSURE,
+	FILE_SPREAD_PAGE,
+	FILE_SPREAD_SLAB,
+} cpuset_filetype_t;
+
+static int cpuset_write_u64(struct cgroup_subsys_state *css, struct cftype *cft,
+			    u64 val)
+{
+	struct cpuset *cs = css_cs(css);
+	cpuset_filetype_t type = cft->private;
+	int retval = 0;
+
+	mutex_lock(&cpuset_mutex);
+	if (!is_cpuset_online(cs)) {
+		retval = -ENODEV;
+		goto out_unlock;
+	}
+
+	switch (type) {
+	case FILE_CPU_EXCLUSIVE:
+		retval = update_flag(CS_CPU_EXCLUSIVE, cs, val);
+		break;
+	case FILE_MEM_EXCLUSIVE:
+		retval = update_flag(CS_MEM_EXCLUSIVE, cs, val);
+		break;
+	case FILE_MEM_HARDWALL:
+		retval = update_flag(CS_MEM_HARDWALL, cs, val);
+		break;
+	case FILE_SCHED_LOAD_BALANCE:
+		retval = update_flag(CS_SCHED_LOAD_BALANCE, cs, val);
+		break;
+	case FILE_MEMORY_MIGRATE:
+		retval = update_flag(CS_MEMORY_MIGRATE, cs, val);
+		break;
+	case FILE_MEMORY_PRESSURE_ENABLED:
+		cpuset_memory_pressure_enabled = !!val;
+		break;
+	case FILE_SPREAD_PAGE:
+		retval = update_flag(CS_SPREAD_PAGE, cs, val);
+		break;
+	case FILE_SPREAD_SLAB:
+		retval = update_flag(CS_SPREAD_SLAB, cs, val);
+		break;
+	default:
+		retval = -EINVAL;
+		break;
+	}
+out_unlock:
+	mutex_unlock(&cpuset_mutex);
+	return retval;
+}
+
+static int cpuset_write_s64(struct cgroup_subsys_state *css, struct cftype *cft,
+			    s64 val)
+{
+	struct cpuset *cs = css_cs(css);
+	cpuset_filetype_t type = cft->private;
+	int retval = -ENODEV;
+
+	mutex_lock(&cpuset_mutex);
+	if (!is_cpuset_online(cs))
+		goto out_unlock;
+
+	switch (type) {
+	case FILE_SCHED_RELAX_DOMAIN_LEVEL:
+		retval = update_relax_domain_level(cs, val);
+		break;
+	default:
+		retval = -EINVAL;
+		break;
+	}
+out_unlock:
+	mutex_unlock(&cpuset_mutex);
+	return retval;
+}
+
+/*
+ * Common handling for a write to a "cpus" or "mems" file.
+ */
+static ssize_t cpuset_write_resmask(struct kernfs_open_file *of,
+				    char *buf, size_t nbytes, loff_t off)
+{
+	struct cpuset *cs = css_cs(of_css(of));
+	struct cpuset *trialcs;
+	int retval = -ENODEV;
+
+	buf = strstrip(buf);
+
+	/*
+	 * CPU or memory hotunplug may leave @cs w/o any execution
+	 * resources, in which case the hotplug code asynchronously updates
+	 * configuration and transfers all tasks to the nearest ancestor
+	 * which can execute.
+	 *
+	 * As writes to "cpus" or "mems" may restore @cs's execution
+	 * resources, wait for the previously scheduled operations before
+	 * proceeding, so that we don't end up keep removing tasks added
+	 * after execution capability is restored.
+	 *
+	 * cpuset_hotplug_work calls back into cgroup core via
+	 * cgroup_transfer_tasks() and waiting for it from a cgroupfs
+	 * operation like this one can lead to a deadlock through kernfs
+	 * active_ref protection.  Let's break the protection.  Losing the
+	 * protection is okay as we check whether @cs is online after
+	 * grabbing cpuset_mutex anyway.  This only happens on the legacy
+	 * hierarchies.
+	 */
+	css_get(&cs->css);
+	kernfs_break_active_protection(of->kn);
+	flush_work(&cpuset_hotplug_work);
+
+	mutex_lock(&cpuset_mutex);
+	if (!is_cpuset_online(cs))
+		goto out_unlock;
+
+	trialcs = alloc_trial_cpuset(cs);
+	if (!trialcs) {
+		retval = -ENOMEM;
+		goto out_unlock;
+	}
+
+	switch (of_cft(of)->private) {
+	case FILE_CPULIST:
+		retval = update_cpumask(cs, trialcs, buf);
+		break;
+	case FILE_MEMLIST:
+		retval = update_nodemask(cs, trialcs, buf);
+		break;
+	default:
+		retval = -EINVAL;
+		break;
+	}
+
+	free_trial_cpuset(trialcs);
+out_unlock:
+	mutex_unlock(&cpuset_mutex);
+	kernfs_unbreak_active_protection(of->kn);
+	css_put(&cs->css);
+	flush_workqueue(cpuset_migrate_mm_wq);
+	return retval ?: nbytes;
+}
+
+/*
+ * These ascii lists should be read in a single call, by using a user
+ * buffer large enough to hold the entire map.  If read in smaller
+ * chunks, there is no guarantee of atomicity.  Since the display format
+ * used, list of ranges of sequential numbers, is variable length,
+ * and since these maps can change value dynamically, one could read
+ * gibberish by doing partial reads while a list was changing.
+ */
+static int cpuset_common_seq_show(struct seq_file *sf, void *v)
+{
+	struct cpuset *cs = css_cs(seq_css(sf));
+	cpuset_filetype_t type = seq_cft(sf)->private;
+	int ret = 0;
+
+	spin_lock_irq(&callback_lock);
+
+	switch (type) {
+	case FILE_CPULIST:
+		seq_printf(sf, "%*pbl\n", cpumask_pr_args(cs->cpus_allowed));
+		break;
+	case FILE_MEMLIST:
+		seq_printf(sf, "%*pbl\n", nodemask_pr_args(&cs->mems_allowed));
+		break;
+	case FILE_EFFECTIVE_CPULIST:
+		seq_printf(sf, "%*pbl\n", cpumask_pr_args(cs->effective_cpus));
+		break;
+	case FILE_EFFECTIVE_MEMLIST:
+		seq_printf(sf, "%*pbl\n", nodemask_pr_args(&cs->effective_mems));
+		break;
+	default:
+		ret = -EINVAL;
+	}
+
+	spin_unlock_irq(&callback_lock);
+	return ret;
+}
+
+static u64 cpuset_read_u64(struct cgroup_subsys_state *css, struct cftype *cft)
+{
+	struct cpuset *cs = css_cs(css);
+	cpuset_filetype_t type = cft->private;
+	switch (type) {
+	case FILE_CPU_EXCLUSIVE:
+		return is_cpu_exclusive(cs);
+	case FILE_MEM_EXCLUSIVE:
+		return is_mem_exclusive(cs);
+	case FILE_MEM_HARDWALL:
+		return is_mem_hardwall(cs);
+	case FILE_SCHED_LOAD_BALANCE:
+		return is_sched_load_balance(cs);
+	case FILE_MEMORY_MIGRATE:
+		return is_memory_migrate(cs);
+	case FILE_MEMORY_PRESSURE_ENABLED:
+		return cpuset_memory_pressure_enabled;
+	case FILE_MEMORY_PRESSURE:
+		return fmeter_getrate(&cs->fmeter);
+	case FILE_SPREAD_PAGE:
+		return is_spread_page(cs);
+	case FILE_SPREAD_SLAB:
+		return is_spread_slab(cs);
+	default:
+		BUG();
+	}
+
+	/* Unreachable but makes gcc happy */
+	return 0;
+}
+
+static s64 cpuset_read_s64(struct cgroup_subsys_state *css, struct cftype *cft)
+{
+	struct cpuset *cs = css_cs(css);
+	cpuset_filetype_t type = cft->private;
+	switch (type) {
+	case FILE_SCHED_RELAX_DOMAIN_LEVEL:
+		return cs->relax_domain_level;
+	default:
+		BUG();
+	}
+
+	/* Unrechable but makes gcc happy */
+	return 0;
+}
+
+
+/*
+ * for the common functions, 'private' gives the type of file
+ */
+
+static struct cftype files[] = {
+	{
+		.name = "cpus",
+		.seq_show = cpuset_common_seq_show,
+		.write = cpuset_write_resmask,
+		.max_write_len = (100U + 6 * NR_CPUS),
+		.private = FILE_CPULIST,
+	},
+
+	{
+		.name = "mems",
+		.seq_show = cpuset_common_seq_show,
+		.write = cpuset_write_resmask,
+		.max_write_len = (100U + 6 * MAX_NUMNODES),
+		.private = FILE_MEMLIST,
+	},
+
+	{
+		.name = "effective_cpus",
+		.seq_show = cpuset_common_seq_show,
+		.private = FILE_EFFECTIVE_CPULIST,
+	},
+
+	{
+		.name = "effective_mems",
+		.seq_show = cpuset_common_seq_show,
+		.private = FILE_EFFECTIVE_MEMLIST,
+	},
+
+	{
+		.name = "cpu_exclusive",
+		.read_u64 = cpuset_read_u64,
+		.write_u64 = cpuset_write_u64,
+		.private = FILE_CPU_EXCLUSIVE,
+	},
+
+	{
+		.name = "mem_exclusive",
+		.read_u64 = cpuset_read_u64,
+		.write_u64 = cpuset_write_u64,
+		.private = FILE_MEM_EXCLUSIVE,
+	},
+
+	{
+		.name = "mem_hardwall",
+		.read_u64 = cpuset_read_u64,
+		.write_u64 = cpuset_write_u64,
+		.private = FILE_MEM_HARDWALL,
+	},
+
+	{
+		.name = "sched_load_balance",
+		.read_u64 = cpuset_read_u64,
+		.write_u64 = cpuset_write_u64,
+		.private = FILE_SCHED_LOAD_BALANCE,
+	},
+
+	{
+		.name = "sched_relax_domain_level",
+		.read_s64 = cpuset_read_s64,
+		.write_s64 = cpuset_write_s64,
+		.private = FILE_SCHED_RELAX_DOMAIN_LEVEL,
+	},
+
+	{
+		.name = "memory_migrate",
+		.read_u64 = cpuset_read_u64,
+		.write_u64 = cpuset_write_u64,
+		.private = FILE_MEMORY_MIGRATE,
+	},
+
+	{
+		.name = "memory_pressure",
+		.read_u64 = cpuset_read_u64,
+		.private = FILE_MEMORY_PRESSURE,
+	},
+
+	{
+		.name = "memory_spread_page",
+		.read_u64 = cpuset_read_u64,
+		.write_u64 = cpuset_write_u64,
+		.private = FILE_SPREAD_PAGE,
+	},
+
+	{
+		.name = "memory_spread_slab",
+		.read_u64 = cpuset_read_u64,
+		.write_u64 = cpuset_write_u64,
+		.private = FILE_SPREAD_SLAB,
+	},
+
+	{
+		.name = "memory_pressure_enabled",
+		.flags = CFTYPE_ONLY_ON_ROOT,
+		.read_u64 = cpuset_read_u64,
+		.write_u64 = cpuset_write_u64,
+		.private = FILE_MEMORY_PRESSURE_ENABLED,
+	},
+
+	{ }	/* terminate */
+};
+
+/*
+ *	cpuset_css_alloc - allocate a cpuset css
+ *	cgrp:	control group that the new cpuset will be part of
+ */
+
+static struct cgroup_subsys_state *
+cpuset_css_alloc(struct cgroup_subsys_state *parent_css)
+{
+	struct cpuset *cs;
+
+	if (!parent_css)
+		return &top_cpuset.css;
+
+	cs = kzalloc(sizeof(*cs), GFP_KERNEL);
+	if (!cs)
+		return ERR_PTR(-ENOMEM);
+	if (!alloc_cpumask_var(&cs->cpus_allowed, GFP_KERNEL))
+		goto free_cs;
+	if (!alloc_cpumask_var(&cs->effective_cpus, GFP_KERNEL))
+		goto free_cpus;
+
+	set_bit(CS_SCHED_LOAD_BALANCE, &cs->flags);
+	cpumask_clear(cs->cpus_allowed);
+	nodes_clear(cs->mems_allowed);
+	cpumask_clear(cs->effective_cpus);
+	nodes_clear(cs->effective_mems);
+	fmeter_init(&cs->fmeter);
+	cs->relax_domain_level = -1;
+
+	return &cs->css;
+
+free_cpus:
+	free_cpumask_var(cs->cpus_allowed);
+free_cs:
+	kfree(cs);
+	return ERR_PTR(-ENOMEM);
+}
+
+static int cpuset_css_online(struct cgroup_subsys_state *css)
+{
+	struct cpuset *cs = css_cs(css);
+	struct cpuset *parent = parent_cs(cs);
+	struct cpuset *tmp_cs;
+	struct cgroup_subsys_state *pos_css;
+
+	if (!parent)
+		return 0;
+
+	mutex_lock(&cpuset_mutex);
+
+	set_bit(CS_ONLINE, &cs->flags);
+	if (is_spread_page(parent))
+		set_bit(CS_SPREAD_PAGE, &cs->flags);
+	if (is_spread_slab(parent))
+		set_bit(CS_SPREAD_SLAB, &cs->flags);
+
+	cpuset_inc();
+
+	spin_lock_irq(&callback_lock);
+	if (is_in_v2_mode()) {
+		cpumask_copy(cs->effective_cpus, parent->effective_cpus);
+		cs->effective_mems = parent->effective_mems;
+	}
+	spin_unlock_irq(&callback_lock);
+
+	if (!test_bit(CGRP_CPUSET_CLONE_CHILDREN, &css->cgroup->flags))
+		goto out_unlock;
+
+	/*
+	 * Clone @parent's configuration if CGRP_CPUSET_CLONE_CHILDREN is
+	 * set.  This flag handling is implemented in cgroup core for
+	 * histrical reasons - the flag may be specified during mount.
+	 *
+	 * Currently, if any sibling cpusets have exclusive cpus or mem, we
+	 * refuse to clone the configuration - thereby refusing the task to
+	 * be entered, and as a result refusing the sys_unshare() or
+	 * clone() which initiated it.  If this becomes a problem for some
+	 * users who wish to allow that scenario, then this could be
+	 * changed to grant parent->cpus_allowed-sibling_cpus_exclusive
+	 * (and likewise for mems) to the new cgroup.
+	 */
+	rcu_read_lock();
+	cpuset_for_each_child(tmp_cs, pos_css, parent) {
+		if (is_mem_exclusive(tmp_cs) || is_cpu_exclusive(tmp_cs)) {
+			rcu_read_unlock();
+			goto out_unlock;
+		}
+	}
+	rcu_read_unlock();
+
+	spin_lock_irq(&callback_lock);
+	cs->mems_allowed = parent->mems_allowed;
+	cs->effective_mems = parent->mems_allowed;
+	cpumask_copy(cs->cpus_allowed, parent->cpus_allowed);
+	cpumask_copy(cs->effective_cpus, parent->cpus_allowed);
+	spin_unlock_irq(&callback_lock);
+out_unlock:
+	mutex_unlock(&cpuset_mutex);
+	return 0;
+}
+
+/*
+ * If the cpuset being removed has its flag 'sched_load_balance'
+ * enabled, then simulate turning sched_load_balance off, which
+ * will call rebuild_sched_domains_locked().
+ */
+
+static void cpuset_css_offline(struct cgroup_subsys_state *css)
+{
+	struct cpuset *cs = css_cs(css);
+
+	mutex_lock(&cpuset_mutex);
+
+	if (is_sched_load_balance(cs))
+		update_flag(CS_SCHED_LOAD_BALANCE, cs, 0);
+
+	cpuset_dec();
+	clear_bit(CS_ONLINE, &cs->flags);
+
+	mutex_unlock(&cpuset_mutex);
+}
+
+static void cpuset_css_free(struct cgroup_subsys_state *css)
+{
+	struct cpuset *cs = css_cs(css);
+
+	free_cpumask_var(cs->effective_cpus);
+	free_cpumask_var(cs->cpus_allowed);
+	kfree(cs);
+}
+
+static void cpuset_bind(struct cgroup_subsys_state *root_css)
+{
+	mutex_lock(&cpuset_mutex);
+	spin_lock_irq(&callback_lock);
+
+	if (is_in_v2_mode()) {
+		cpumask_copy(top_cpuset.cpus_allowed, cpu_possible_mask);
+		top_cpuset.mems_allowed = node_possible_map;
+	} else {
+		cpumask_copy(top_cpuset.cpus_allowed,
+			     top_cpuset.effective_cpus);
+		top_cpuset.mems_allowed = top_cpuset.effective_mems;
+	}
+
+	spin_unlock_irq(&callback_lock);
+	mutex_unlock(&cpuset_mutex);
+}
+
+/*
+ * Make sure the new task conform to the current state of its parent,
+ * which could have been changed by cpuset just after it inherits the
+ * state from the parent and before it sits on the cgroup's task list.
+ */
+static void cpuset_fork(struct task_struct *task)
+{
+	if (task_css_is_root(task, cpuset_cgrp_id))
+		return;
+
+	set_cpus_allowed_ptr(task, &current->cpus_allowed);
+	task->mems_allowed = current->mems_allowed;
+}
+
+struct cgroup_subsys cpuset_cgrp_subsys = {
+	.css_alloc	= cpuset_css_alloc,
+	.css_online	= cpuset_css_online,
+	.css_offline	= cpuset_css_offline,
+	.css_free	= cpuset_css_free,
+	.can_attach	= cpuset_can_attach,
+	.cancel_attach	= cpuset_cancel_attach,
+	.attach		= cpuset_attach,
+	.post_attach	= cpuset_post_attach,
+	.bind		= cpuset_bind,
+	.fork		= cpuset_fork,
+	.legacy_cftypes	= files,
+	.early_init	= true,
+};
+
+/**
+ * cpuset_init - initialize cpusets at system boot
+ *
+ * Description: Initialize top_cpuset and the cpuset internal file system,
+ **/
+
+int __init cpuset_init(void)
+{
+	int err = 0;
+
+	BUG_ON(!alloc_cpumask_var(&top_cpuset.cpus_allowed, GFP_KERNEL));
+	BUG_ON(!alloc_cpumask_var(&top_cpuset.effective_cpus, GFP_KERNEL));
+
+	cpumask_setall(top_cpuset.cpus_allowed);
+	nodes_setall(top_cpuset.mems_allowed);
+	cpumask_setall(top_cpuset.effective_cpus);
+	nodes_setall(top_cpuset.effective_mems);
+
+	fmeter_init(&top_cpuset.fmeter);
+	set_bit(CS_SCHED_LOAD_BALANCE, &top_cpuset.flags);
+	top_cpuset.relax_domain_level = -1;
+
+	err = register_filesystem(&cpuset_fs_type);
+	if (err < 0)
+		return err;
+
+	BUG_ON(!alloc_cpumask_var(&cpus_attach, GFP_KERNEL));
+
+	return 0;
+}
+
+/*
+ * If CPU and/or memory hotplug handlers, below, unplug any CPUs
+ * or memory nodes, we need to walk over the cpuset hierarchy,
+ * removing that CPU or node from all cpusets.  If this removes the
+ * last CPU or node from a cpuset, then move the tasks in the empty
+ * cpuset to its next-highest non-empty parent.
+ */
+static void remove_tasks_in_empty_cpuset(struct cpuset *cs)
+{
+	struct cpuset *parent;
+
+	/*
+	 * Find its next-highest non-empty parent, (top cpuset
+	 * has online cpus, so can't be empty).
+	 */
+	parent = parent_cs(cs);
+	while (cpumask_empty(parent->cpus_allowed) ||
+			nodes_empty(parent->mems_allowed))
+		parent = parent_cs(parent);
+
+	if (cgroup_transfer_tasks(parent->css.cgroup, cs->css.cgroup)) {
+		pr_err("cpuset: failed to transfer tasks out of empty cpuset ");
+		pr_cont_cgroup_name(cs->css.cgroup);
+		pr_cont("\n");
+	}
+}
+
+static void
+hotplug_update_tasks_legacy(struct cpuset *cs,
+			    struct cpumask *new_cpus, nodemask_t *new_mems,
+			    bool cpus_updated, bool mems_updated)
+{
+	bool is_empty;
+
+	spin_lock_irq(&callback_lock);
+	cpumask_copy(cs->cpus_allowed, new_cpus);
+	cpumask_copy(cs->effective_cpus, new_cpus);
+	cs->mems_allowed = *new_mems;
+	cs->effective_mems = *new_mems;
+	spin_unlock_irq(&callback_lock);
+
+	/*
+	 * Don't call update_tasks_cpumask() if the cpuset becomes empty,
+	 * as the tasks will be migratecd to an ancestor.
+	 */
+	if (cpus_updated && !cpumask_empty(cs->cpus_allowed))
+		update_tasks_cpumask(cs);
+	if (mems_updated && !nodes_empty(cs->mems_allowed))
+		update_tasks_nodemask(cs);
+
+	is_empty = cpumask_empty(cs->cpus_allowed) ||
+		   nodes_empty(cs->mems_allowed);
+
+	mutex_unlock(&cpuset_mutex);
+
+	/*
+	 * Move tasks to the nearest ancestor with execution resources,
+	 * This is full cgroup operation which will also call back into
+	 * cpuset. Should be done outside any lock.
+	 */
+	if (is_empty)
+		remove_tasks_in_empty_cpuset(cs);
+
+	mutex_lock(&cpuset_mutex);
+}
+
+static void
+hotplug_update_tasks(struct cpuset *cs,
+		     struct cpumask *new_cpus, nodemask_t *new_mems,
+		     bool cpus_updated, bool mems_updated)
+{
+	if (cpumask_empty(new_cpus))
+		cpumask_copy(new_cpus, parent_cs(cs)->effective_cpus);
+	if (nodes_empty(*new_mems))
+		*new_mems = parent_cs(cs)->effective_mems;
+
+	spin_lock_irq(&callback_lock);
+	cpumask_copy(cs->effective_cpus, new_cpus);
+	cs->effective_mems = *new_mems;
+	spin_unlock_irq(&callback_lock);
+
+	if (cpus_updated)
+		update_tasks_cpumask(cs);
+	if (mems_updated)
+		update_tasks_nodemask(cs);
+}
+
+/**
+ * cpuset_hotplug_update_tasks - update tasks in a cpuset for hotunplug
+ * @cs: cpuset in interest
+ *
+ * Compare @cs's cpu and mem masks against top_cpuset and if some have gone
+ * offline, update @cs accordingly.  If @cs ends up with no CPU or memory,
+ * all its tasks are moved to the nearest ancestor with both resources.
+ */
+static void cpuset_hotplug_update_tasks(struct cpuset *cs)
+{
+	static cpumask_t new_cpus;
+	static nodemask_t new_mems;
+	bool cpus_updated;
+	bool mems_updated;
+retry:
+	wait_event(cpuset_attach_wq, cs->attach_in_progress == 0);
+
+	mutex_lock(&cpuset_mutex);
+
+	/*
+	 * We have raced with task attaching. We wait until attaching
+	 * is finished, so we won't attach a task to an empty cpuset.
+	 */
+	if (cs->attach_in_progress) {
+		mutex_unlock(&cpuset_mutex);
+		goto retry;
+	}
+
+	cpumask_and(&new_cpus, cs->cpus_allowed, parent_cs(cs)->effective_cpus);
+	nodes_and(new_mems, cs->mems_allowed, parent_cs(cs)->effective_mems);
+
+	cpus_updated = !cpumask_equal(&new_cpus, cs->effective_cpus);
+	mems_updated = !nodes_equal(new_mems, cs->effective_mems);
+
+	if (is_in_v2_mode())
+		hotplug_update_tasks(cs, &new_cpus, &new_mems,
+				     cpus_updated, mems_updated);
+	else
+		hotplug_update_tasks_legacy(cs, &new_cpus, &new_mems,
+					    cpus_updated, mems_updated);
+
+	mutex_unlock(&cpuset_mutex);
+}
+
+static bool force_rebuild;
+
+void cpuset_force_rebuild(void)
+{
+	force_rebuild = true;
+}
+
+/**
+ * cpuset_hotplug_workfn - handle CPU/memory hotunplug for a cpuset
+ *
+ * This function is called after either CPU or memory configuration has
+ * changed and updates cpuset accordingly.  The top_cpuset is always
+ * synchronized to cpu_active_mask and N_MEMORY, which is necessary in
+ * order to make cpusets transparent (of no affect) on systems that are
+ * actively using CPU hotplug but making no active use of cpusets.
+ *
+ * Non-root cpusets are only affected by offlining.  If any CPUs or memory
+ * nodes have been taken down, cpuset_hotplug_update_tasks() is invoked on
+ * all descendants.
+ *
+ * Note that CPU offlining during suspend is ignored.  We don't modify
+ * cpusets across suspend/resume cycles at all.
+ */
+static void cpuset_hotplug_workfn(struct work_struct *work)
+{
+	static cpumask_t new_cpus;
+	static nodemask_t new_mems;
+	bool cpus_updated, mems_updated;
+	bool on_dfl = is_in_v2_mode();
+
+	mutex_lock(&cpuset_mutex);
+
+	/* fetch the available cpus/mems and find out which changed how */
+	cpumask_copy(&new_cpus, cpu_active_mask);
+	new_mems = node_states[N_MEMORY];
+
+	cpus_updated = !cpumask_equal(top_cpuset.effective_cpus, &new_cpus);
+	mems_updated = !nodes_equal(top_cpuset.effective_mems, new_mems);
+
+	/* synchronize cpus_allowed to cpu_active_mask */
+	if (cpus_updated) {
+		spin_lock_irq(&callback_lock);
+		if (!on_dfl)
+			cpumask_copy(top_cpuset.cpus_allowed, &new_cpus);
+		cpumask_copy(top_cpuset.effective_cpus, &new_cpus);
+		spin_unlock_irq(&callback_lock);
+		/* we don't mess with cpumasks of tasks in top_cpuset */
+	}
+
+	/* synchronize mems_allowed to N_MEMORY */
+	if (mems_updated) {
+		spin_lock_irq(&callback_lock);
+		if (!on_dfl)
+			top_cpuset.mems_allowed = new_mems;
+		top_cpuset.effective_mems = new_mems;
+		spin_unlock_irq(&callback_lock);
+		update_tasks_nodemask(&top_cpuset);
+	}
+
+	mutex_unlock(&cpuset_mutex);
+
+	/* if cpus or mems changed, we need to propagate to descendants */
+	if (cpus_updated || mems_updated) {
+		struct cpuset *cs;
+		struct cgroup_subsys_state *pos_css;
+
+		rcu_read_lock();
+		cpuset_for_each_descendant_pre(cs, pos_css, &top_cpuset) {
+			if (cs == &top_cpuset || !css_tryget_online(&cs->css))
+				continue;
+			rcu_read_unlock();
+
+			cpuset_hotplug_update_tasks(cs);
+
+			rcu_read_lock();
+			css_put(&cs->css);
+		}
+		rcu_read_unlock();
+	}
+
+	/* rebuild sched domains if cpus_allowed has changed */
+	if (cpus_updated || force_rebuild) {
+		force_rebuild = false;
+		rebuild_sched_domains();
+	}
+}
+
+void cpuset_update_active_cpus(void)
+{
+	/*
+	 * We're inside cpu hotplug critical region which usually nests
+	 * inside cgroup synchronization.  Bounce actual hotplug processing
+	 * to a work item to avoid reverse locking order.
+	 */
+	schedule_work(&cpuset_hotplug_work);
+}
+
+void cpuset_wait_for_hotplug(void)
+{
+	flush_work(&cpuset_hotplug_work);
+}
+
+/*
+ * Keep top_cpuset.mems_allowed tracking node_states[N_MEMORY].
+ * Call this routine anytime after node_states[N_MEMORY] changes.
+ * See cpuset_update_active_cpus() for CPU hotplug handling.
+ */
+static int cpuset_track_online_nodes(struct notifier_block *self,
+				unsigned long action, void *arg)
+{
+	schedule_work(&cpuset_hotplug_work);
+	return NOTIFY_OK;
+}
+
+static struct notifier_block cpuset_track_online_nodes_nb = {
+	.notifier_call = cpuset_track_online_nodes,
+	.priority = 10,		/* ??! */
+};
+
+/**
+ * cpuset_init_smp - initialize cpus_allowed
+ *
+ * Description: Finish top cpuset after cpu, node maps are initialized
+ */
+void __init cpuset_init_smp(void)
+{
+	/*
+	 * cpus_allowd/mems_allowed set to v2 values in the initial
+	 * cpuset_bind() call will be reset to v1 values in another
+	 * cpuset_bind() call when v1 cpuset is mounted.
+	 */
+	top_cpuset.old_mems_allowed = top_cpuset.mems_allowed;
+
+	cpumask_copy(top_cpuset.effective_cpus, cpu_active_mask);
+	top_cpuset.effective_mems = node_states[N_MEMORY];
+
+	register_hotmemory_notifier(&cpuset_track_online_nodes_nb);
+
+	cpuset_migrate_mm_wq = alloc_ordered_workqueue("cpuset_migrate_mm", 0);
+	BUG_ON(!cpuset_migrate_mm_wq);
+}
+
+/**
+ * cpuset_cpus_allowed - return cpus_allowed mask from a tasks cpuset.
+ * @tsk: pointer to task_struct from which to obtain cpuset->cpus_allowed.
+ * @pmask: pointer to struct cpumask variable to receive cpus_allowed set.
+ *
+ * Description: Returns the cpumask_var_t cpus_allowed of the cpuset
+ * attached to the specified @tsk.  Guaranteed to return some non-empty
+ * subset of cpu_online_mask, even if this means going outside the
+ * tasks cpuset.
+ **/
+
+void cpuset_cpus_allowed(struct task_struct *tsk, struct cpumask *pmask)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&callback_lock, flags);
+	rcu_read_lock();
+	guarantee_online_cpus(task_cs(tsk), pmask);
+	rcu_read_unlock();
+	spin_unlock_irqrestore(&callback_lock, flags);
+}
+
+/**
+ * cpuset_cpus_allowed_fallback - final fallback before complete catastrophe.
+ * @tsk: pointer to task_struct with which the scheduler is struggling
+ *
+ * Description: In the case that the scheduler cannot find an allowed cpu in
+ * tsk->cpus_allowed, we fall back to task_cs(tsk)->cpus_allowed. In legacy
+ * mode however, this value is the same as task_cs(tsk)->effective_cpus,
+ * which will not contain a sane cpumask during cases such as cpu hotplugging.
+ * This is the absolute last resort for the scheduler and it is only used if
+ * _every_ other avenue has been traveled.
+ **/
+
+void cpuset_cpus_allowed_fallback(struct task_struct *tsk)
+{
+	rcu_read_lock();
+	do_set_cpus_allowed(tsk, is_in_v2_mode() ?
+		task_cs(tsk)->cpus_allowed : cpu_possible_mask);
+	rcu_read_unlock();
+
+	/*
+	 * We own tsk->cpus_allowed, nobody can change it under us.
+	 *
+	 * But we used cs && cs->cpus_allowed lockless and thus can
+	 * race with cgroup_attach_task() or update_cpumask() and get
+	 * the wrong tsk->cpus_allowed. However, both cases imply the
+	 * subsequent cpuset_change_cpumask()->set_cpus_allowed_ptr()
+	 * which takes task_rq_lock().
+	 *
+	 * If we are called after it dropped the lock we must see all
+	 * changes in tsk_cs()->cpus_allowed. Otherwise we can temporary
+	 * set any mask even if it is not right from task_cs() pov,
+	 * the pending set_cpus_allowed_ptr() will fix things.
+	 *
+	 * select_fallback_rq() will fix things ups and set cpu_possible_mask
+	 * if required.
+	 */
+}
+
+void __init cpuset_init_current_mems_allowed(void)
+{
+	nodes_setall(current->mems_allowed);
+}
+
+/**
+ * cpuset_mems_allowed - return mems_allowed mask from a tasks cpuset.
+ * @tsk: pointer to task_struct from which to obtain cpuset->mems_allowed.
+ *
+ * Description: Returns the nodemask_t mems_allowed of the cpuset
+ * attached to the specified @tsk.  Guaranteed to return some non-empty
+ * subset of node_states[N_MEMORY], even if this means going outside the
+ * tasks cpuset.
+ **/
+
+nodemask_t cpuset_mems_allowed(struct task_struct *tsk)
+{
+	nodemask_t mask;
+	unsigned long flags;
+
+	spin_lock_irqsave(&callback_lock, flags);
+	rcu_read_lock();
+	guarantee_online_mems(task_cs(tsk), &mask);
+	rcu_read_unlock();
+	spin_unlock_irqrestore(&callback_lock, flags);
+
+	return mask;
+}
+
+/**
+ * cpuset_nodemask_valid_mems_allowed - check nodemask vs. curremt mems_allowed
+ * @nodemask: the nodemask to be checked
+ *
+ * Are any of the nodes in the nodemask allowed in current->mems_allowed?
+ */
+int cpuset_nodemask_valid_mems_allowed(nodemask_t *nodemask)
+{
+	return nodes_intersects(*nodemask, current->mems_allowed);
+}
+
+/*
+ * nearest_hardwall_ancestor() - Returns the nearest mem_exclusive or
+ * mem_hardwall ancestor to the specified cpuset.  Call holding
+ * callback_lock.  If no ancestor is mem_exclusive or mem_hardwall
+ * (an unusual configuration), then returns the root cpuset.
+ */
+static struct cpuset *nearest_hardwall_ancestor(struct cpuset *cs)
+{
+	while (!(is_mem_exclusive(cs) || is_mem_hardwall(cs)) && parent_cs(cs))
+		cs = parent_cs(cs);
+	return cs;
+}
+
+/**
+ * cpuset_node_allowed - Can we allocate on a memory node?
+ * @node: is this an allowed node?
+ * @gfp_mask: memory allocation flags
+ *
+ * If we're in interrupt, yes, we can always allocate.  If @node is set in
+ * current's mems_allowed, yes.  If it's not a __GFP_HARDWALL request and this
+ * node is set in the nearest hardwalled cpuset ancestor to current's cpuset,
+ * yes.  If current has access to memory reserves as an oom victim, yes.
+ * Otherwise, no.
+ *
+ * GFP_USER allocations are marked with the __GFP_HARDWALL bit,
+ * and do not allow allocations outside the current tasks cpuset
+ * unless the task has been OOM killed.
+ * GFP_KERNEL allocations are not so marked, so can escape to the
+ * nearest enclosing hardwalled ancestor cpuset.
+ *
+ * Scanning up parent cpusets requires callback_lock.  The
+ * __alloc_pages() routine only calls here with __GFP_HARDWALL bit
+ * _not_ set if it's a GFP_KERNEL allocation, and all nodes in the
+ * current tasks mems_allowed came up empty on the first pass over
+ * the zonelist.  So only GFP_KERNEL allocations, if all nodes in the
+ * cpuset are short of memory, might require taking the callback_lock.
+ *
+ * The first call here from mm/page_alloc:get_page_from_freelist()
+ * has __GFP_HARDWALL set in gfp_mask, enforcing hardwall cpusets,
+ * so no allocation on a node outside the cpuset is allowed (unless
+ * in interrupt, of course).
+ *
+ * The second pass through get_page_from_freelist() doesn't even call
+ * here for GFP_ATOMIC calls.  For those calls, the __alloc_pages()
+ * variable 'wait' is not set, and the bit ALLOC_CPUSET is not set
+ * in alloc_flags.  That logic and the checks below have the combined
+ * affect that:
+ *	in_interrupt - any node ok (current task context irrelevant)
+ *	GFP_ATOMIC   - any node ok
+ *	tsk_is_oom_victim   - any node ok
+ *	GFP_KERNEL   - any node in enclosing hardwalled cpuset ok
+ *	GFP_USER     - only nodes in current tasks mems allowed ok.
+ */
+bool __cpuset_node_allowed(int node, gfp_t gfp_mask)
+{
+	struct cpuset *cs;		/* current cpuset ancestors */
+	int allowed;			/* is allocation in zone z allowed? */
+	unsigned long flags;
+
+	if (in_interrupt())
+		return true;
+	if (node_isset(node, current->mems_allowed))
+		return true;
+	/*
+	 * Allow tasks that have access to memory reserves because they have
+	 * been OOM killed to get memory anywhere.
+	 */
+	if (unlikely(tsk_is_oom_victim(current)))
+		return true;
+	if (gfp_mask & __GFP_HARDWALL)	/* If hardwall request, stop here */
+		return false;
+
+	if (current->flags & PF_EXITING) /* Let dying task have memory */
+		return true;
+
+	/* Not hardwall and node outside mems_allowed: scan up cpusets */
+	spin_lock_irqsave(&callback_lock, flags);
+
+	rcu_read_lock();
+	cs = nearest_hardwall_ancestor(task_cs(current));
+	allowed = node_isset(node, cs->mems_allowed);
+	rcu_read_unlock();
+
+	spin_unlock_irqrestore(&callback_lock, flags);
+	return allowed;
+}
+
+/**
+ * cpuset_mem_spread_node() - On which node to begin search for a file page
+ * cpuset_slab_spread_node() - On which node to begin search for a slab page
+ *
+ * If a task is marked PF_SPREAD_PAGE or PF_SPREAD_SLAB (as for
+ * tasks in a cpuset with is_spread_page or is_spread_slab set),
+ * and if the memory allocation used cpuset_mem_spread_node()
+ * to determine on which node to start looking, as it will for
+ * certain page cache or slab cache pages such as used for file
+ * system buffers and inode caches, then instead of starting on the
+ * local node to look for a free page, rather spread the starting
+ * node around the tasks mems_allowed nodes.
+ *
+ * We don't have to worry about the returned node being offline
+ * because "it can't happen", and even if it did, it would be ok.
+ *
+ * The routines calling guarantee_online_mems() are careful to
+ * only set nodes in task->mems_allowed that are online.  So it
+ * should not be possible for the following code to return an
+ * offline node.  But if it did, that would be ok, as this routine
+ * is not returning the node where the allocation must be, only
+ * the node where the search should start.  The zonelist passed to
+ * __alloc_pages() will include all nodes.  If the slab allocator
+ * is passed an offline node, it will fall back to the local node.
+ * See kmem_cache_alloc_node().
+ */
+
+static int cpuset_spread_node(int *rotor)
+{
+	return *rotor = next_node_in(*rotor, current->mems_allowed);
+}
+
+int cpuset_mem_spread_node(void)
+{
+	if (current->cpuset_mem_spread_rotor == NUMA_NO_NODE)
+		current->cpuset_mem_spread_rotor =
+			node_random(&current->mems_allowed);
+
+	return cpuset_spread_node(&current->cpuset_mem_spread_rotor);
+}
+
+int cpuset_slab_spread_node(void)
+{
+	if (current->cpuset_slab_spread_rotor == NUMA_NO_NODE)
+		current->cpuset_slab_spread_rotor =
+			node_random(&current->mems_allowed);
+
+	return cpuset_spread_node(&current->cpuset_slab_spread_rotor);
+}
+
+EXPORT_SYMBOL_GPL(cpuset_mem_spread_node);
+
+/**
+ * cpuset_mems_allowed_intersects - Does @tsk1's mems_allowed intersect @tsk2's?
+ * @tsk1: pointer to task_struct of some task.
+ * @tsk2: pointer to task_struct of some other task.
+ *
+ * Description: Return true if @tsk1's mems_allowed intersects the
+ * mems_allowed of @tsk2.  Used by the OOM killer to determine if
+ * one of the task's memory usage might impact the memory available
+ * to the other.
+ **/
+
+int cpuset_mems_allowed_intersects(const struct task_struct *tsk1,
+				   const struct task_struct *tsk2)
+{
+	return nodes_intersects(tsk1->mems_allowed, tsk2->mems_allowed);
+}
+
+/**
+ * cpuset_print_current_mems_allowed - prints current's cpuset and mems_allowed
+ *
+ * Description: Prints current's name, cpuset name, and cached copy of its
+ * mems_allowed to the kernel log.
+ */
+void cpuset_print_current_mems_allowed(void)
+{
+	struct cgroup *cgrp;
+
+	rcu_read_lock();
+
+	cgrp = task_cs(current)->css.cgroup;
+	pr_info("%s cpuset=", current->comm);
+	pr_cont_cgroup_name(cgrp);
+	pr_cont(" mems_allowed=%*pbl\n",
+		nodemask_pr_args(&current->mems_allowed));
+
+	rcu_read_unlock();
+}
+
+/*
+ * Collection of memory_pressure is suppressed unless
+ * this flag is enabled by writing "1" to the special
+ * cpuset file 'memory_pressure_enabled' in the root cpuset.
+ */
+
+int cpuset_memory_pressure_enabled __read_mostly;
+
+/**
+ * cpuset_memory_pressure_bump - keep stats of per-cpuset reclaims.
+ *
+ * Keep a running average of the rate of synchronous (direct)
+ * page reclaim efforts initiated by tasks in each cpuset.
+ *
+ * This represents the rate at which some task in the cpuset
+ * ran low on memory on all nodes it was allowed to use, and
+ * had to enter the kernels page reclaim code in an effort to
+ * create more free memory by tossing clean pages or swapping
+ * or writing dirty pages.
+ *
+ * Display to user space in the per-cpuset read-only file
+ * "memory_pressure".  Value displayed is an integer
+ * representing the recent rate of entry into the synchronous
+ * (direct) page reclaim by any task attached to the cpuset.
+ **/
+
+void __cpuset_memory_pressure_bump(void)
+{
+	rcu_read_lock();
+	fmeter_markevent(&task_cs(current)->fmeter);
+	rcu_read_unlock();
+}
+
+#ifdef CONFIG_PROC_PID_CPUSET
+/*
+ * proc_cpuset_show()
+ *  - Print tasks cpuset path into seq_file.
+ *  - Used for /proc/<pid>/cpuset.
+ *  - No need to task_lock(tsk) on this tsk->cpuset reference, as it
+ *    doesn't really matter if tsk->cpuset changes after we read it,
+ *    and we take cpuset_mutex, keeping cpuset_attach() from changing it
+ *    anyway.
+ */
+int proc_cpuset_show(struct seq_file *m, struct pid_namespace *ns,
+		     struct pid *pid, struct task_struct *tsk)
+{
+	char *buf;
+	struct cgroup_subsys_state *css;
+	int retval;
+
+	retval = -ENOMEM;
+	buf = kmalloc(PATH_MAX, GFP_KERNEL);
+	if (!buf)
+		goto out;
+
+	css = task_get_css(tsk, cpuset_cgrp_id);
+	retval = cgroup_path_ns(css->cgroup, buf, PATH_MAX,
+				current->nsproxy->cgroup_ns);
+	css_put(css);
+	if (retval >= PATH_MAX)
+		retval = -ENAMETOOLONG;
+	if (retval < 0)
+		goto out_free;
+	seq_puts(m, buf);
+	seq_putc(m, '\n');
+	retval = 0;
+out_free:
+	kfree(buf);
+out:
+	return retval;
+}
+#endif /* CONFIG_PROC_PID_CPUSET */
+
+/* Display task mems_allowed in /proc/<pid>/status file. */
+void cpuset_task_status_allowed(struct seq_file *m, struct task_struct *task)
+{
+	seq_printf(m, "Mems_allowed:\t%*pb\n",
+		   nodemask_pr_args(&task->mems_allowed));
+	seq_printf(m, "Mems_allowed_list:\t%*pbl\n",
+		   nodemask_pr_args(&task->mems_allowed));
+}
diff --git a/kernel/cgroup/debug.c b/kernel/cgroup/debug.c
new file mode 100644
index 000000000..9caeda610
--- /dev/null
+++ b/kernel/cgroup/debug.c
@@ -0,0 +1,383 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Debug controller
+ *
+ * WARNING: This controller is for cgroup core debugging only.
+ * Its interfaces are unstable and subject to changes at any time.
+ */
+#include <linux/ctype.h>
+#include <linux/mm.h>
+#include <linux/slab.h>
+
+#include "cgroup-internal.h"
+
+static struct cgroup_subsys_state *
+debug_css_alloc(struct cgroup_subsys_state *parent_css)
+{
+	struct cgroup_subsys_state *css = kzalloc(sizeof(*css), GFP_KERNEL);
+
+	if (!css)
+		return ERR_PTR(-ENOMEM);
+
+	return css;
+}
+
+static void debug_css_free(struct cgroup_subsys_state *css)
+{
+	kfree(css);
+}
+
+/*
+ * debug_taskcount_read - return the number of tasks in a cgroup.
+ * @cgrp: the cgroup in question
+ */
+static u64 debug_taskcount_read(struct cgroup_subsys_state *css,
+				struct cftype *cft)
+{
+	return cgroup_task_count(css->cgroup);
+}
+
+static int current_css_set_read(struct seq_file *seq, void *v)
+{
+	struct kernfs_open_file *of = seq->private;
+	struct css_set *cset;
+	struct cgroup_subsys *ss;
+	struct cgroup_subsys_state *css;
+	int i, refcnt;
+
+	if (!cgroup_kn_lock_live(of->kn, false))
+		return -ENODEV;
+
+	spin_lock_irq(&css_set_lock);
+	rcu_read_lock();
+	cset = task_css_set(current);
+	refcnt = refcount_read(&cset->refcount);
+	seq_printf(seq, "css_set %pK %d", cset, refcnt);
+	if (refcnt > cset->nr_tasks)
+		seq_printf(seq, " +%d", refcnt - cset->nr_tasks);
+	seq_puts(seq, "\n");
+
+	/*
+	 * Print the css'es stored in the current css_set.
+	 */
+	for_each_subsys(ss, i) {
+		css = cset->subsys[ss->id];
+		if (!css)
+			continue;
+		seq_printf(seq, "%2d: %-4s\t- %lx[%d]\n", ss->id, ss->name,
+			  (unsigned long)css, css->id);
+	}
+	rcu_read_unlock();
+	spin_unlock_irq(&css_set_lock);
+	cgroup_kn_unlock(of->kn);
+	return 0;
+}
+
+static u64 current_css_set_refcount_read(struct cgroup_subsys_state *css,
+					 struct cftype *cft)
+{
+	u64 count;
+
+	rcu_read_lock();
+	count = refcount_read(&task_css_set(current)->refcount);
+	rcu_read_unlock();
+	return count;
+}
+
+static int current_css_set_cg_links_read(struct seq_file *seq, void *v)
+{
+	struct cgrp_cset_link *link;
+	struct css_set *cset;
+	char *name_buf;
+
+	name_buf = kmalloc(NAME_MAX + 1, GFP_KERNEL);
+	if (!name_buf)
+		return -ENOMEM;
+
+	spin_lock_irq(&css_set_lock);
+	rcu_read_lock();
+	cset = task_css_set(current);
+	list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
+		struct cgroup *c = link->cgrp;
+
+		cgroup_name(c, name_buf, NAME_MAX + 1);
+		seq_printf(seq, "Root %d group %s\n",
+			   c->root->hierarchy_id, name_buf);
+	}
+	rcu_read_unlock();
+	spin_unlock_irq(&css_set_lock);
+	kfree(name_buf);
+	return 0;
+}
+
+#define MAX_TASKS_SHOWN_PER_CSS 25
+static int cgroup_css_links_read(struct seq_file *seq, void *v)
+{
+	struct cgroup_subsys_state *css = seq_css(seq);
+	struct cgrp_cset_link *link;
+	int dead_cnt = 0, extra_refs = 0, threaded_csets = 0;
+
+	spin_lock_irq(&css_set_lock);
+
+	list_for_each_entry(link, &css->cgroup->cset_links, cset_link) {
+		struct css_set *cset = link->cset;
+		struct task_struct *task;
+		int count = 0;
+		int refcnt = refcount_read(&cset->refcount);
+
+		/*
+		 * Print out the proc_cset and threaded_cset relationship
+		 * and highlight difference between refcount and task_count.
+		 */
+		seq_printf(seq, "css_set %pK", cset);
+		if (rcu_dereference_protected(cset->dom_cset, 1) != cset) {
+			threaded_csets++;
+			seq_printf(seq, "=>%pK", cset->dom_cset);
+		}
+		if (!list_empty(&cset->threaded_csets)) {
+			struct css_set *tcset;
+			int idx = 0;
+
+			list_for_each_entry(tcset, &cset->threaded_csets,
+					    threaded_csets_node) {
+				seq_puts(seq, idx ? "," : "<=");
+				seq_printf(seq, "%pK", tcset);
+				idx++;
+			}
+		} else {
+			seq_printf(seq, " %d", refcnt);
+			if (refcnt - cset->nr_tasks > 0) {
+				int extra = refcnt - cset->nr_tasks;
+
+				seq_printf(seq, " +%d", extra);
+				/*
+				 * Take out the one additional reference in
+				 * init_css_set.
+				 */
+				if (cset == &init_css_set)
+					extra--;
+				extra_refs += extra;
+			}
+		}
+		seq_puts(seq, "\n");
+
+		list_for_each_entry(task, &cset->tasks, cg_list) {
+			if (count++ <= MAX_TASKS_SHOWN_PER_CSS)
+				seq_printf(seq, "  task %d\n",
+					   task_pid_vnr(task));
+		}
+
+		list_for_each_entry(task, &cset->mg_tasks, cg_list) {
+			if (count++ <= MAX_TASKS_SHOWN_PER_CSS)
+				seq_printf(seq, "  task %d\n",
+					   task_pid_vnr(task));
+		}
+		/* show # of overflowed tasks */
+		if (count > MAX_TASKS_SHOWN_PER_CSS)
+			seq_printf(seq, "  ... (%d)\n",
+				   count - MAX_TASKS_SHOWN_PER_CSS);
+
+		if (cset->dead) {
+			seq_puts(seq, "    [dead]\n");
+			dead_cnt++;
+		}
+
+		WARN_ON(count != cset->nr_tasks);
+	}
+	spin_unlock_irq(&css_set_lock);
+
+	if (!dead_cnt && !extra_refs && !threaded_csets)
+		return 0;
+
+	seq_puts(seq, "\n");
+	if (threaded_csets)
+		seq_printf(seq, "threaded css_sets = %d\n", threaded_csets);
+	if (extra_refs)
+		seq_printf(seq, "extra references = %d\n", extra_refs);
+	if (dead_cnt)
+		seq_printf(seq, "dead css_sets = %d\n", dead_cnt);
+
+	return 0;
+}
+
+static int cgroup_subsys_states_read(struct seq_file *seq, void *v)
+{
+	struct kernfs_open_file *of = seq->private;
+	struct cgroup *cgrp;
+	struct cgroup_subsys *ss;
+	struct cgroup_subsys_state *css;
+	char pbuf[16];
+	int i;
+
+	cgrp = cgroup_kn_lock_live(of->kn, false);
+	if (!cgrp)
+		return -ENODEV;
+
+	for_each_subsys(ss, i) {
+		css = rcu_dereference_check(cgrp->subsys[ss->id], true);
+		if (!css)
+			continue;
+
+		pbuf[0] = '\0';
+
+		/* Show the parent CSS if applicable*/
+		if (css->parent)
+			snprintf(pbuf, sizeof(pbuf) - 1, " P=%d",
+				 css->parent->id);
+		seq_printf(seq, "%2d: %-4s\t- %lx[%d] %d%s\n", ss->id, ss->name,
+			  (unsigned long)css, css->id,
+			  atomic_read(&css->online_cnt), pbuf);
+	}
+
+	cgroup_kn_unlock(of->kn);
+	return 0;
+}
+
+static void cgroup_masks_read_one(struct seq_file *seq, const char *name,
+				  u16 mask)
+{
+	struct cgroup_subsys *ss;
+	int ssid;
+	bool first = true;
+
+	seq_printf(seq, "%-17s: ", name);
+	for_each_subsys(ss, ssid) {
+		if (!(mask & (1 << ssid)))
+			continue;
+		if (!first)
+			seq_puts(seq, ", ");
+		seq_puts(seq, ss->name);
+		first = false;
+	}
+	seq_putc(seq, '\n');
+}
+
+static int cgroup_masks_read(struct seq_file *seq, void *v)
+{
+	struct kernfs_open_file *of = seq->private;
+	struct cgroup *cgrp;
+
+	cgrp = cgroup_kn_lock_live(of->kn, false);
+	if (!cgrp)
+		return -ENODEV;
+
+	cgroup_masks_read_one(seq, "subtree_control", cgrp->subtree_control);
+	cgroup_masks_read_one(seq, "subtree_ss_mask", cgrp->subtree_ss_mask);
+
+	cgroup_kn_unlock(of->kn);
+	return 0;
+}
+
+static u64 releasable_read(struct cgroup_subsys_state *css, struct cftype *cft)
+{
+	return (!cgroup_is_populated(css->cgroup) &&
+		!css_has_online_children(&css->cgroup->self));
+}
+
+static struct cftype debug_legacy_files[] =  {
+	{
+		.name = "taskcount",
+		.read_u64 = debug_taskcount_read,
+	},
+
+	{
+		.name = "current_css_set",
+		.seq_show = current_css_set_read,
+		.flags = CFTYPE_ONLY_ON_ROOT,
+	},
+
+	{
+		.name = "current_css_set_refcount",
+		.read_u64 = current_css_set_refcount_read,
+		.flags = CFTYPE_ONLY_ON_ROOT,
+	},
+
+	{
+		.name = "current_css_set_cg_links",
+		.seq_show = current_css_set_cg_links_read,
+		.flags = CFTYPE_ONLY_ON_ROOT,
+	},
+
+	{
+		.name = "cgroup_css_links",
+		.seq_show = cgroup_css_links_read,
+	},
+
+	{
+		.name = "cgroup_subsys_states",
+		.seq_show = cgroup_subsys_states_read,
+	},
+
+	{
+		.name = "cgroup_masks",
+		.seq_show = cgroup_masks_read,
+	},
+
+	{
+		.name = "releasable",
+		.read_u64 = releasable_read,
+	},
+
+	{ }	/* terminate */
+};
+
+static struct cftype debug_files[] =  {
+	{
+		.name = "taskcount",
+		.read_u64 = debug_taskcount_read,
+	},
+
+	{
+		.name = "current_css_set",
+		.seq_show = current_css_set_read,
+		.flags = CFTYPE_ONLY_ON_ROOT,
+	},
+
+	{
+		.name = "current_css_set_refcount",
+		.read_u64 = current_css_set_refcount_read,
+		.flags = CFTYPE_ONLY_ON_ROOT,
+	},
+
+	{
+		.name = "current_css_set_cg_links",
+		.seq_show = current_css_set_cg_links_read,
+		.flags = CFTYPE_ONLY_ON_ROOT,
+	},
+
+	{
+		.name = "css_links",
+		.seq_show = cgroup_css_links_read,
+	},
+
+	{
+		.name = "csses",
+		.seq_show = cgroup_subsys_states_read,
+	},
+
+	{
+		.name = "masks",
+		.seq_show = cgroup_masks_read,
+	},
+
+	{ }	/* terminate */
+};
+
+struct cgroup_subsys debug_cgrp_subsys = {
+	.css_alloc	= debug_css_alloc,
+	.css_free	= debug_css_free,
+	.legacy_cftypes	= debug_legacy_files,
+};
+
+/*
+ * On v2, debug is an implicit controller enabled by "cgroup_debug" boot
+ * parameter.
+ */
+static int __init enable_cgroup_debug(char *str)
+{
+	debug_cgrp_subsys.dfl_cftypes = debug_files;
+	debug_cgrp_subsys.implicit_on_dfl = true;
+	debug_cgrp_subsys.threaded = true;
+	return 1;
+}
+__setup("cgroup_debug", enable_cgroup_debug);
diff --git a/kernel/cgroup/freezer.c b/kernel/cgroup/freezer.c
new file mode 100644
index 000000000..08236798d
--- /dev/null
+++ b/kernel/cgroup/freezer.c
@@ -0,0 +1,481 @@
+/*
+ * cgroup_freezer.c -  control group freezer subsystem
+ *
+ * Copyright IBM Corporation, 2007
+ *
+ * Author : Cedric Le Goater <clg@fr.ibm.com>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of version 2.1 of the GNU Lesser General Public License
+ * as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it would be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ */
+
+#include <linux/export.h>
+#include <linux/slab.h>
+#include <linux/cgroup.h>
+#include <linux/fs.h>
+#include <linux/uaccess.h>
+#include <linux/freezer.h>
+#include <linux/seq_file.h>
+#include <linux/mutex.h>
+
+/*
+ * A cgroup is freezing if any FREEZING flags are set.  FREEZING_SELF is
+ * set if "FROZEN" is written to freezer.state cgroupfs file, and cleared
+ * for "THAWED".  FREEZING_PARENT is set if the parent freezer is FREEZING
+ * for whatever reason.  IOW, a cgroup has FREEZING_PARENT set if one of
+ * its ancestors has FREEZING_SELF set.
+ */
+enum freezer_state_flags {
+	CGROUP_FREEZER_ONLINE	= (1 << 0), /* freezer is fully online */
+	CGROUP_FREEZING_SELF	= (1 << 1), /* this freezer is freezing */
+	CGROUP_FREEZING_PARENT	= (1 << 2), /* the parent freezer is freezing */
+	CGROUP_FROZEN		= (1 << 3), /* this and its descendants frozen */
+
+	/* mask for all FREEZING flags */
+	CGROUP_FREEZING		= CGROUP_FREEZING_SELF | CGROUP_FREEZING_PARENT,
+};
+
+struct freezer {
+	struct cgroup_subsys_state	css;
+	unsigned int			state;
+};
+
+static DEFINE_MUTEX(freezer_mutex);
+
+static inline struct freezer *css_freezer(struct cgroup_subsys_state *css)
+{
+	return css ? container_of(css, struct freezer, css) : NULL;
+}
+
+static inline struct freezer *task_freezer(struct task_struct *task)
+{
+	return css_freezer(task_css(task, freezer_cgrp_id));
+}
+
+static struct freezer *parent_freezer(struct freezer *freezer)
+{
+	return css_freezer(freezer->css.parent);
+}
+
+bool cgroup_freezing(struct task_struct *task)
+{
+	bool ret;
+
+	rcu_read_lock();
+	ret = task_freezer(task)->state & CGROUP_FREEZING;
+	rcu_read_unlock();
+
+	return ret;
+}
+
+static const char *freezer_state_strs(unsigned int state)
+{
+	if (state & CGROUP_FROZEN)
+		return "FROZEN";
+	if (state & CGROUP_FREEZING)
+		return "FREEZING";
+	return "THAWED";
+};
+
+static struct cgroup_subsys_state *
+freezer_css_alloc(struct cgroup_subsys_state *parent_css)
+{
+	struct freezer *freezer;
+
+	freezer = kzalloc(sizeof(struct freezer), GFP_KERNEL);
+	if (!freezer)
+		return ERR_PTR(-ENOMEM);
+
+	return &freezer->css;
+}
+
+/**
+ * freezer_css_online - commit creation of a freezer css
+ * @css: css being created
+ *
+ * We're committing to creation of @css.  Mark it online and inherit
+ * parent's freezing state while holding both parent's and our
+ * freezer->lock.
+ */
+static int freezer_css_online(struct cgroup_subsys_state *css)
+{
+	struct freezer *freezer = css_freezer(css);
+	struct freezer *parent = parent_freezer(freezer);
+
+	mutex_lock(&freezer_mutex);
+
+	freezer->state |= CGROUP_FREEZER_ONLINE;
+
+	if (parent && (parent->state & CGROUP_FREEZING)) {
+		freezer->state |= CGROUP_FREEZING_PARENT | CGROUP_FROZEN;
+		atomic_inc(&system_freezing_cnt);
+	}
+
+	mutex_unlock(&freezer_mutex);
+	return 0;
+}
+
+/**
+ * freezer_css_offline - initiate destruction of a freezer css
+ * @css: css being destroyed
+ *
+ * @css is going away.  Mark it dead and decrement system_freezing_count if
+ * it was holding one.
+ */
+static void freezer_css_offline(struct cgroup_subsys_state *css)
+{
+	struct freezer *freezer = css_freezer(css);
+
+	mutex_lock(&freezer_mutex);
+
+	if (freezer->state & CGROUP_FREEZING)
+		atomic_dec(&system_freezing_cnt);
+
+	freezer->state = 0;
+
+	mutex_unlock(&freezer_mutex);
+}
+
+static void freezer_css_free(struct cgroup_subsys_state *css)
+{
+	kfree(css_freezer(css));
+}
+
+/*
+ * Tasks can be migrated into a different freezer anytime regardless of its
+ * current state.  freezer_attach() is responsible for making new tasks
+ * conform to the current state.
+ *
+ * Freezer state changes and task migration are synchronized via
+ * @freezer->lock.  freezer_attach() makes the new tasks conform to the
+ * current state and all following state changes can see the new tasks.
+ */
+static void freezer_attach(struct cgroup_taskset *tset)
+{
+	struct task_struct *task;
+	struct cgroup_subsys_state *new_css;
+
+	mutex_lock(&freezer_mutex);
+
+	/*
+	 * Make the new tasks conform to the current state of @new_css.
+	 * For simplicity, when migrating any task to a FROZEN cgroup, we
+	 * revert it to FREEZING and let update_if_frozen() determine the
+	 * correct state later.
+	 *
+	 * Tasks in @tset are on @new_css but may not conform to its
+	 * current state before executing the following - !frozen tasks may
+	 * be visible in a FROZEN cgroup and frozen tasks in a THAWED one.
+	 */
+	cgroup_taskset_for_each(task, new_css, tset) {
+		struct freezer *freezer = css_freezer(new_css);
+
+		if (!(freezer->state & CGROUP_FREEZING)) {
+			__thaw_task(task);
+		} else {
+			freeze_task(task);
+			/* clear FROZEN and propagate upwards */
+			while (freezer && (freezer->state & CGROUP_FROZEN)) {
+				freezer->state &= ~CGROUP_FROZEN;
+				freezer = parent_freezer(freezer);
+			}
+		}
+	}
+
+	mutex_unlock(&freezer_mutex);
+}
+
+/**
+ * freezer_fork - cgroup post fork callback
+ * @task: a task which has just been forked
+ *
+ * @task has just been created and should conform to the current state of
+ * the cgroup_freezer it belongs to.  This function may race against
+ * freezer_attach().  Losing to freezer_attach() means that we don't have
+ * to do anything as freezer_attach() will put @task into the appropriate
+ * state.
+ */
+static void freezer_fork(struct task_struct *task)
+{
+	struct freezer *freezer;
+
+	/*
+	 * The root cgroup is non-freezable, so we can skip locking the
+	 * freezer.  This is safe regardless of race with task migration.
+	 * If we didn't race or won, skipping is obviously the right thing
+	 * to do.  If we lost and root is the new cgroup, noop is still the
+	 * right thing to do.
+	 */
+	if (task_css_is_root(task, freezer_cgrp_id))
+		return;
+
+	mutex_lock(&freezer_mutex);
+	rcu_read_lock();
+
+	freezer = task_freezer(task);
+	if (freezer->state & CGROUP_FREEZING)
+		freeze_task(task);
+
+	rcu_read_unlock();
+	mutex_unlock(&freezer_mutex);
+}
+
+/**
+ * update_if_frozen - update whether a cgroup finished freezing
+ * @css: css of interest
+ *
+ * Once FREEZING is initiated, transition to FROZEN is lazily updated by
+ * calling this function.  If the current state is FREEZING but not FROZEN,
+ * this function checks whether all tasks of this cgroup and the descendant
+ * cgroups finished freezing and, if so, sets FROZEN.
+ *
+ * The caller is responsible for grabbing RCU read lock and calling
+ * update_if_frozen() on all descendants prior to invoking this function.
+ *
+ * Task states and freezer state might disagree while tasks are being
+ * migrated into or out of @css, so we can't verify task states against
+ * @freezer state here.  See freezer_attach() for details.
+ */
+static void update_if_frozen(struct cgroup_subsys_state *css)
+{
+	struct freezer *freezer = css_freezer(css);
+	struct cgroup_subsys_state *pos;
+	struct css_task_iter it;
+	struct task_struct *task;
+
+	lockdep_assert_held(&freezer_mutex);
+
+	if (!(freezer->state & CGROUP_FREEZING) ||
+	    (freezer->state & CGROUP_FROZEN))
+		return;
+
+	/* are all (live) children frozen? */
+	rcu_read_lock();
+	css_for_each_child(pos, css) {
+		struct freezer *child = css_freezer(pos);
+
+		if ((child->state & CGROUP_FREEZER_ONLINE) &&
+		    !(child->state & CGROUP_FROZEN)) {
+			rcu_read_unlock();
+			return;
+		}
+	}
+	rcu_read_unlock();
+
+	/* are all tasks frozen? */
+	css_task_iter_start(css, 0, &it);
+
+	while ((task = css_task_iter_next(&it))) {
+		if (freezing(task)) {
+			/*
+			 * freezer_should_skip() indicates that the task
+			 * should be skipped when determining freezing
+			 * completion.  Consider it frozen in addition to
+			 * the usual frozen condition.
+			 */
+			if (!frozen(task) && !freezer_should_skip(task))
+				goto out_iter_end;
+		}
+	}
+
+	freezer->state |= CGROUP_FROZEN;
+out_iter_end:
+	css_task_iter_end(&it);
+}
+
+static int freezer_read(struct seq_file *m, void *v)
+{
+	struct cgroup_subsys_state *css = seq_css(m), *pos;
+
+	mutex_lock(&freezer_mutex);
+	rcu_read_lock();
+
+	/* update states bottom-up */
+	css_for_each_descendant_post(pos, css) {
+		if (!css_tryget_online(pos))
+			continue;
+		rcu_read_unlock();
+
+		update_if_frozen(pos);
+
+		rcu_read_lock();
+		css_put(pos);
+	}
+
+	rcu_read_unlock();
+	mutex_unlock(&freezer_mutex);
+
+	seq_puts(m, freezer_state_strs(css_freezer(css)->state));
+	seq_putc(m, '\n');
+	return 0;
+}
+
+static void freeze_cgroup(struct freezer *freezer)
+{
+	struct css_task_iter it;
+	struct task_struct *task;
+
+	css_task_iter_start(&freezer->css, 0, &it);
+	while ((task = css_task_iter_next(&it)))
+		freeze_task(task);
+	css_task_iter_end(&it);
+}
+
+static void unfreeze_cgroup(struct freezer *freezer)
+{
+	struct css_task_iter it;
+	struct task_struct *task;
+
+	css_task_iter_start(&freezer->css, 0, &it);
+	while ((task = css_task_iter_next(&it)))
+		__thaw_task(task);
+	css_task_iter_end(&it);
+}
+
+/**
+ * freezer_apply_state - apply state change to a single cgroup_freezer
+ * @freezer: freezer to apply state change to
+ * @freeze: whether to freeze or unfreeze
+ * @state: CGROUP_FREEZING_* flag to set or clear
+ *
+ * Set or clear @state on @cgroup according to @freeze, and perform
+ * freezing or thawing as necessary.
+ */
+static void freezer_apply_state(struct freezer *freezer, bool freeze,
+				unsigned int state)
+{
+	/* also synchronizes against task migration, see freezer_attach() */
+	lockdep_assert_held(&freezer_mutex);
+
+	if (!(freezer->state & CGROUP_FREEZER_ONLINE))
+		return;
+
+	if (freeze) {
+		if (!(freezer->state & CGROUP_FREEZING))
+			atomic_inc(&system_freezing_cnt);
+		freezer->state |= state;
+		freeze_cgroup(freezer);
+	} else {
+		bool was_freezing = freezer->state & CGROUP_FREEZING;
+
+		freezer->state &= ~state;
+
+		if (!(freezer->state & CGROUP_FREEZING)) {
+			if (was_freezing)
+				atomic_dec(&system_freezing_cnt);
+			freezer->state &= ~CGROUP_FROZEN;
+			unfreeze_cgroup(freezer);
+		}
+	}
+}
+
+/**
+ * freezer_change_state - change the freezing state of a cgroup_freezer
+ * @freezer: freezer of interest
+ * @freeze: whether to freeze or thaw
+ *
+ * Freeze or thaw @freezer according to @freeze.  The operations are
+ * recursive - all descendants of @freezer will be affected.
+ */
+static void freezer_change_state(struct freezer *freezer, bool freeze)
+{
+	struct cgroup_subsys_state *pos;
+
+	/*
+	 * Update all its descendants in pre-order traversal.  Each
+	 * descendant will try to inherit its parent's FREEZING state as
+	 * CGROUP_FREEZING_PARENT.
+	 */
+	mutex_lock(&freezer_mutex);
+	rcu_read_lock();
+	css_for_each_descendant_pre(pos, &freezer->css) {
+		struct freezer *pos_f = css_freezer(pos);
+		struct freezer *parent = parent_freezer(pos_f);
+
+		if (!css_tryget_online(pos))
+			continue;
+		rcu_read_unlock();
+
+		if (pos_f == freezer)
+			freezer_apply_state(pos_f, freeze,
+					    CGROUP_FREEZING_SELF);
+		else
+			freezer_apply_state(pos_f,
+					    parent->state & CGROUP_FREEZING,
+					    CGROUP_FREEZING_PARENT);
+
+		rcu_read_lock();
+		css_put(pos);
+	}
+	rcu_read_unlock();
+	mutex_unlock(&freezer_mutex);
+}
+
+static ssize_t freezer_write(struct kernfs_open_file *of,
+			     char *buf, size_t nbytes, loff_t off)
+{
+	bool freeze;
+
+	buf = strstrip(buf);
+
+	if (strcmp(buf, freezer_state_strs(0)) == 0)
+		freeze = false;
+	else if (strcmp(buf, freezer_state_strs(CGROUP_FROZEN)) == 0)
+		freeze = true;
+	else
+		return -EINVAL;
+
+	freezer_change_state(css_freezer(of_css(of)), freeze);
+	return nbytes;
+}
+
+static u64 freezer_self_freezing_read(struct cgroup_subsys_state *css,
+				      struct cftype *cft)
+{
+	struct freezer *freezer = css_freezer(css);
+
+	return (bool)(freezer->state & CGROUP_FREEZING_SELF);
+}
+
+static u64 freezer_parent_freezing_read(struct cgroup_subsys_state *css,
+					struct cftype *cft)
+{
+	struct freezer *freezer = css_freezer(css);
+
+	return (bool)(freezer->state & CGROUP_FREEZING_PARENT);
+}
+
+static struct cftype files[] = {
+	{
+		.name = "state",
+		.flags = CFTYPE_NOT_ON_ROOT,
+		.seq_show = freezer_read,
+		.write = freezer_write,
+	},
+	{
+		.name = "self_freezing",
+		.flags = CFTYPE_NOT_ON_ROOT,
+		.read_u64 = freezer_self_freezing_read,
+	},
+	{
+		.name = "parent_freezing",
+		.flags = CFTYPE_NOT_ON_ROOT,
+		.read_u64 = freezer_parent_freezing_read,
+	},
+	{ }	/* terminate */
+};
+
+struct cgroup_subsys freezer_cgrp_subsys = {
+	.css_alloc	= freezer_css_alloc,
+	.css_online	= freezer_css_online,
+	.css_offline	= freezer_css_offline,
+	.css_free	= freezer_css_free,
+	.attach		= freezer_attach,
+	.fork		= freezer_fork,
+	.legacy_cftypes	= files,
+};
diff --git a/kernel/cgroup/namespace.c b/kernel/cgroup/namespace.c
new file mode 100644
index 000000000..b05f1dd58
--- /dev/null
+++ b/kernel/cgroup/namespace.c
@@ -0,0 +1,156 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "cgroup-internal.h"
+
+#include <linux/sched/task.h>
+#include <linux/slab.h>
+#include <linux/nsproxy.h>
+#include <linux/proc_ns.h>
+
+
+/* cgroup namespaces */
+
+static struct ucounts *inc_cgroup_namespaces(struct user_namespace *ns)
+{
+	return inc_ucount(ns, current_euid(), UCOUNT_CGROUP_NAMESPACES);
+}
+
+static void dec_cgroup_namespaces(struct ucounts *ucounts)
+{
+	dec_ucount(ucounts, UCOUNT_CGROUP_NAMESPACES);
+}
+
+static struct cgroup_namespace *alloc_cgroup_ns(void)
+{
+	struct cgroup_namespace *new_ns;
+	int ret;
+
+	new_ns = kzalloc(sizeof(struct cgroup_namespace), GFP_KERNEL);
+	if (!new_ns)
+		return ERR_PTR(-ENOMEM);
+	ret = ns_alloc_inum(&new_ns->ns);
+	if (ret) {
+		kfree(new_ns);
+		return ERR_PTR(ret);
+	}
+	refcount_set(&new_ns->count, 1);
+	new_ns->ns.ops = &cgroupns_operations;
+	return new_ns;
+}
+
+void free_cgroup_ns(struct cgroup_namespace *ns)
+{
+	put_css_set(ns->root_cset);
+	dec_cgroup_namespaces(ns->ucounts);
+	put_user_ns(ns->user_ns);
+	ns_free_inum(&ns->ns);
+	kfree(ns);
+}
+EXPORT_SYMBOL(free_cgroup_ns);
+
+struct cgroup_namespace *copy_cgroup_ns(unsigned long flags,
+					struct user_namespace *user_ns,
+					struct cgroup_namespace *old_ns)
+{
+	struct cgroup_namespace *new_ns;
+	struct ucounts *ucounts;
+	struct css_set *cset;
+
+	BUG_ON(!old_ns);
+
+	if (!(flags & CLONE_NEWCGROUP)) {
+		get_cgroup_ns(old_ns);
+		return old_ns;
+	}
+
+	/* Allow only sysadmin to create cgroup namespace. */
+	if (!ns_capable(user_ns, CAP_SYS_ADMIN))
+		return ERR_PTR(-EPERM);
+
+	ucounts = inc_cgroup_namespaces(user_ns);
+	if (!ucounts)
+		return ERR_PTR(-ENOSPC);
+
+	/* It is not safe to take cgroup_mutex here */
+	spin_lock_irq(&css_set_lock);
+	cset = task_css_set(current);
+	get_css_set(cset);
+	spin_unlock_irq(&css_set_lock);
+
+	new_ns = alloc_cgroup_ns();
+	if (IS_ERR(new_ns)) {
+		put_css_set(cset);
+		dec_cgroup_namespaces(ucounts);
+		return new_ns;
+	}
+
+	new_ns->user_ns = get_user_ns(user_ns);
+	new_ns->ucounts = ucounts;
+	new_ns->root_cset = cset;
+
+	return new_ns;
+}
+
+static inline struct cgroup_namespace *to_cg_ns(struct ns_common *ns)
+{
+	return container_of(ns, struct cgroup_namespace, ns);
+}
+
+static int cgroupns_install(struct nsproxy *nsproxy, struct ns_common *ns)
+{
+	struct cgroup_namespace *cgroup_ns = to_cg_ns(ns);
+
+	if (!ns_capable(current_user_ns(), CAP_SYS_ADMIN) ||
+	    !ns_capable(cgroup_ns->user_ns, CAP_SYS_ADMIN))
+		return -EPERM;
+
+	/* Don't need to do anything if we are attaching to our own cgroupns. */
+	if (cgroup_ns == nsproxy->cgroup_ns)
+		return 0;
+
+	get_cgroup_ns(cgroup_ns);
+	put_cgroup_ns(nsproxy->cgroup_ns);
+	nsproxy->cgroup_ns = cgroup_ns;
+
+	return 0;
+}
+
+static struct ns_common *cgroupns_get(struct task_struct *task)
+{
+	struct cgroup_namespace *ns = NULL;
+	struct nsproxy *nsproxy;
+
+	task_lock(task);
+	nsproxy = task->nsproxy;
+	if (nsproxy) {
+		ns = nsproxy->cgroup_ns;
+		get_cgroup_ns(ns);
+	}
+	task_unlock(task);
+
+	return ns ? &ns->ns : NULL;
+}
+
+static void cgroupns_put(struct ns_common *ns)
+{
+	put_cgroup_ns(to_cg_ns(ns));
+}
+
+static struct user_namespace *cgroupns_owner(struct ns_common *ns)
+{
+	return to_cg_ns(ns)->user_ns;
+}
+
+const struct proc_ns_operations cgroupns_operations = {
+	.name		= "cgroup",
+	.type		= CLONE_NEWCGROUP,
+	.get		= cgroupns_get,
+	.put		= cgroupns_put,
+	.install	= cgroupns_install,
+	.owner		= cgroupns_owner,
+};
+
+static __init int cgroup_namespaces_init(void)
+{
+	return 0;
+}
+subsys_initcall(cgroup_namespaces_init);
diff --git a/kernel/cgroup/pids.c b/kernel/cgroup/pids.c
new file mode 100644
index 000000000..940d2e8db
--- /dev/null
+++ b/kernel/cgroup/pids.c
@@ -0,0 +1,350 @@
+/*
+ * Process number limiting controller for cgroups.
+ *
+ * Used to allow a cgroup hierarchy to stop any new processes from fork()ing
+ * after a certain limit is reached.
+ *
+ * Since it is trivial to hit the task limit without hitting any kmemcg limits
+ * in place, PIDs are a fundamental resource. As such, PID exhaustion must be
+ * preventable in the scope of a cgroup hierarchy by allowing resource limiting
+ * of the number of tasks in a cgroup.
+ *
+ * In order to use the `pids` controller, set the maximum number of tasks in
+ * pids.max (this is not available in the root cgroup for obvious reasons). The
+ * number of processes currently in the cgroup is given by pids.current.
+ * Organisational operations are not blocked by cgroup policies, so it is
+ * possible to have pids.current > pids.max. However, it is not possible to
+ * violate a cgroup policy through fork(). fork() will return -EAGAIN if forking
+ * would cause a cgroup policy to be violated.
+ *
+ * To set a cgroup to have no limit, set pids.max to "max". This is the default
+ * for all new cgroups (N.B. that PID limits are hierarchical, so the most
+ * stringent limit in the hierarchy is followed).
+ *
+ * pids.current tracks all child cgroup hierarchies, so parent/pids.current is
+ * a superset of parent/child/pids.current.
+ *
+ * Copyright (C) 2015 Aleksa Sarai <cyphar@cyphar.com>
+ *
+ * This file is subject to the terms and conditions of version 2 of the GNU
+ * General Public License.  See the file COPYING in the main directory of the
+ * Linux distribution for more details.
+ */
+
+#include <linux/kernel.h>
+#include <linux/threads.h>
+#include <linux/atomic.h>
+#include <linux/cgroup.h>
+#include <linux/slab.h>
+
+#define PIDS_MAX (PID_MAX_LIMIT + 1ULL)
+#define PIDS_MAX_STR "max"
+
+struct pids_cgroup {
+	struct cgroup_subsys_state	css;
+
+	/*
+	 * Use 64-bit types so that we can safely represent "max" as
+	 * %PIDS_MAX = (%PID_MAX_LIMIT + 1).
+	 */
+	atomic64_t			counter;
+	atomic64_t			limit;
+
+	/* Handle for "pids.events" */
+	struct cgroup_file		events_file;
+
+	/* Number of times fork failed because limit was hit. */
+	atomic64_t			events_limit;
+};
+
+static struct pids_cgroup *css_pids(struct cgroup_subsys_state *css)
+{
+	return container_of(css, struct pids_cgroup, css);
+}
+
+static struct pids_cgroup *parent_pids(struct pids_cgroup *pids)
+{
+	return css_pids(pids->css.parent);
+}
+
+static struct cgroup_subsys_state *
+pids_css_alloc(struct cgroup_subsys_state *parent)
+{
+	struct pids_cgroup *pids;
+
+	pids = kzalloc(sizeof(struct pids_cgroup), GFP_KERNEL);
+	if (!pids)
+		return ERR_PTR(-ENOMEM);
+
+	atomic64_set(&pids->counter, 0);
+	atomic64_set(&pids->limit, PIDS_MAX);
+	atomic64_set(&pids->events_limit, 0);
+	return &pids->css;
+}
+
+static void pids_css_free(struct cgroup_subsys_state *css)
+{
+	kfree(css_pids(css));
+}
+
+/**
+ * pids_cancel - uncharge the local pid count
+ * @pids: the pid cgroup state
+ * @num: the number of pids to cancel
+ *
+ * This function will WARN if the pid count goes under 0, because such a case is
+ * a bug in the pids controller proper.
+ */
+static void pids_cancel(struct pids_cgroup *pids, int num)
+{
+	/*
+	 * A negative count (or overflow for that matter) is invalid,
+	 * and indicates a bug in the `pids` controller proper.
+	 */
+	WARN_ON_ONCE(atomic64_add_negative(-num, &pids->counter));
+}
+
+/**
+ * pids_uncharge - hierarchically uncharge the pid count
+ * @pids: the pid cgroup state
+ * @num: the number of pids to uncharge
+ */
+static void pids_uncharge(struct pids_cgroup *pids, int num)
+{
+	struct pids_cgroup *p;
+
+	for (p = pids; parent_pids(p); p = parent_pids(p))
+		pids_cancel(p, num);
+}
+
+/**
+ * pids_charge - hierarchically charge the pid count
+ * @pids: the pid cgroup state
+ * @num: the number of pids to charge
+ *
+ * This function does *not* follow the pid limit set. It cannot fail and the new
+ * pid count may exceed the limit. This is only used for reverting failed
+ * attaches, where there is no other way out than violating the limit.
+ */
+static void pids_charge(struct pids_cgroup *pids, int num)
+{
+	struct pids_cgroup *p;
+
+	for (p = pids; parent_pids(p); p = parent_pids(p))
+		atomic64_add(num, &p->counter);
+}
+
+/**
+ * pids_try_charge - hierarchically try to charge the pid count
+ * @pids: the pid cgroup state
+ * @num: the number of pids to charge
+ *
+ * This function follows the set limit. It will fail if the charge would cause
+ * the new value to exceed the hierarchical limit. Returns 0 if the charge
+ * succeeded, otherwise -EAGAIN.
+ */
+static int pids_try_charge(struct pids_cgroup *pids, int num)
+{
+	struct pids_cgroup *p, *q;
+
+	for (p = pids; parent_pids(p); p = parent_pids(p)) {
+		int64_t new = atomic64_add_return(num, &p->counter);
+		int64_t limit = atomic64_read(&p->limit);
+
+		/*
+		 * Since new is capped to the maximum number of pid_t, if
+		 * p->limit is %PIDS_MAX then we know that this test will never
+		 * fail.
+		 */
+		if (new > limit)
+			goto revert;
+	}
+
+	return 0;
+
+revert:
+	for (q = pids; q != p; q = parent_pids(q))
+		pids_cancel(q, num);
+	pids_cancel(p, num);
+
+	return -EAGAIN;
+}
+
+static int pids_can_attach(struct cgroup_taskset *tset)
+{
+	struct task_struct *task;
+	struct cgroup_subsys_state *dst_css;
+
+	cgroup_taskset_for_each(task, dst_css, tset) {
+		struct pids_cgroup *pids = css_pids(dst_css);
+		struct cgroup_subsys_state *old_css;
+		struct pids_cgroup *old_pids;
+
+		/*
+		 * No need to pin @old_css between here and cancel_attach()
+		 * because cgroup core protects it from being freed before
+		 * the migration completes or fails.
+		 */
+		old_css = task_css(task, pids_cgrp_id);
+		old_pids = css_pids(old_css);
+
+		pids_charge(pids, 1);
+		pids_uncharge(old_pids, 1);
+	}
+
+	return 0;
+}
+
+static void pids_cancel_attach(struct cgroup_taskset *tset)
+{
+	struct task_struct *task;
+	struct cgroup_subsys_state *dst_css;
+
+	cgroup_taskset_for_each(task, dst_css, tset) {
+		struct pids_cgroup *pids = css_pids(dst_css);
+		struct cgroup_subsys_state *old_css;
+		struct pids_cgroup *old_pids;
+
+		old_css = task_css(task, pids_cgrp_id);
+		old_pids = css_pids(old_css);
+
+		pids_charge(old_pids, 1);
+		pids_uncharge(pids, 1);
+	}
+}
+
+/*
+ * task_css_check(true) in pids_can_fork() and pids_cancel_fork() relies
+ * on cgroup_threadgroup_change_begin() held by the copy_process().
+ */
+static int pids_can_fork(struct task_struct *task)
+{
+	struct cgroup_subsys_state *css;
+	struct pids_cgroup *pids;
+	int err;
+
+	css = task_css_check(current, pids_cgrp_id, true);
+	pids = css_pids(css);
+	err = pids_try_charge(pids, 1);
+	if (err) {
+		/* Only log the first time events_limit is incremented. */
+		if (atomic64_inc_return(&pids->events_limit) == 1) {
+			pr_info("cgroup: fork rejected by pids controller in ");
+			pr_cont_cgroup_path(css->cgroup);
+			pr_cont("\n");
+		}
+		cgroup_file_notify(&pids->events_file);
+	}
+	return err;
+}
+
+static void pids_cancel_fork(struct task_struct *task)
+{
+	struct cgroup_subsys_state *css;
+	struct pids_cgroup *pids;
+
+	css = task_css_check(current, pids_cgrp_id, true);
+	pids = css_pids(css);
+	pids_uncharge(pids, 1);
+}
+
+static void pids_release(struct task_struct *task)
+{
+	struct pids_cgroup *pids = css_pids(task_css(task, pids_cgrp_id));
+
+	pids_uncharge(pids, 1);
+}
+
+static ssize_t pids_max_write(struct kernfs_open_file *of, char *buf,
+			      size_t nbytes, loff_t off)
+{
+	struct cgroup_subsys_state *css = of_css(of);
+	struct pids_cgroup *pids = css_pids(css);
+	int64_t limit;
+	int err;
+
+	buf = strstrip(buf);
+	if (!strcmp(buf, PIDS_MAX_STR)) {
+		limit = PIDS_MAX;
+		goto set_limit;
+	}
+
+	err = kstrtoll(buf, 0, &limit);
+	if (err)
+		return err;
+
+	if (limit < 0 || limit >= PIDS_MAX)
+		return -EINVAL;
+
+set_limit:
+	/*
+	 * Limit updates don't need to be mutex'd, since it isn't
+	 * critical that any racing fork()s follow the new limit.
+	 */
+	atomic64_set(&pids->limit, limit);
+	return nbytes;
+}
+
+static int pids_max_show(struct seq_file *sf, void *v)
+{
+	struct cgroup_subsys_state *css = seq_css(sf);
+	struct pids_cgroup *pids = css_pids(css);
+	int64_t limit = atomic64_read(&pids->limit);
+
+	if (limit >= PIDS_MAX)
+		seq_printf(sf, "%s\n", PIDS_MAX_STR);
+	else
+		seq_printf(sf, "%lld\n", limit);
+
+	return 0;
+}
+
+static s64 pids_current_read(struct cgroup_subsys_state *css,
+			     struct cftype *cft)
+{
+	struct pids_cgroup *pids = css_pids(css);
+
+	return atomic64_read(&pids->counter);
+}
+
+static int pids_events_show(struct seq_file *sf, void *v)
+{
+	struct pids_cgroup *pids = css_pids(seq_css(sf));
+
+	seq_printf(sf, "max %lld\n", (s64)atomic64_read(&pids->events_limit));
+	return 0;
+}
+
+static struct cftype pids_files[] = {
+	{
+		.name = "max",
+		.write = pids_max_write,
+		.seq_show = pids_max_show,
+		.flags = CFTYPE_NOT_ON_ROOT,
+	},
+	{
+		.name = "current",
+		.read_s64 = pids_current_read,
+		.flags = CFTYPE_NOT_ON_ROOT,
+	},
+	{
+		.name = "events",
+		.seq_show = pids_events_show,
+		.file_offset = offsetof(struct pids_cgroup, events_file),
+		.flags = CFTYPE_NOT_ON_ROOT,
+	},
+	{ }	/* terminate */
+};
+
+struct cgroup_subsys pids_cgrp_subsys = {
+	.css_alloc	= pids_css_alloc,
+	.css_free	= pids_css_free,
+	.can_attach 	= pids_can_attach,
+	.cancel_attach 	= pids_cancel_attach,
+	.can_fork	= pids_can_fork,
+	.cancel_fork	= pids_cancel_fork,
+	.release	= pids_release,
+	.legacy_cftypes	= pids_files,
+	.dfl_cftypes	= pids_files,
+	.threaded	= true,
+};
diff --git a/kernel/cgroup/rdma.c b/kernel/cgroup/rdma.c
new file mode 100644
index 000000000..d3bbb757e
--- /dev/null
+++ b/kernel/cgroup/rdma.c
@@ -0,0 +1,616 @@
+/*
+ * RDMA resource limiting controller for cgroups.
+ *
+ * Used to allow a cgroup hierarchy to stop processes from consuming
+ * additional RDMA resources after a certain limit is reached.
+ *
+ * Copyright (C) 2016 Parav Pandit <pandit.parav@gmail.com>
+ *
+ * This file is subject to the terms and conditions of version 2 of the GNU
+ * General Public License. See the file COPYING in the main directory of the
+ * Linux distribution for more details.
+ */
+
+#include <linux/bitops.h>
+#include <linux/slab.h>
+#include <linux/seq_file.h>
+#include <linux/cgroup.h>
+#include <linux/parser.h>
+#include <linux/cgroup_rdma.h>
+
+#define RDMACG_MAX_STR "max"
+
+/*
+ * Protects list of resource pools maintained on per cgroup basis
+ * and rdma device list.
+ */
+static DEFINE_MUTEX(rdmacg_mutex);
+static LIST_HEAD(rdmacg_devices);
+
+enum rdmacg_file_type {
+	RDMACG_RESOURCE_TYPE_MAX,
+	RDMACG_RESOURCE_TYPE_STAT,
+};
+
+/*
+ * resource table definition as to be seen by the user.
+ * Need to add entries to it when more resources are
+ * added/defined at IB verb/core layer.
+ */
+static char const *rdmacg_resource_names[] = {
+	[RDMACG_RESOURCE_HCA_HANDLE]	= "hca_handle",
+	[RDMACG_RESOURCE_HCA_OBJECT]	= "hca_object",
+};
+
+/* resource tracker for each resource of rdma cgroup */
+struct rdmacg_resource {
+	int max;
+	int usage;
+};
+
+/*
+ * resource pool object which represents per cgroup, per device
+ * resources. There are multiple instances of this object per cgroup,
+ * therefore it cannot be embedded within rdma_cgroup structure. It
+ * is maintained as list.
+ */
+struct rdmacg_resource_pool {
+	struct rdmacg_device	*device;
+	struct rdmacg_resource	resources[RDMACG_RESOURCE_MAX];
+
+	struct list_head	cg_node;
+	struct list_head	dev_node;
+
+	/* count active user tasks of this pool */
+	u64			usage_sum;
+	/* total number counts which are set to max */
+	int			num_max_cnt;
+};
+
+static struct rdma_cgroup *css_rdmacg(struct cgroup_subsys_state *css)
+{
+	return container_of(css, struct rdma_cgroup, css);
+}
+
+static struct rdma_cgroup *parent_rdmacg(struct rdma_cgroup *cg)
+{
+	return css_rdmacg(cg->css.parent);
+}
+
+static inline struct rdma_cgroup *get_current_rdmacg(void)
+{
+	return css_rdmacg(task_get_css(current, rdma_cgrp_id));
+}
+
+static void set_resource_limit(struct rdmacg_resource_pool *rpool,
+			       int index, int new_max)
+{
+	if (new_max == S32_MAX) {
+		if (rpool->resources[index].max != S32_MAX)
+			rpool->num_max_cnt++;
+	} else {
+		if (rpool->resources[index].max == S32_MAX)
+			rpool->num_max_cnt--;
+	}
+	rpool->resources[index].max = new_max;
+}
+
+static void set_all_resource_max_limit(struct rdmacg_resource_pool *rpool)
+{
+	int i;
+
+	for (i = 0; i < RDMACG_RESOURCE_MAX; i++)
+		set_resource_limit(rpool, i, S32_MAX);
+}
+
+static void free_cg_rpool_locked(struct rdmacg_resource_pool *rpool)
+{
+	lockdep_assert_held(&rdmacg_mutex);
+
+	list_del(&rpool->cg_node);
+	list_del(&rpool->dev_node);
+	kfree(rpool);
+}
+
+static struct rdmacg_resource_pool *
+find_cg_rpool_locked(struct rdma_cgroup *cg,
+		     struct rdmacg_device *device)
+
+{
+	struct rdmacg_resource_pool *pool;
+
+	lockdep_assert_held(&rdmacg_mutex);
+
+	list_for_each_entry(pool, &cg->rpools, cg_node)
+		if (pool->device == device)
+			return pool;
+
+	return NULL;
+}
+
+static struct rdmacg_resource_pool *
+get_cg_rpool_locked(struct rdma_cgroup *cg, struct rdmacg_device *device)
+{
+	struct rdmacg_resource_pool *rpool;
+
+	rpool = find_cg_rpool_locked(cg, device);
+	if (rpool)
+		return rpool;
+
+	rpool = kzalloc(sizeof(*rpool), GFP_KERNEL);
+	if (!rpool)
+		return ERR_PTR(-ENOMEM);
+
+	rpool->device = device;
+	set_all_resource_max_limit(rpool);
+
+	INIT_LIST_HEAD(&rpool->cg_node);
+	INIT_LIST_HEAD(&rpool->dev_node);
+	list_add_tail(&rpool->cg_node, &cg->rpools);
+	list_add_tail(&rpool->dev_node, &device->rpools);
+	return rpool;
+}
+
+/**
+ * uncharge_cg_locked - uncharge resource for rdma cgroup
+ * @cg: pointer to cg to uncharge and all parents in hierarchy
+ * @device: pointer to rdmacg device
+ * @index: index of the resource to uncharge in cg (resource pool)
+ *
+ * It also frees the resource pool which was created as part of
+ * charging operation when there are no resources attached to
+ * resource pool.
+ */
+static void
+uncharge_cg_locked(struct rdma_cgroup *cg,
+		   struct rdmacg_device *device,
+		   enum rdmacg_resource_type index)
+{
+	struct rdmacg_resource_pool *rpool;
+
+	rpool = find_cg_rpool_locked(cg, device);
+
+	/*
+	 * rpool cannot be null at this stage. Let kernel operate in case
+	 * if there a bug in IB stack or rdma controller, instead of crashing
+	 * the system.
+	 */
+	if (unlikely(!rpool)) {
+		pr_warn("Invalid device %p or rdma cgroup %p\n", cg, device);
+		return;
+	}
+
+	rpool->resources[index].usage--;
+
+	/*
+	 * A negative count (or overflow) is invalid,
+	 * it indicates a bug in the rdma controller.
+	 */
+	WARN_ON_ONCE(rpool->resources[index].usage < 0);
+	rpool->usage_sum--;
+	if (rpool->usage_sum == 0 &&
+	    rpool->num_max_cnt == RDMACG_RESOURCE_MAX) {
+		/*
+		 * No user of the rpool and all entries are set to max, so
+		 * safe to delete this rpool.
+		 */
+		free_cg_rpool_locked(rpool);
+	}
+}
+
+/**
+ * rdmacg_uncharge_hierarchy - hierarchically uncharge rdma resource count
+ * @device: pointer to rdmacg device
+ * @stop_cg: while traversing hirerchy, when meet with stop_cg cgroup
+ *           stop uncharging
+ * @index: index of the resource to uncharge in cg in given resource pool
+ */
+static void rdmacg_uncharge_hierarchy(struct rdma_cgroup *cg,
+				     struct rdmacg_device *device,
+				     struct rdma_cgroup *stop_cg,
+				     enum rdmacg_resource_type index)
+{
+	struct rdma_cgroup *p;
+
+	mutex_lock(&rdmacg_mutex);
+
+	for (p = cg; p != stop_cg; p = parent_rdmacg(p))
+		uncharge_cg_locked(p, device, index);
+
+	mutex_unlock(&rdmacg_mutex);
+
+	css_put(&cg->css);
+}
+
+/**
+ * rdmacg_uncharge - hierarchically uncharge rdma resource count
+ * @device: pointer to rdmacg device
+ * @index: index of the resource to uncharge in cgroup in given resource pool
+ */
+void rdmacg_uncharge(struct rdma_cgroup *cg,
+		     struct rdmacg_device *device,
+		     enum rdmacg_resource_type index)
+{
+	if (index >= RDMACG_RESOURCE_MAX)
+		return;
+
+	rdmacg_uncharge_hierarchy(cg, device, NULL, index);
+}
+EXPORT_SYMBOL(rdmacg_uncharge);
+
+/**
+ * rdmacg_try_charge - hierarchically try to charge the rdma resource
+ * @rdmacg: pointer to rdma cgroup which will own this resource
+ * @device: pointer to rdmacg device
+ * @index: index of the resource to charge in cgroup (resource pool)
+ *
+ * This function follows charging resource in hierarchical way.
+ * It will fail if the charge would cause the new value to exceed the
+ * hierarchical limit.
+ * Returns 0 if the charge succeded, otherwise -EAGAIN, -ENOMEM or -EINVAL.
+ * Returns pointer to rdmacg for this resource when charging is successful.
+ *
+ * Charger needs to account resources on two criteria.
+ * (a) per cgroup & (b) per device resource usage.
+ * Per cgroup resource usage ensures that tasks of cgroup doesn't cross
+ * the configured limits. Per device provides granular configuration
+ * in multi device usage. It allocates resource pool in the hierarchy
+ * for each parent it come across for first resource. Later on resource
+ * pool will be available. Therefore it will be much faster thereon
+ * to charge/uncharge.
+ */
+int rdmacg_try_charge(struct rdma_cgroup **rdmacg,
+		      struct rdmacg_device *device,
+		      enum rdmacg_resource_type index)
+{
+	struct rdma_cgroup *cg, *p;
+	struct rdmacg_resource_pool *rpool;
+	s64 new;
+	int ret = 0;
+
+	if (index >= RDMACG_RESOURCE_MAX)
+		return -EINVAL;
+
+	/*
+	 * hold on to css, as cgroup can be removed but resource
+	 * accounting happens on css.
+	 */
+	cg = get_current_rdmacg();
+
+	mutex_lock(&rdmacg_mutex);
+	for (p = cg; p; p = parent_rdmacg(p)) {
+		rpool = get_cg_rpool_locked(p, device);
+		if (IS_ERR(rpool)) {
+			ret = PTR_ERR(rpool);
+			goto err;
+		} else {
+			new = rpool->resources[index].usage + 1;
+			if (new > rpool->resources[index].max) {
+				ret = -EAGAIN;
+				goto err;
+			} else {
+				rpool->resources[index].usage = new;
+				rpool->usage_sum++;
+			}
+		}
+	}
+	mutex_unlock(&rdmacg_mutex);
+
+	*rdmacg = cg;
+	return 0;
+
+err:
+	mutex_unlock(&rdmacg_mutex);
+	rdmacg_uncharge_hierarchy(cg, device, p, index);
+	return ret;
+}
+EXPORT_SYMBOL(rdmacg_try_charge);
+
+/**
+ * rdmacg_register_device - register rdmacg device to rdma controller.
+ * @device: pointer to rdmacg device whose resources need to be accounted.
+ *
+ * If IB stack wish a device to participate in rdma cgroup resource
+ * tracking, it must invoke this API to register with rdma cgroup before
+ * any user space application can start using the RDMA resources.
+ * Returns 0 on success or EINVAL when table length given is beyond
+ * supported size.
+ */
+int rdmacg_register_device(struct rdmacg_device *device)
+{
+	INIT_LIST_HEAD(&device->dev_node);
+	INIT_LIST_HEAD(&device->rpools);
+
+	mutex_lock(&rdmacg_mutex);
+	list_add_tail(&device->dev_node, &rdmacg_devices);
+	mutex_unlock(&rdmacg_mutex);
+	return 0;
+}
+EXPORT_SYMBOL(rdmacg_register_device);
+
+/**
+ * rdmacg_unregister_device - unregister rdmacg device from rdma controller.
+ * @device: pointer to rdmacg device which was previously registered with rdma
+ *          controller using rdmacg_register_device().
+ *
+ * IB stack must invoke this after all the resources of the IB device
+ * are destroyed and after ensuring that no more resources will be created
+ * when this API is invoked.
+ */
+void rdmacg_unregister_device(struct rdmacg_device *device)
+{
+	struct rdmacg_resource_pool *rpool, *tmp;
+
+	/*
+	 * Synchronize with any active resource settings,
+	 * usage query happening via configfs.
+	 */
+	mutex_lock(&rdmacg_mutex);
+	list_del_init(&device->dev_node);
+
+	/*
+	 * Now that this device is off the cgroup list, its safe to free
+	 * all the rpool resources.
+	 */
+	list_for_each_entry_safe(rpool, tmp, &device->rpools, dev_node)
+		free_cg_rpool_locked(rpool);
+
+	mutex_unlock(&rdmacg_mutex);
+}
+EXPORT_SYMBOL(rdmacg_unregister_device);
+
+static int parse_resource(char *c, int *intval)
+{
+	substring_t argstr;
+	char *name, *value = c;
+	size_t len;
+	int ret, i;
+
+	name = strsep(&value, "=");
+	if (!name || !value)
+		return -EINVAL;
+
+	i = match_string(rdmacg_resource_names, RDMACG_RESOURCE_MAX, name);
+	if (i < 0)
+		return i;
+
+	len = strlen(value);
+
+	argstr.from = value;
+	argstr.to = value + len;
+
+	ret = match_int(&argstr, intval);
+	if (ret >= 0) {
+		if (*intval < 0)
+			return -EINVAL;
+		return i;
+	}
+	if (strncmp(value, RDMACG_MAX_STR, len) == 0) {
+		*intval = S32_MAX;
+		return i;
+	}
+	return -EINVAL;
+}
+
+static int rdmacg_parse_limits(char *options,
+			       int *new_limits, unsigned long *enables)
+{
+	char *c;
+	int err = -EINVAL;
+
+	/* parse resource options */
+	while ((c = strsep(&options, " ")) != NULL) {
+		int index, intval;
+
+		index = parse_resource(c, &intval);
+		if (index < 0)
+			goto err;
+
+		new_limits[index] = intval;
+		*enables |= BIT(index);
+	}
+	return 0;
+
+err:
+	return err;
+}
+
+static struct rdmacg_device *rdmacg_get_device_locked(const char *name)
+{
+	struct rdmacg_device *device;
+
+	lockdep_assert_held(&rdmacg_mutex);
+
+	list_for_each_entry(device, &rdmacg_devices, dev_node)
+		if (!strcmp(name, device->name))
+			return device;
+
+	return NULL;
+}
+
+static ssize_t rdmacg_resource_set_max(struct kernfs_open_file *of,
+				       char *buf, size_t nbytes, loff_t off)
+{
+	struct rdma_cgroup *cg = css_rdmacg(of_css(of));
+	const char *dev_name;
+	struct rdmacg_resource_pool *rpool;
+	struct rdmacg_device *device;
+	char *options = strstrip(buf);
+	int *new_limits;
+	unsigned long enables = 0;
+	int i = 0, ret = 0;
+
+	/* extract the device name first */
+	dev_name = strsep(&options, " ");
+	if (!dev_name) {
+		ret = -EINVAL;
+		goto err;
+	}
+
+	new_limits = kcalloc(RDMACG_RESOURCE_MAX, sizeof(int), GFP_KERNEL);
+	if (!new_limits) {
+		ret = -ENOMEM;
+		goto err;
+	}
+
+	ret = rdmacg_parse_limits(options, new_limits, &enables);
+	if (ret)
+		goto parse_err;
+
+	/* acquire lock to synchronize with hot plug devices */
+	mutex_lock(&rdmacg_mutex);
+
+	device = rdmacg_get_device_locked(dev_name);
+	if (!device) {
+		ret = -ENODEV;
+		goto dev_err;
+	}
+
+	rpool = get_cg_rpool_locked(cg, device);
+	if (IS_ERR(rpool)) {
+		ret = PTR_ERR(rpool);
+		goto dev_err;
+	}
+
+	/* now set the new limits of the rpool */
+	for_each_set_bit(i, &enables, RDMACG_RESOURCE_MAX)
+		set_resource_limit(rpool, i, new_limits[i]);
+
+	if (rpool->usage_sum == 0 &&
+	    rpool->num_max_cnt == RDMACG_RESOURCE_MAX) {
+		/*
+		 * No user of the rpool and all entries are set to max, so
+		 * safe to delete this rpool.
+		 */
+		free_cg_rpool_locked(rpool);
+	}
+
+dev_err:
+	mutex_unlock(&rdmacg_mutex);
+
+parse_err:
+	kfree(new_limits);
+
+err:
+	return ret ?: nbytes;
+}
+
+static void print_rpool_values(struct seq_file *sf,
+			       struct rdmacg_resource_pool *rpool)
+{
+	enum rdmacg_file_type sf_type;
+	int i;
+	u32 value;
+
+	sf_type = seq_cft(sf)->private;
+
+	for (i = 0; i < RDMACG_RESOURCE_MAX; i++) {
+		seq_puts(sf, rdmacg_resource_names[i]);
+		seq_putc(sf, '=');
+		if (sf_type == RDMACG_RESOURCE_TYPE_MAX) {
+			if (rpool)
+				value = rpool->resources[i].max;
+			else
+				value = S32_MAX;
+		} else {
+			if (rpool)
+				value = rpool->resources[i].usage;
+			else
+				value = 0;
+		}
+
+		if (value == S32_MAX)
+			seq_puts(sf, RDMACG_MAX_STR);
+		else
+			seq_printf(sf, "%d", value);
+		seq_putc(sf, ' ');
+	}
+}
+
+static int rdmacg_resource_read(struct seq_file *sf, void *v)
+{
+	struct rdmacg_device *device;
+	struct rdmacg_resource_pool *rpool;
+	struct rdma_cgroup *cg = css_rdmacg(seq_css(sf));
+
+	mutex_lock(&rdmacg_mutex);
+
+	list_for_each_entry(device, &rdmacg_devices, dev_node) {
+		seq_printf(sf, "%s ", device->name);
+
+		rpool = find_cg_rpool_locked(cg, device);
+		print_rpool_values(sf, rpool);
+
+		seq_putc(sf, '\n');
+	}
+
+	mutex_unlock(&rdmacg_mutex);
+	return 0;
+}
+
+static struct cftype rdmacg_files[] = {
+	{
+		.name = "max",
+		.write = rdmacg_resource_set_max,
+		.seq_show = rdmacg_resource_read,
+		.private = RDMACG_RESOURCE_TYPE_MAX,
+		.flags = CFTYPE_NOT_ON_ROOT,
+	},
+	{
+		.name = "current",
+		.seq_show = rdmacg_resource_read,
+		.private = RDMACG_RESOURCE_TYPE_STAT,
+		.flags = CFTYPE_NOT_ON_ROOT,
+	},
+	{ }	/* terminate */
+};
+
+static struct cgroup_subsys_state *
+rdmacg_css_alloc(struct cgroup_subsys_state *parent)
+{
+	struct rdma_cgroup *cg;
+
+	cg = kzalloc(sizeof(*cg), GFP_KERNEL);
+	if (!cg)
+		return ERR_PTR(-ENOMEM);
+
+	INIT_LIST_HEAD(&cg->rpools);
+	return &cg->css;
+}
+
+static void rdmacg_css_free(struct cgroup_subsys_state *css)
+{
+	struct rdma_cgroup *cg = css_rdmacg(css);
+
+	kfree(cg);
+}
+
+/**
+ * rdmacg_css_offline - cgroup css_offline callback
+ * @css: css of interest
+ *
+ * This function is called when @css is about to go away and responsible
+ * for shooting down all rdmacg associated with @css. As part of that it
+ * marks all the resource pool entries to max value, so that when resources are
+ * uncharged, associated resource pool can be freed as well.
+ */
+static void rdmacg_css_offline(struct cgroup_subsys_state *css)
+{
+	struct rdma_cgroup *cg = css_rdmacg(css);
+	struct rdmacg_resource_pool *rpool;
+
+	mutex_lock(&rdmacg_mutex);
+
+	list_for_each_entry(rpool, &cg->rpools, cg_node)
+		set_all_resource_max_limit(rpool);
+
+	mutex_unlock(&rdmacg_mutex);
+}
+
+struct cgroup_subsys rdma_cgrp_subsys = {
+	.css_alloc	= rdmacg_css_alloc,
+	.css_free	= rdmacg_css_free,
+	.css_offline	= rdmacg_css_offline,
+	.legacy_cftypes	= rdmacg_files,
+	.dfl_cftypes	= rdmacg_files,
+};
diff --git a/kernel/cgroup/rstat.c b/kernel/cgroup/rstat.c
new file mode 100644
index 000000000..d0ed410b4
--- /dev/null
+++ b/kernel/cgroup/rstat.c
@@ -0,0 +1,408 @@
+#include "cgroup-internal.h"
+
+#include <linux/sched/cputime.h>
+
+static DEFINE_SPINLOCK(cgroup_rstat_lock);
+static DEFINE_PER_CPU(raw_spinlock_t, cgroup_rstat_cpu_lock);
+
+static void cgroup_base_stat_flush(struct cgroup *cgrp, int cpu);
+
+static struct cgroup_rstat_cpu *cgroup_rstat_cpu(struct cgroup *cgrp, int cpu)
+{
+	return per_cpu_ptr(cgrp->rstat_cpu, cpu);
+}
+
+/**
+ * cgroup_rstat_updated - keep track of updated rstat_cpu
+ * @cgrp: target cgroup
+ * @cpu: cpu on which rstat_cpu was updated
+ *
+ * @cgrp's rstat_cpu on @cpu was updated.  Put it on the parent's matching
+ * rstat_cpu->updated_children list.  See the comment on top of
+ * cgroup_rstat_cpu definition for details.
+ */
+void cgroup_rstat_updated(struct cgroup *cgrp, int cpu)
+{
+	raw_spinlock_t *cpu_lock = per_cpu_ptr(&cgroup_rstat_cpu_lock, cpu);
+	struct cgroup *parent;
+	unsigned long flags;
+
+	/* nothing to do for root */
+	if (!cgroup_parent(cgrp))
+		return;
+
+	/*
+	 * Speculative already-on-list test. This may race leading to
+	 * temporary inaccuracies, which is fine.
+	 *
+	 * Because @parent's updated_children is terminated with @parent
+	 * instead of NULL, we can tell whether @cgrp is on the list by
+	 * testing the next pointer for NULL.
+	 */
+	if (cgroup_rstat_cpu(cgrp, cpu)->updated_next)
+		return;
+
+	raw_spin_lock_irqsave(cpu_lock, flags);
+
+	/* put @cgrp and all ancestors on the corresponding updated lists */
+	for (parent = cgroup_parent(cgrp); parent;
+	     cgrp = parent, parent = cgroup_parent(cgrp)) {
+		struct cgroup_rstat_cpu *rstatc = cgroup_rstat_cpu(cgrp, cpu);
+		struct cgroup_rstat_cpu *prstatc = cgroup_rstat_cpu(parent, cpu);
+
+		/*
+		 * Both additions and removals are bottom-up.  If a cgroup
+		 * is already in the tree, all ancestors are.
+		 */
+		if (rstatc->updated_next)
+			break;
+
+		rstatc->updated_next = prstatc->updated_children;
+		prstatc->updated_children = cgrp;
+	}
+
+	raw_spin_unlock_irqrestore(cpu_lock, flags);
+}
+EXPORT_SYMBOL_GPL(cgroup_rstat_updated);
+
+/**
+ * cgroup_rstat_cpu_pop_updated - iterate and dismantle rstat_cpu updated tree
+ * @pos: current position
+ * @root: root of the tree to traversal
+ * @cpu: target cpu
+ *
+ * Walks the udpated rstat_cpu tree on @cpu from @root.  %NULL @pos starts
+ * the traversal and %NULL return indicates the end.  During traversal,
+ * each returned cgroup is unlinked from the tree.  Must be called with the
+ * matching cgroup_rstat_cpu_lock held.
+ *
+ * The only ordering guarantee is that, for a parent and a child pair
+ * covered by a given traversal, if a child is visited, its parent is
+ * guaranteed to be visited afterwards.
+ */
+static struct cgroup *cgroup_rstat_cpu_pop_updated(struct cgroup *pos,
+						   struct cgroup *root, int cpu)
+{
+	struct cgroup_rstat_cpu *rstatc;
+
+	if (pos == root)
+		return NULL;
+
+	/*
+	 * We're gonna walk down to the first leaf and visit/remove it.  We
+	 * can pick whatever unvisited node as the starting point.
+	 */
+	if (!pos)
+		pos = root;
+	else
+		pos = cgroup_parent(pos);
+
+	/* walk down to the first leaf */
+	while (true) {
+		rstatc = cgroup_rstat_cpu(pos, cpu);
+		if (rstatc->updated_children == pos)
+			break;
+		pos = rstatc->updated_children;
+	}
+
+	/*
+	 * Unlink @pos from the tree.  As the updated_children list is
+	 * singly linked, we have to walk it to find the removal point.
+	 * However, due to the way we traverse, @pos will be the first
+	 * child in most cases. The only exception is @root.
+	 */
+	if (rstatc->updated_next) {
+		struct cgroup *parent = cgroup_parent(pos);
+		struct cgroup_rstat_cpu *prstatc = cgroup_rstat_cpu(parent, cpu);
+		struct cgroup_rstat_cpu *nrstatc;
+		struct cgroup **nextp;
+
+		nextp = &prstatc->updated_children;
+		while (true) {
+			nrstatc = cgroup_rstat_cpu(*nextp, cpu);
+			if (*nextp == pos)
+				break;
+
+			WARN_ON_ONCE(*nextp == parent);
+			nextp = &nrstatc->updated_next;
+		}
+
+		*nextp = rstatc->updated_next;
+		rstatc->updated_next = NULL;
+
+		return pos;
+	}
+
+	/* only happens for @root */
+	return NULL;
+}
+
+/* see cgroup_rstat_flush() */
+static void cgroup_rstat_flush_locked(struct cgroup *cgrp, bool may_sleep)
+	__releases(&cgroup_rstat_lock) __acquires(&cgroup_rstat_lock)
+{
+	int cpu;
+
+	lockdep_assert_held(&cgroup_rstat_lock);
+
+	for_each_possible_cpu(cpu) {
+		raw_spinlock_t *cpu_lock = per_cpu_ptr(&cgroup_rstat_cpu_lock,
+						       cpu);
+		struct cgroup *pos = NULL;
+
+		raw_spin_lock(cpu_lock);
+		while ((pos = cgroup_rstat_cpu_pop_updated(pos, cgrp, cpu))) {
+			struct cgroup_subsys_state *css;
+
+			cgroup_base_stat_flush(pos, cpu);
+
+			rcu_read_lock();
+			list_for_each_entry_rcu(css, &pos->rstat_css_list,
+						rstat_css_node)
+				css->ss->css_rstat_flush(css, cpu);
+			rcu_read_unlock();
+		}
+		raw_spin_unlock(cpu_lock);
+
+		/* if @may_sleep, play nice and yield if necessary */
+		if (may_sleep && (need_resched() ||
+				  spin_needbreak(&cgroup_rstat_lock))) {
+			spin_unlock_irq(&cgroup_rstat_lock);
+			if (!cond_resched())
+				cpu_relax();
+			spin_lock_irq(&cgroup_rstat_lock);
+		}
+	}
+}
+
+/**
+ * cgroup_rstat_flush - flush stats in @cgrp's subtree
+ * @cgrp: target cgroup
+ *
+ * Collect all per-cpu stats in @cgrp's subtree into the global counters
+ * and propagate them upwards.  After this function returns, all cgroups in
+ * the subtree have up-to-date ->stat.
+ *
+ * This also gets all cgroups in the subtree including @cgrp off the
+ * ->updated_children lists.
+ *
+ * This function may block.
+ */
+void cgroup_rstat_flush(struct cgroup *cgrp)
+{
+	might_sleep();
+
+	spin_lock_irq(&cgroup_rstat_lock);
+	cgroup_rstat_flush_locked(cgrp, true);
+	spin_unlock_irq(&cgroup_rstat_lock);
+}
+
+/**
+ * cgroup_rstat_flush_irqsafe - irqsafe version of cgroup_rstat_flush()
+ * @cgrp: target cgroup
+ *
+ * This function can be called from any context.
+ */
+void cgroup_rstat_flush_irqsafe(struct cgroup *cgrp)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&cgroup_rstat_lock, flags);
+	cgroup_rstat_flush_locked(cgrp, false);
+	spin_unlock_irqrestore(&cgroup_rstat_lock, flags);
+}
+
+/**
+ * cgroup_rstat_flush_begin - flush stats in @cgrp's subtree and hold
+ * @cgrp: target cgroup
+ *
+ * Flush stats in @cgrp's subtree and prevent further flushes.  Must be
+ * paired with cgroup_rstat_flush_release().
+ *
+ * This function may block.
+ */
+void cgroup_rstat_flush_hold(struct cgroup *cgrp)
+	__acquires(&cgroup_rstat_lock)
+{
+	might_sleep();
+	spin_lock_irq(&cgroup_rstat_lock);
+	cgroup_rstat_flush_locked(cgrp, true);
+}
+
+/**
+ * cgroup_rstat_flush_release - release cgroup_rstat_flush_hold()
+ */
+void cgroup_rstat_flush_release(void)
+	__releases(&cgroup_rstat_lock)
+{
+	spin_unlock_irq(&cgroup_rstat_lock);
+}
+
+int cgroup_rstat_init(struct cgroup *cgrp)
+{
+	int cpu;
+
+	/* the root cgrp has rstat_cpu preallocated */
+	if (!cgrp->rstat_cpu) {
+		cgrp->rstat_cpu = alloc_percpu(struct cgroup_rstat_cpu);
+		if (!cgrp->rstat_cpu)
+			return -ENOMEM;
+	}
+
+	/* ->updated_children list is self terminated */
+	for_each_possible_cpu(cpu) {
+		struct cgroup_rstat_cpu *rstatc = cgroup_rstat_cpu(cgrp, cpu);
+
+		rstatc->updated_children = cgrp;
+		u64_stats_init(&rstatc->bsync);
+	}
+
+	return 0;
+}
+
+void cgroup_rstat_exit(struct cgroup *cgrp)
+{
+	int cpu;
+
+	cgroup_rstat_flush(cgrp);
+
+	/* sanity check */
+	for_each_possible_cpu(cpu) {
+		struct cgroup_rstat_cpu *rstatc = cgroup_rstat_cpu(cgrp, cpu);
+
+		if (WARN_ON_ONCE(rstatc->updated_children != cgrp) ||
+		    WARN_ON_ONCE(rstatc->updated_next))
+			return;
+	}
+
+	free_percpu(cgrp->rstat_cpu);
+	cgrp->rstat_cpu = NULL;
+}
+
+void __init cgroup_rstat_boot(void)
+{
+	int cpu;
+
+	for_each_possible_cpu(cpu)
+		raw_spin_lock_init(per_cpu_ptr(&cgroup_rstat_cpu_lock, cpu));
+
+	BUG_ON(cgroup_rstat_init(&cgrp_dfl_root.cgrp));
+}
+
+/*
+ * Functions for cgroup basic resource statistics implemented on top of
+ * rstat.
+ */
+static void cgroup_base_stat_accumulate(struct cgroup_base_stat *dst_bstat,
+					struct cgroup_base_stat *src_bstat)
+{
+	dst_bstat->cputime.utime += src_bstat->cputime.utime;
+	dst_bstat->cputime.stime += src_bstat->cputime.stime;
+	dst_bstat->cputime.sum_exec_runtime += src_bstat->cputime.sum_exec_runtime;
+}
+
+static void cgroup_base_stat_flush(struct cgroup *cgrp, int cpu)
+{
+	struct cgroup *parent = cgroup_parent(cgrp);
+	struct cgroup_rstat_cpu *rstatc = cgroup_rstat_cpu(cgrp, cpu);
+	struct task_cputime *last_cputime = &rstatc->last_bstat.cputime;
+	struct task_cputime cputime;
+	struct cgroup_base_stat delta;
+	unsigned seq;
+
+	/* fetch the current per-cpu values */
+	do {
+		seq = __u64_stats_fetch_begin(&rstatc->bsync);
+		cputime = rstatc->bstat.cputime;
+	} while (__u64_stats_fetch_retry(&rstatc->bsync, seq));
+
+	/* calculate the delta to propgate */
+	delta.cputime.utime = cputime.utime - last_cputime->utime;
+	delta.cputime.stime = cputime.stime - last_cputime->stime;
+	delta.cputime.sum_exec_runtime = cputime.sum_exec_runtime -
+					 last_cputime->sum_exec_runtime;
+	*last_cputime = cputime;
+
+	/* transfer the pending stat into delta */
+	cgroup_base_stat_accumulate(&delta, &cgrp->pending_bstat);
+	memset(&cgrp->pending_bstat, 0, sizeof(cgrp->pending_bstat));
+
+	/* propagate delta into the global stat and the parent's pending */
+	cgroup_base_stat_accumulate(&cgrp->bstat, &delta);
+	if (parent)
+		cgroup_base_stat_accumulate(&parent->pending_bstat, &delta);
+}
+
+static struct cgroup_rstat_cpu *
+cgroup_base_stat_cputime_account_begin(struct cgroup *cgrp)
+{
+	struct cgroup_rstat_cpu *rstatc;
+
+	rstatc = get_cpu_ptr(cgrp->rstat_cpu);
+	u64_stats_update_begin(&rstatc->bsync);
+	return rstatc;
+}
+
+static void cgroup_base_stat_cputime_account_end(struct cgroup *cgrp,
+						 struct cgroup_rstat_cpu *rstatc)
+{
+	u64_stats_update_end(&rstatc->bsync);
+	cgroup_rstat_updated(cgrp, smp_processor_id());
+	put_cpu_ptr(rstatc);
+}
+
+void __cgroup_account_cputime(struct cgroup *cgrp, u64 delta_exec)
+{
+	struct cgroup_rstat_cpu *rstatc;
+
+	rstatc = cgroup_base_stat_cputime_account_begin(cgrp);
+	rstatc->bstat.cputime.sum_exec_runtime += delta_exec;
+	cgroup_base_stat_cputime_account_end(cgrp, rstatc);
+}
+
+void __cgroup_account_cputime_field(struct cgroup *cgrp,
+				    enum cpu_usage_stat index, u64 delta_exec)
+{
+	struct cgroup_rstat_cpu *rstatc;
+
+	rstatc = cgroup_base_stat_cputime_account_begin(cgrp);
+
+	switch (index) {
+	case CPUTIME_USER:
+	case CPUTIME_NICE:
+		rstatc->bstat.cputime.utime += delta_exec;
+		break;
+	case CPUTIME_SYSTEM:
+	case CPUTIME_IRQ:
+	case CPUTIME_SOFTIRQ:
+		rstatc->bstat.cputime.stime += delta_exec;
+		break;
+	default:
+		break;
+	}
+
+	cgroup_base_stat_cputime_account_end(cgrp, rstatc);
+}
+
+void cgroup_base_stat_cputime_show(struct seq_file *seq)
+{
+	struct cgroup *cgrp = seq_css(seq)->cgroup;
+	u64 usage, utime, stime;
+
+	if (!cgroup_parent(cgrp))
+		return;
+
+	cgroup_rstat_flush_hold(cgrp);
+	usage = cgrp->bstat.cputime.sum_exec_runtime;
+	cputime_adjust(&cgrp->bstat.cputime, &cgrp->prev_cputime, &utime, &stime);
+	cgroup_rstat_flush_release();
+
+	do_div(usage, NSEC_PER_USEC);
+	do_div(utime, NSEC_PER_USEC);
+	do_div(stime, NSEC_PER_USEC);
+
+	seq_printf(seq, "usage_usec %llu\n"
+		   "user_usec %llu\n"
+		   "system_usec %llu\n",
+		   usage, utime, stime);
+}