Adding upstream version 6.6.15.upstream/6.6.15

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

1 files changed, 4321 insertions, 0 deletions

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
new file mode 100644
index 0000000000..4749e0c86c
--- /dev/null
+++ b/kernel/cgroup/cpuset.c
@@ -0,0 +1,4321 @@
+/*
+ *  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/init.h>
+#include <linux/interrupt.h>
+#include <linux/kernel.h>
+#include <linux/mempolicy.h>
+#include <linux/mm.h>
+#include <linux/memory.h>
+#include <linux/export.h>
+#include <linux/rcupdate.h>
+#include <linux/sched.h>
+#include <linux/sched/deadline.h>
+#include <linux/sched/mm.h>
+#include <linux/sched/task.h>
+#include <linux/security.h>
+#include <linux/spinlock.h>
+#include <linux/oom.h>
+#include <linux/sched/isolation.h>
+#include <linux/cgroup.h>
+#include <linux/wait.h>
+
+DEFINE_STATIC_KEY_FALSE(cpusets_pre_enable_key);
+DEFINE_STATIC_KEY_FALSE(cpusets_enabled_key);
+
+/*
+ * There could be abnormal cpuset configurations for cpu or memory
+ * node binding, add this key to provide a quick low-cost judgment
+ * of the situation.
+ */
+DEFINE_STATIC_KEY_FALSE(cpusets_insane_config_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 */
+};
+
+/*
+ * Invalid partition error code
+ */
+enum prs_errcode {
+	PERR_NONE = 0,
+	PERR_INVCPUS,
+	PERR_INVPARENT,
+	PERR_NOTPART,
+	PERR_NOTEXCL,
+	PERR_NOCPUS,
+	PERR_HOTPLUG,
+	PERR_CPUSEMPTY,
+};
+
+static const char * const perr_strings[] = {
+	[PERR_INVCPUS]   = "Invalid cpu list in cpuset.cpus",
+	[PERR_INVPARENT] = "Parent is an invalid partition root",
+	[PERR_NOTPART]   = "Parent is not a partition root",
+	[PERR_NOTEXCL]   = "Cpu list in cpuset.cpus not exclusive",
+	[PERR_NOCPUS]    = "Parent unable to distribute cpu downstream",
+	[PERR_HOTPLUG]   = "No cpu available due to hotplug",
+	[PERR_CPUSEMPTY] = "cpuset.cpus is empty",
+};
+
+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 hierarchy:
+	 *
+	 * 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;
+
+	/*
+	 * CPUs allocated to child sub-partitions (default hierarchy only)
+	 * - CPUs granted by the parent = effective_cpus U subparts_cpus
+	 * - effective_cpus and subparts_cpus are mutually exclusive.
+	 *
+	 * effective_cpus contains only onlined CPUs, but subparts_cpus
+	 * may have offlined ones.
+	 */
+	cpumask_var_t subparts_cpus;
+
+	/*
+	 * 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;
+
+	/* number of CPUs in subparts_cpus */
+	int nr_subparts_cpus;
+
+	/* partition root state */
+	int partition_root_state;
+
+	/*
+	 * Default hierarchy only:
+	 * use_parent_ecpus - set if using parent's effective_cpus
+	 * child_ecpus_count - # of children with use_parent_ecpus set
+	 */
+	int use_parent_ecpus;
+	int child_ecpus_count;
+
+	/*
+	 * number of SCHED_DEADLINE tasks attached to this cpuset, so that we
+	 * know when to rebuild associated root domain bandwidth information.
+	 */
+	int nr_deadline_tasks;
+	int nr_migrate_dl_tasks;
+	u64 sum_migrate_dl_bw;
+
+	/* Invalid partition error code, not lock protected */
+	enum prs_errcode prs_err;
+
+	/* Handle for cpuset.cpus.partition */
+	struct cgroup_file partition_file;
+};
+
+/*
+ * Partition root states:
+ *
+ *   0 - member (not a partition root)
+ *   1 - partition root
+ *   2 - partition root without load balancing (isolated)
+ *  -1 - invalid partition root
+ *  -2 - invalid isolated partition root
+ */
+#define PRS_MEMBER		0
+#define PRS_ROOT		1
+#define PRS_ISOLATED		2
+#define PRS_INVALID_ROOT	-1
+#define PRS_INVALID_ISOLATED	-2
+
+static inline bool is_prs_invalid(int prs_state)
+{
+	return prs_state < 0;
+}
+
+/*
+ * Temporary cpumasks for working with partitions that are passed among
+ * functions to avoid memory allocation in inner functions.
+ */
+struct tmpmasks {
+	cpumask_var_t addmask, delmask;	/* For partition root */
+	cpumask_var_t new_cpus;		/* For update_cpumasks_hier() */
+};
+
+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);
+}
+
+void inc_dl_tasks_cs(struct task_struct *p)
+{
+	struct cpuset *cs = task_cs(p);
+
+	cs->nr_deadline_tasks++;
+}
+
+void dec_dl_tasks_cs(struct task_struct *p)
+{
+	struct cpuset *cs = task_cs(p);
+
+	cs->nr_deadline_tasks--;
+}
+
+/* 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 inline int is_partition_valid(const struct cpuset *cs)
+{
+	return cs->partition_root_state > 0;
+}
+
+static inline int is_partition_invalid(const struct cpuset *cs)
+{
+	return cs->partition_root_state < 0;
+}
+
+/*
+ * Callers should hold callback_lock to modify partition_root_state.
+ */
+static inline void make_partition_invalid(struct cpuset *cs)
+{
+	if (is_partition_valid(cs))
+		cs->partition_root_state = -cs->partition_root_state;
+}
+
+/*
+ * Send notification event of whenever partition_root_state changes.
+ */
+static inline void notify_partition_change(struct cpuset *cs, int old_prs)
+{
+	if (old_prs == cs->partition_root_state)
+		return;
+	cgroup_file_notify(&cs->partition_file);
+
+	/* Reset prs_err if not invalid */
+	if (is_partition_valid(cs))
+		WRITE_ONCE(cs->prs_err, PERR_NONE);
+}
+
+static struct cpuset top_cpuset = {
+	.flags = ((1 << CS_ONLINE) | (1 << CS_CPU_EXCLUSIVE) |
+		  (1 << CS_MEM_EXCLUSIVE)),
+	.partition_root_state = PRS_ROOT,
+};
+
+/**
+ * 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.  The cpuset code uses only cpuset_mutex. Other kernel subsystems
+ * can use cpuset_lock()/cpuset_unlock() to prevent change to cpuset
+ * structures. Note that cpuset_mutex needs to be a mutex as it is used in
+ * paths that rely on priority inheritance (e.g. scheduler - on RT) for
+ * correctness.
+ *
+ * A task must hold both locks to modify cpusets.  If a task holds
+ * cpuset_mutex, it blocks others, 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);
+
+void cpuset_lock(void)
+{
+	mutex_lock(&cpuset_mutex);
+}
+
+void cpuset_unlock(void)
+{
+	mutex_unlock(&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);
+
+static inline void check_insane_mems_config(nodemask_t *nodes)
+{
+	if (!cpusets_insane_config() &&
+		movable_only_nodes(nodes)) {
+		static_branch_enable(&cpusets_insane_config_key);
+		pr_info("Unsupported (movable nodes only) cpuset configuration detected (nmask=%*pbl)!\n"
+			"Cpuset allocations might fail even with a lot of memory available.\n",
+			nodemask_pr_args(nodes));
+	}
+}
+
+/*
+ * Cgroup v2 behavior is used on the "cpus" and "mems" control files when
+ * on default hierarchy or when the cpuset_v2_mode flag is set by mounting
+ * the v1 cpuset cgroup filesystem with the "cpuset_v2_mode" mount option.
+ * With v2 behavior, "cpus" and "mems" are always what the users have
+ * requested and won't be changed by hotplug events. Only the effective
+ * cpus or mems will be affected.
+ */
+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);
+}
+
+/**
+ * partition_is_populated - check if partition has tasks
+ * @cs: partition root to be checked
+ * @excluded_child: a child cpuset to be excluded in task checking
+ * Return: true if there are tasks, false otherwise
+ *
+ * It is assumed that @cs is a valid partition root. @excluded_child should
+ * be non-NULL when this cpuset is going to become a partition itself.
+ */
+static inline bool partition_is_populated(struct cpuset *cs,
+					  struct cpuset *excluded_child)
+{
+	struct cgroup_subsys_state *css;
+	struct cpuset *child;
+
+	if (cs->css.cgroup->nr_populated_csets)
+		return true;
+	if (!excluded_child && !cs->nr_subparts_cpus)
+		return cgroup_is_populated(cs->css.cgroup);
+
+	rcu_read_lock();
+	cpuset_for_each_child(child, css, cs) {
+		if (child == excluded_child)
+			continue;
+		if (is_partition_valid(child))
+			continue;
+		if (cgroup_is_populated(child->css.cgroup)) {
+			rcu_read_unlock();
+			return true;
+		}
+	}
+	rcu_read_unlock();
+	return false;
+}
+
+/*
+ * Return in pmask the portion of a task's cpusets's cpus_allowed that
+ * are online and are capable of running the task.  If none are found,
+ * walk up the cpuset hierarchy until we find one that does have some
+ * appropriate 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 task_struct *tsk,
+				  struct cpumask *pmask)
+{
+	const struct cpumask *possible_mask = task_cpu_possible_mask(tsk);
+	struct cpuset *cs;
+
+	if (WARN_ON(!cpumask_and(pmask, possible_mask, cpu_online_mask)))
+		cpumask_copy(pmask, cpu_online_mask);
+
+	rcu_read_lock();
+	cs = task_cs(tsk);
+
+	while (!cpumask_intersects(cs->effective_cpus, pmask)) {
+		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 be
+			 * identical to cpu_online_mask.
+			 */
+			goto out_unlock;
+		}
+	}
+	cpumask_and(pmask, pmask, cs->effective_cpus);
+
+out_unlock:
+	rcu_read_unlock();
+}
+
+/*
+ * 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. The check can be skipped
+ * if on default hierarchy.
+ */
+static void cpuset_update_task_spread_flags(struct cpuset *cs,
+					struct task_struct *tsk)
+{
+	if (cgroup_subsys_on_dfl(cpuset_cgrp_subsys))
+		return;
+
+	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_cpumasks - allocate three cpumasks for cpuset
+ * @cs:  the cpuset that have cpumasks to be allocated.
+ * @tmp: the tmpmasks structure pointer
+ * Return: 0 if successful, -ENOMEM otherwise.
+ *
+ * Only one of the two input arguments should be non-NULL.
+ */
+static inline int alloc_cpumasks(struct cpuset *cs, struct tmpmasks *tmp)
+{
+	cpumask_var_t *pmask1, *pmask2, *pmask3;
+
+	if (cs) {
+		pmask1 = &cs->cpus_allowed;
+		pmask2 = &cs->effective_cpus;
+		pmask3 = &cs->subparts_cpus;
+	} else {
+		pmask1 = &tmp->new_cpus;
+		pmask2 = &tmp->addmask;
+		pmask3 = &tmp->delmask;
+	}
+
+	if (!zalloc_cpumask_var(pmask1, GFP_KERNEL))
+		return -ENOMEM;
+
+	if (!zalloc_cpumask_var(pmask2, GFP_KERNEL))
+		goto free_one;
+
+	if (!zalloc_cpumask_var(pmask3, GFP_KERNEL))
+		goto free_two;
+
+	return 0;
+
+free_two:
+	free_cpumask_var(*pmask2);
+free_one:
+	free_cpumask_var(*pmask1);
+	return -ENOMEM;
+}
+
+/**
+ * free_cpumasks - free cpumasks in a tmpmasks structure
+ * @cs:  the cpuset that have cpumasks to be free.
+ * @tmp: the tmpmasks structure pointer
+ */
+static inline void free_cpumasks(struct cpuset *cs, struct tmpmasks *tmp)
+{
+	if (cs) {
+		free_cpumask_var(cs->cpus_allowed);
+		free_cpumask_var(cs->effective_cpus);
+		free_cpumask_var(cs->subparts_cpus);
+	}
+	if (tmp) {
+		free_cpumask_var(tmp->new_cpus);
+		free_cpumask_var(tmp->addmask);
+		free_cpumask_var(tmp->delmask);
+	}
+}
+
+/**
+ * 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_cpumasks(trial, NULL)) {
+		kfree(trial);
+		return NULL;
+	}
+
+	cpumask_copy(trial->cpus_allowed, cs->cpus_allowed);
+	cpumask_copy(trial->effective_cpus, cs->effective_cpus);
+	return trial;
+}
+
+/**
+ * free_cpuset - free the cpuset
+ * @cs: the cpuset to be freed
+ */
+static inline void free_cpuset(struct cpuset *cs)
+{
+	free_cpumasks(cs, NULL);
+	kfree(cs);
+}
+
+/*
+ * validate_change_legacy() - Validate conditions specific to legacy (v1)
+ *                            behavior.
+ */
+static int validate_change_legacy(struct cpuset *cur, struct cpuset *trial)
+{
+	struct cgroup_subsys_state *css;
+	struct cpuset *c, *par;
+	int ret;
+
+	WARN_ON_ONCE(!rcu_read_lock_held());
+
+	/* 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;
+
+	/* On legacy hierarchy, we must be a subset of our parent cpuset. */
+	ret = -EACCES;
+	par = parent_cs(cur);
+	if (par && !is_cpuset_subset(trial, par))
+		goto out;
+
+	ret = 0;
+out:
+	return ret;
+}
+
+/*
+ * 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 = 0;
+
+	rcu_read_lock();
+
+	if (!is_in_v2_mode())
+		ret = validate_change_legacy(cur, trial);
+	if (ret)
+		goto out;
+
+	/* Remaining checks don't apply to root cpuset */
+	if (cur == &top_cpuset)
+		goto out;
+
+	par = parent_cs(cur);
+
+	/*
+	 * 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;
+
+	/*
+	 * 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;
+	}
+
+	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/admin-guide/cgroup-v1/cpusets.rst
+ * 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:
+ *    cp - cpuset pointer, used (together with pos_css) to perform a
+ *	   top-down scan of all cpusets. 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;	/* top-down scan of cpusets */
+	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;
+	bool root_load_balance = is_sched_load_balance(&top_cpuset);
+
+	doms = NULL;
+	dattr = NULL;
+	csa = NULL;
+
+	/* Special case for the 99% of systems with one, full, sched domain */
+	if (root_load_balance && !top_cpuset.nr_subparts_cpus) {
+		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_TYPE_DOMAIN));
+
+		goto done;
+	}
+
+	csa = kmalloc_array(nr_cpusets(), sizeof(cp), GFP_KERNEL);
+	if (!csa)
+		goto done;
+	csn = 0;
+
+	rcu_read_lock();
+	if (root_load_balance)
+		csa[csn++] = &top_cpuset;
+	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 root is load-balancing, we can skip @cp if it
+		 * is a subset of the root's effective_cpus.
+		 */
+		if (!cpumask_empty(cp->cpus_allowed) &&
+		    !(is_sched_load_balance(cp) &&
+		      cpumask_intersects(cp->cpus_allowed,
+					 housekeeping_cpumask(HK_TYPE_DOMAIN))))
+			continue;
+
+		if (root_load_balance &&
+		    cpumask_subset(cp->cpus_allowed, top_cpuset.effective_cpus))
+			continue;
+
+		if (is_sched_load_balance(cp) &&
+		    !cpumask_empty(cp->effective_cpus))
+			csa[csn++] = cp;
+
+		/* skip @cp's subtree if not a partition root */
+		if (!is_partition_valid(cp))
+			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_TYPE_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;
+}
+
+static void dl_update_tasks_root_domain(struct cpuset *cs)
+{
+	struct css_task_iter it;
+	struct task_struct *task;
+
+	if (cs->nr_deadline_tasks == 0)
+		return;
+
+	css_task_iter_start(&cs->css, 0, &it);
+
+	while ((task = css_task_iter_next(&it)))
+		dl_add_task_root_domain(task);
+
+	css_task_iter_end(&it);
+}
+
+static void dl_rebuild_rd_accounting(void)
+{
+	struct cpuset *cs = NULL;
+	struct cgroup_subsys_state *pos_css;
+
+	lockdep_assert_held(&cpuset_mutex);
+	lockdep_assert_cpus_held();
+	lockdep_assert_held(&sched_domains_mutex);
+
+	rcu_read_lock();
+
+	/*
+	 * Clear default root domain DL accounting, it will be computed again
+	 * if a task belongs to it.
+	 */
+	dl_clear_root_domain(&def_root_domain);
+
+	cpuset_for_each_descendant_pre(cs, pos_css, &top_cpuset) {
+
+		if (cpumask_empty(cs->effective_cpus)) {
+			pos_css = css_rightmost_descendant(pos_css);
+			continue;
+		}
+
+		css_get(&cs->css);
+
+		rcu_read_unlock();
+
+		dl_update_tasks_root_domain(cs);
+
+		rcu_read_lock();
+		css_put(&cs->css);
+	}
+	rcu_read_unlock();
+}
+
+static void
+partition_and_rebuild_sched_domains(int ndoms_new, cpumask_var_t doms_new[],
+				    struct sched_domain_attr *dattr_new)
+{
+	mutex_lock(&sched_domains_mutex);
+	partition_sched_domains_locked(ndoms_new, doms_new, dattr_new);
+	dl_rebuild_rd_accounting();
+	mutex_unlock(&sched_domains_mutex);
+}
+
+/*
+ * 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 cpus_read_lock().
+ */
+static void rebuild_sched_domains_locked(void)
+{
+	struct cgroup_subsys_state *pos_css;
+	struct sched_domain_attr *attr;
+	cpumask_var_t *doms;
+	struct cpuset *cs;
+	int ndoms;
+
+	lockdep_assert_cpus_held();
+	lockdep_assert_held(&cpuset_mutex);
+
+	/*
+	 * If we have raced with CPU hotplug, return early to avoid
+	 * passing doms with offlined cpu to partition_sched_domains().
+	 * Anyways, cpuset_hotplug_workfn() will rebuild sched domains.
+	 *
+	 * With no CPUs in any subpartitions, top_cpuset's effective CPUs
+	 * should be the same as the active CPUs, so checking only top_cpuset
+	 * is enough to detect racing CPU offlines.
+	 */
+	if (!top_cpuset.nr_subparts_cpus &&
+	    !cpumask_equal(top_cpuset.effective_cpus, cpu_active_mask))
+		return;
+
+	/*
+	 * With subpartition CPUs, however, the effective CPUs of a partition
+	 * root should be only a subset of the active CPUs.  Since a CPU in any
+	 * partition root could be offlined, all must be checked.
+	 */
+	if (top_cpuset.nr_subparts_cpus) {
+		rcu_read_lock();
+		cpuset_for_each_descendant_pre(cs, pos_css, &top_cpuset) {
+			if (!is_partition_valid(cs)) {
+				pos_css = css_rightmost_descendant(pos_css);
+				continue;
+			}
+			if (!cpumask_subset(cs->effective_cpus,
+					    cpu_active_mask)) {
+				rcu_read_unlock();
+				return;
+			}
+		}
+		rcu_read_unlock();
+	}
+
+	/* Generate domain masks and attrs */
+	ndoms = generate_sched_domains(&doms, &attr);
+
+	/* Have scheduler rebuild the domains */
+	partition_and_rebuild_sched_domains(ndoms, doms, attr);
+}
+#else /* !CONFIG_SMP */
+static void rebuild_sched_domains_locked(void)
+{
+}
+#endif /* CONFIG_SMP */
+
+void rebuild_sched_domains(void)
+{
+	cpus_read_lock();
+	mutex_lock(&cpuset_mutex);
+	rebuild_sched_domains_locked();
+	mutex_unlock(&cpuset_mutex);
+	cpus_read_unlock();
+}
+
+/**
+ * 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
+ * @new_cpus: the temp variable for the new effective_cpus mask
+ *
+ * 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. For top_cpuset, task_cpu_possible_mask()
+ * is used instead of effective_cpus to make sure all offline CPUs are also
+ * included as hotplug code won't update cpumasks for tasks in top_cpuset.
+ */
+static void update_tasks_cpumask(struct cpuset *cs, struct cpumask *new_cpus)
+{
+	struct css_task_iter it;
+	struct task_struct *task;
+	bool top_cs = cs == &top_cpuset;
+
+	css_task_iter_start(&cs->css, 0, &it);
+	while ((task = css_task_iter_next(&it))) {
+		const struct cpumask *possible_mask = task_cpu_possible_mask(task);
+
+		if (top_cs) {
+			/*
+			 * Percpu kthreads in top_cpuset are ignored
+			 */
+			if (kthread_is_per_cpu(task))
+				continue;
+			cpumask_andnot(new_cpus, possible_mask, cs->subparts_cpus);
+		} else {
+			cpumask_and(new_cpus, possible_mask, cs->effective_cpus);
+		}
+		set_cpus_allowed_ptr(task, new_cpus);
+	}
+	css_task_iter_end(&it);
+}
+
+/**
+ * compute_effective_cpumask - Compute the effective cpumask of the cpuset
+ * @new_cpus: the temp variable for the new effective_cpus mask
+ * @cs: the cpuset the need to recompute the new effective_cpus mask
+ * @parent: the parent cpuset
+ *
+ * If the parent has subpartition CPUs, include them in the list of
+ * allowable CPUs in computing the new effective_cpus mask. Since offlined
+ * CPUs are not removed from subparts_cpus, we have to use cpu_active_mask
+ * to mask those out.
+ */
+static void compute_effective_cpumask(struct cpumask *new_cpus,
+				      struct cpuset *cs, struct cpuset *parent)
+{
+	if (parent->nr_subparts_cpus && is_partition_valid(cs)) {
+		cpumask_or(new_cpus, parent->effective_cpus,
+			   parent->subparts_cpus);
+		cpumask_and(new_cpus, new_cpus, cs->cpus_allowed);
+		cpumask_and(new_cpus, new_cpus, cpu_active_mask);
+	} else {
+		cpumask_and(new_cpus, cs->cpus_allowed, parent->effective_cpus);
+	}
+}
+
+/*
+ * Commands for update_parent_subparts_cpumask
+ */
+enum subparts_cmd {
+	partcmd_enable,		/* Enable partition root	 */
+	partcmd_disable,	/* Disable partition root	 */
+	partcmd_update,		/* Update parent's subparts_cpus */
+	partcmd_invalidate,	/* Make partition invalid	 */
+};
+
+static int update_flag(cpuset_flagbits_t bit, struct cpuset *cs,
+		       int turning_on);
+static void update_sibling_cpumasks(struct cpuset *parent, struct cpuset *cs,
+				    struct tmpmasks *tmp);
+
+/*
+ * Update partition exclusive flag
+ *
+ * Return: 0 if successful, an error code otherwise
+ */
+static int update_partition_exclusive(struct cpuset *cs, int new_prs)
+{
+	bool exclusive = (new_prs > 0);
+
+	if (exclusive && !is_cpu_exclusive(cs)) {
+		if (update_flag(CS_CPU_EXCLUSIVE, cs, 1))
+			return PERR_NOTEXCL;
+	} else if (!exclusive && is_cpu_exclusive(cs)) {
+		/* Turning off CS_CPU_EXCLUSIVE will not return error */
+		update_flag(CS_CPU_EXCLUSIVE, cs, 0);
+	}
+	return 0;
+}
+
+/*
+ * Update partition load balance flag and/or rebuild sched domain
+ *
+ * Changing load balance flag will automatically call
+ * rebuild_sched_domains_locked().
+ * This function is for cgroup v2 only.
+ */
+static void update_partition_sd_lb(struct cpuset *cs, int old_prs)
+{
+	int new_prs = cs->partition_root_state;
+	bool rebuild_domains = (new_prs > 0) || (old_prs > 0);
+	bool new_lb;
+
+	/*
+	 * If cs is not a valid partition root, the load balance state
+	 * will follow its parent.
+	 */
+	if (new_prs > 0) {
+		new_lb = (new_prs != PRS_ISOLATED);
+	} else {
+		new_lb = is_sched_load_balance(parent_cs(cs));
+	}
+	if (new_lb != !!is_sched_load_balance(cs)) {
+		rebuild_domains = true;
+		if (new_lb)
+			set_bit(CS_SCHED_LOAD_BALANCE, &cs->flags);
+		else
+			clear_bit(CS_SCHED_LOAD_BALANCE, &cs->flags);
+	}
+
+	if (rebuild_domains)
+		rebuild_sched_domains_locked();
+}
+
+/**
+ * update_parent_subparts_cpumask - update subparts_cpus mask of parent cpuset
+ * @cs:      The cpuset that requests change in partition root state
+ * @cmd:     Partition root state change command
+ * @newmask: Optional new cpumask for partcmd_update
+ * @tmp:     Temporary addmask and delmask
+ * Return:   0 or a partition root state error code
+ *
+ * For partcmd_enable, the cpuset is being transformed from a non-partition
+ * root to a partition root. The cpus_allowed mask of the given cpuset will
+ * be put into parent's subparts_cpus and taken away from parent's
+ * effective_cpus. The function will return 0 if all the CPUs listed in
+ * cpus_allowed can be granted or an error code will be returned.
+ *
+ * For partcmd_disable, the cpuset is being transformed from a partition
+ * root back to a non-partition root. Any CPUs in cpus_allowed that are in
+ * parent's subparts_cpus will be taken away from that cpumask and put back
+ * into parent's effective_cpus. 0 will always be returned.
+ *
+ * For partcmd_update, if the optional newmask is specified, the cpu list is
+ * to be changed from cpus_allowed to newmask. Otherwise, cpus_allowed is
+ * assumed to remain the same. The cpuset should either be a valid or invalid
+ * partition root. The partition root state may change from valid to invalid
+ * or vice versa. An error code will only be returned if transitioning from
+ * invalid to valid violates the exclusivity rule.
+ *
+ * For partcmd_invalidate, the current partition will be made invalid.
+ *
+ * The partcmd_enable and partcmd_disable commands are used by
+ * update_prstate(). An error code may be returned and the caller will check
+ * for error.
+ *
+ * The partcmd_update command is used by update_cpumasks_hier() with newmask
+ * NULL and update_cpumask() with newmask set. The partcmd_invalidate is used
+ * by update_cpumask() with NULL newmask. In both cases, the callers won't
+ * check for error and so partition_root_state and prs_error will be updated
+ * directly.
+ */
+static int update_parent_subparts_cpumask(struct cpuset *cs, int cmd,
+					  struct cpumask *newmask,
+					  struct tmpmasks *tmp)
+{
+	struct cpuset *parent = parent_cs(cs);
+	int adding;	/* Moving cpus from effective_cpus to subparts_cpus */
+	int deleting;	/* Moving cpus from subparts_cpus to effective_cpus */
+	int old_prs, new_prs;
+	int part_error = PERR_NONE;	/* Partition error? */
+
+	lockdep_assert_held(&cpuset_mutex);
+
+	/*
+	 * The parent must be a partition root.
+	 * The new cpumask, if present, or the current cpus_allowed must
+	 * not be empty.
+	 */
+	if (!is_partition_valid(parent)) {
+		return is_partition_invalid(parent)
+		       ? PERR_INVPARENT : PERR_NOTPART;
+	}
+	if (!newmask && cpumask_empty(cs->cpus_allowed))
+		return PERR_CPUSEMPTY;
+
+	/*
+	 * new_prs will only be changed for the partcmd_update and
+	 * partcmd_invalidate commands.
+	 */
+	adding = deleting = false;
+	old_prs = new_prs = cs->partition_root_state;
+	if (cmd == partcmd_enable) {
+		/*
+		 * Enabling partition root is not allowed if cpus_allowed
+		 * doesn't overlap parent's cpus_allowed.
+		 */
+		if (!cpumask_intersects(cs->cpus_allowed, parent->cpus_allowed))
+			return PERR_INVCPUS;
+
+		/*
+		 * A parent can be left with no CPU as long as there is no
+		 * task directly associated with the parent partition.
+		 */
+		if (cpumask_subset(parent->effective_cpus, cs->cpus_allowed) &&
+		    partition_is_populated(parent, cs))
+			return PERR_NOCPUS;
+
+		cpumask_copy(tmp->addmask, cs->cpus_allowed);
+		adding = true;
+	} else if (cmd == partcmd_disable) {
+		/*
+		 * Need to remove cpus from parent's subparts_cpus for valid
+		 * partition root.
+		 */
+		deleting = !is_prs_invalid(old_prs) &&
+			   cpumask_and(tmp->delmask, cs->cpus_allowed,
+				       parent->subparts_cpus);
+	} else if (cmd == partcmd_invalidate) {
+		if (is_prs_invalid(old_prs))
+			return 0;
+
+		/*
+		 * Make the current partition invalid. It is assumed that
+		 * invalidation is caused by violating cpu exclusivity rule.
+		 */
+		deleting = cpumask_and(tmp->delmask, cs->cpus_allowed,
+				       parent->subparts_cpus);
+		if (old_prs > 0) {
+			new_prs = -old_prs;
+			part_error = PERR_NOTEXCL;
+		}
+	} else if (newmask) {
+		/*
+		 * partcmd_update with newmask:
+		 *
+		 * Compute add/delete mask to/from subparts_cpus
+		 *
+		 * delmask = cpus_allowed & ~newmask & parent->subparts_cpus
+		 * addmask = newmask & parent->cpus_allowed
+		 *		     & ~parent->subparts_cpus
+		 */
+		cpumask_andnot(tmp->delmask, cs->cpus_allowed, newmask);
+		deleting = cpumask_and(tmp->delmask, tmp->delmask,
+				       parent->subparts_cpus);
+
+		cpumask_and(tmp->addmask, newmask, parent->cpus_allowed);
+		adding = cpumask_andnot(tmp->addmask, tmp->addmask,
+					parent->subparts_cpus);
+		/*
+		 * Empty cpumask is not allowed
+		 */
+		if (cpumask_empty(newmask)) {
+			part_error = PERR_CPUSEMPTY;
+		/*
+		 * Make partition invalid if parent's effective_cpus could
+		 * become empty and there are tasks in the parent.
+		 */
+		} else if (adding &&
+		    cpumask_subset(parent->effective_cpus, tmp->addmask) &&
+		    !cpumask_intersects(tmp->delmask, cpu_active_mask) &&
+		    partition_is_populated(parent, cs)) {
+			part_error = PERR_NOCPUS;
+			adding = false;
+			deleting = cpumask_and(tmp->delmask, cs->cpus_allowed,
+					       parent->subparts_cpus);
+		}
+	} else {
+		/*
+		 * partcmd_update w/o newmask:
+		 *
+		 * delmask = cpus_allowed & parent->subparts_cpus
+		 * addmask = cpus_allowed & parent->cpus_allowed
+		 *			  & ~parent->subparts_cpus
+		 *
+		 * This gets invoked either due to a hotplug event or from
+		 * update_cpumasks_hier(). This can cause the state of a
+		 * partition root to transition from valid to invalid or vice
+		 * versa. So we still need to compute the addmask and delmask.
+
+		 * A partition error happens when:
+		 * 1) Cpuset is valid partition, but parent does not distribute
+		 *    out any CPUs.
+		 * 2) Parent has tasks and all its effective CPUs will have
+		 *    to be distributed out.
+		 */
+		cpumask_and(tmp->addmask, cs->cpus_allowed,
+					  parent->cpus_allowed);
+		adding = cpumask_andnot(tmp->addmask, tmp->addmask,
+					parent->subparts_cpus);
+
+		if ((is_partition_valid(cs) && !parent->nr_subparts_cpus) ||
+		    (adding &&
+		     cpumask_subset(parent->effective_cpus, tmp->addmask) &&
+		     partition_is_populated(parent, cs))) {
+			part_error = PERR_NOCPUS;
+			adding = false;
+		}
+
+		if (part_error && is_partition_valid(cs) &&
+		    parent->nr_subparts_cpus)
+			deleting = cpumask_and(tmp->delmask, cs->cpus_allowed,
+					       parent->subparts_cpus);
+	}
+	if (part_error)
+		WRITE_ONCE(cs->prs_err, part_error);
+
+	if (cmd == partcmd_update) {
+		/*
+		 * Check for possible transition between valid and invalid
+		 * partition root.
+		 */
+		switch (cs->partition_root_state) {
+		case PRS_ROOT:
+		case PRS_ISOLATED:
+			if (part_error)
+				new_prs = -old_prs;
+			break;
+		case PRS_INVALID_ROOT:
+		case PRS_INVALID_ISOLATED:
+			if (!part_error)
+				new_prs = -old_prs;
+			break;
+		}
+	}
+
+	if (!adding && !deleting && (new_prs == old_prs))
+		return 0;
+
+	/*
+	 * Transitioning between invalid to valid or vice versa may require
+	 * changing CS_CPU_EXCLUSIVE.
+	 */
+	if (old_prs != new_prs) {
+		int err = update_partition_exclusive(cs, new_prs);
+
+		if (err)
+			return err;
+	}
+
+	/*
+	 * Change the parent's subparts_cpus.
+	 * Newly added CPUs will be removed from effective_cpus and
+	 * newly deleted ones will be added back to effective_cpus.
+	 */
+	spin_lock_irq(&callback_lock);
+	if (adding) {
+		cpumask_or(parent->subparts_cpus,
+			   parent->subparts_cpus, tmp->addmask);
+		cpumask_andnot(parent->effective_cpus,
+			       parent->effective_cpus, tmp->addmask);
+	}
+	if (deleting) {
+		cpumask_andnot(parent->subparts_cpus,
+			       parent->subparts_cpus, tmp->delmask);
+		/*
+		 * Some of the CPUs in subparts_cpus might have been offlined.
+		 */
+		cpumask_and(tmp->delmask, tmp->delmask, cpu_active_mask);
+		cpumask_or(parent->effective_cpus,
+			   parent->effective_cpus, tmp->delmask);
+	}
+
+	parent->nr_subparts_cpus = cpumask_weight(parent->subparts_cpus);
+
+	if (old_prs != new_prs)
+		cs->partition_root_state = new_prs;
+
+	spin_unlock_irq(&callback_lock);
+
+	if (adding || deleting) {
+		update_tasks_cpumask(parent, tmp->addmask);
+		if (parent->child_ecpus_count)
+			update_sibling_cpumasks(parent, cs, tmp);
+	}
+
+	/*
+	 * For partcmd_update without newmask, it is being called from
+	 * cpuset_hotplug_workfn() where cpus_read_lock() wasn't taken.
+	 * Update the load balance flag and scheduling domain if
+	 * cpus_read_trylock() is successful.
+	 */
+	if ((cmd == partcmd_update) && !newmask && cpus_read_trylock()) {
+		update_partition_sd_lb(cs, old_prs);
+		cpus_read_unlock();
+	}
+
+	notify_partition_change(cs, old_prs);
+	return 0;
+}
+
+/*
+ * update_cpumasks_hier() flags
+ */
+#define HIER_CHECKALL		0x01	/* Check all cpusets with no skipping */
+#define HIER_NO_SD_REBUILD	0x02	/* Don't rebuild sched domains */
+
+/*
+ * update_cpumasks_hier - Update effective cpumasks and tasks in the subtree
+ * @cs:  the cpuset to consider
+ * @tmp: temp variables for calculating effective_cpus & partition setup
+ * @force: don't skip any descendant cpusets if set
+ *
+ * When configured cpumask is changed, the effective cpumasks of this cpuset
+ * and all its descendants need to be updated.
+ *
+ * On legacy hierarchy, effective_cpus will be the same with cpu_allowed.
+ *
+ * Called with cpuset_mutex held
+ */
+static void update_cpumasks_hier(struct cpuset *cs, struct tmpmasks *tmp,
+				 int flags)
+{
+	struct cpuset *cp;
+	struct cgroup_subsys_state *pos_css;
+	bool need_rebuild_sched_domains = false;
+	int old_prs, new_prs;
+
+	rcu_read_lock();
+	cpuset_for_each_descendant_pre(cp, pos_css, cs) {
+		struct cpuset *parent = parent_cs(cp);
+		bool update_parent = false;
+
+		compute_effective_cpumask(tmp->new_cpus, cp, parent);
+
+		/*
+		 * If it becomes empty, inherit the effective mask of the
+		 * parent, which is guaranteed to have some CPUs unless
+		 * it is a partition root that has explicitly distributed
+		 * out all its CPUs.
+		 */
+		if (is_in_v2_mode() && cpumask_empty(tmp->new_cpus)) {
+			if (is_partition_valid(cp) &&
+			    cpumask_equal(cp->cpus_allowed, cp->subparts_cpus))
+				goto update_parent_subparts;
+
+			cpumask_copy(tmp->new_cpus, parent->effective_cpus);
+			if (!cp->use_parent_ecpus) {
+				cp->use_parent_ecpus = true;
+				parent->child_ecpus_count++;
+			}
+		} else if (cp->use_parent_ecpus) {
+			cp->use_parent_ecpus = false;
+			WARN_ON_ONCE(!parent->child_ecpus_count);
+			parent->child_ecpus_count--;
+		}
+
+		/*
+		 * Skip the whole subtree if
+		 * 1) the cpumask remains the same,
+		 * 2) has no partition root state,
+		 * 3) HIER_CHECKALL flag not set, and
+		 * 4) for v2 load balance state same as its parent.
+		 */
+		if (!cp->partition_root_state && !(flags & HIER_CHECKALL) &&
+		    cpumask_equal(tmp->new_cpus, cp->effective_cpus) &&
+		    (!cgroup_subsys_on_dfl(cpuset_cgrp_subsys) ||
+		    (is_sched_load_balance(parent) == is_sched_load_balance(cp)))) {
+			pos_css = css_rightmost_descendant(pos_css);
+			continue;
+		}
+
+update_parent_subparts:
+		/*
+		 * update_parent_subparts_cpumask() should have been called
+		 * for cs already in update_cpumask(). We should also call
+		 * update_tasks_cpumask() again for tasks in the parent
+		 * cpuset if the parent's subparts_cpus changes.
+		 */
+		old_prs = new_prs = cp->partition_root_state;
+		if ((cp != cs) && old_prs) {
+			switch (parent->partition_root_state) {
+			case PRS_ROOT:
+			case PRS_ISOLATED:
+				update_parent = true;
+				break;
+
+			default:
+				/*
+				 * When parent is not a partition root or is
+				 * invalid, child partition roots become
+				 * invalid too.
+				 */
+				if (is_partition_valid(cp))
+					new_prs = -cp->partition_root_state;
+				WRITE_ONCE(cp->prs_err,
+					   is_partition_invalid(parent)
+					   ? PERR_INVPARENT : PERR_NOTPART);
+				break;
+			}
+		}
+
+		if (!css_tryget_online(&cp->css))
+			continue;
+		rcu_read_unlock();
+
+		if (update_parent) {
+			update_parent_subparts_cpumask(cp, partcmd_update, NULL,
+						       tmp);
+			/*
+			 * The cpuset partition_root_state may become
+			 * invalid. Capture it.
+			 */
+			new_prs = cp->partition_root_state;
+		}
+
+		spin_lock_irq(&callback_lock);
+
+		if (cp->nr_subparts_cpus && !is_partition_valid(cp)) {
+			/*
+			 * Put all active subparts_cpus back to effective_cpus.
+			 */
+			cpumask_or(tmp->new_cpus, tmp->new_cpus,
+				   cp->subparts_cpus);
+			cpumask_and(tmp->new_cpus, tmp->new_cpus,
+				   cpu_active_mask);
+			cp->nr_subparts_cpus = 0;
+			cpumask_clear(cp->subparts_cpus);
+		}
+
+		cpumask_copy(cp->effective_cpus, tmp->new_cpus);
+		if (cp->nr_subparts_cpus) {
+			/*
+			 * Make sure that effective_cpus & subparts_cpus
+			 * are mutually exclusive.
+			 */
+			cpumask_andnot(cp->effective_cpus, cp->effective_cpus,
+				       cp->subparts_cpus);
+		}
+
+		cp->partition_root_state = new_prs;
+		spin_unlock_irq(&callback_lock);
+
+		notify_partition_change(cp, old_prs);
+
+		WARN_ON(!is_in_v2_mode() &&
+			!cpumask_equal(cp->cpus_allowed, cp->effective_cpus));
+
+		update_tasks_cpumask(cp, tmp->new_cpus);
+
+		/*
+		 * On default hierarchy, inherit the CS_SCHED_LOAD_BALANCE
+		 * from parent if current cpuset isn't a valid partition root
+		 * and their load balance states differ.
+		 */
+		if (cgroup_subsys_on_dfl(cpuset_cgrp_subsys) &&
+		    !is_partition_valid(cp) &&
+		    (is_sched_load_balance(parent) != is_sched_load_balance(cp))) {
+			if (is_sched_load_balance(parent))
+				set_bit(CS_SCHED_LOAD_BALANCE, &cp->flags);
+			else
+				clear_bit(CS_SCHED_LOAD_BALANCE, &cp->flags);
+		}
+
+		/*
+		 * On legacy hierarchy, if the effective cpumask of any non-
+		 * empty cpuset is changed, we need to rebuild sched domains.
+		 * On default hierarchy, the cpuset needs to be a partition
+		 * root as well.
+		 */
+		if (!cpumask_empty(cp->cpus_allowed) &&
+		    is_sched_load_balance(cp) &&
+		   (!cgroup_subsys_on_dfl(cpuset_cgrp_subsys) ||
+		    is_partition_valid(cp)))
+			need_rebuild_sched_domains = true;
+
+		rcu_read_lock();
+		css_put(&cp->css);
+	}
+	rcu_read_unlock();
+
+	if (need_rebuild_sched_domains && !(flags & HIER_NO_SD_REBUILD))
+		rebuild_sched_domains_locked();
+}
+
+/**
+ * update_sibling_cpumasks - Update siblings cpumasks
+ * @parent:  Parent cpuset
+ * @cs:      Current cpuset
+ * @tmp:     Temp variables
+ */
+static void update_sibling_cpumasks(struct cpuset *parent, struct cpuset *cs,
+				    struct tmpmasks *tmp)
+{
+	struct cpuset *sibling;
+	struct cgroup_subsys_state *pos_css;
+
+	lockdep_assert_held(&cpuset_mutex);
+
+	/*
+	 * Check all its siblings and call update_cpumasks_hier()
+	 * if their use_parent_ecpus flag is set in order for them
+	 * to use the right effective_cpus value.
+	 *
+	 * The update_cpumasks_hier() function may sleep. So we have to
+	 * release the RCU read lock before calling it. HIER_NO_SD_REBUILD
+	 * flag is used to suppress rebuild of sched domains as the callers
+	 * will take care of that.
+	 */
+	rcu_read_lock();
+	cpuset_for_each_child(sibling, pos_css, parent) {
+		if (sibling == cs)
+			continue;
+		if (!sibling->use_parent_ecpus)
+			continue;
+		if (!css_tryget_online(&sibling->css))
+			continue;
+
+		rcu_read_unlock();
+		update_cpumasks_hier(sibling, tmp, HIER_NO_SD_REBUILD);
+		rcu_read_lock();
+		css_put(&sibling->css);
+	}
+	rcu_read_unlock();
+}
+
+/**
+ * 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;
+	struct tmpmasks tmp;
+	bool invalidate = false;
+	int old_prs = cs->partition_root_state;
+
+	/* 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;
+
+	if (alloc_cpumasks(NULL, &tmp))
+		return -ENOMEM;
+
+	retval = validate_change(cs, trialcs);
+
+	if ((retval == -EINVAL) && cgroup_subsys_on_dfl(cpuset_cgrp_subsys)) {
+		struct cpuset *cp, *parent;
+		struct cgroup_subsys_state *css;
+
+		/*
+		 * The -EINVAL error code indicates that partition sibling
+		 * CPU exclusivity rule has been violated. We still allow
+		 * the cpumask change to proceed while invalidating the
+		 * partition. However, any conflicting sibling partitions
+		 * have to be marked as invalid too.
+		 */
+		invalidate = true;
+		rcu_read_lock();
+		parent = parent_cs(cs);
+		cpuset_for_each_child(cp, css, parent)
+			if (is_partition_valid(cp) &&
+			    cpumask_intersects(trialcs->cpus_allowed, cp->cpus_allowed)) {
+				rcu_read_unlock();
+				update_parent_subparts_cpumask(cp, partcmd_invalidate, NULL, &tmp);
+				rcu_read_lock();
+			}
+		rcu_read_unlock();
+		retval = 0;
+	}
+	if (retval < 0)
+		goto out_free;
+
+	if (cs->partition_root_state) {
+		if (invalidate)
+			update_parent_subparts_cpumask(cs, partcmd_invalidate,
+						       NULL, &tmp);
+		else
+			update_parent_subparts_cpumask(cs, partcmd_update,
+						trialcs->cpus_allowed, &tmp);
+	}
+
+	compute_effective_cpumask(trialcs->effective_cpus, trialcs,
+				  parent_cs(cs));
+	spin_lock_irq(&callback_lock);
+	cpumask_copy(cs->cpus_allowed, trialcs->cpus_allowed);
+
+	/*
+	 * Make sure that subparts_cpus, if not empty, is a subset of
+	 * cpus_allowed. Clear subparts_cpus if partition not valid or
+	 * empty effective cpus with tasks.
+	 */
+	if (cs->nr_subparts_cpus) {
+		if (!is_partition_valid(cs) ||
+		   (cpumask_subset(trialcs->effective_cpus, cs->subparts_cpus) &&
+		    partition_is_populated(cs, NULL))) {
+			cs->nr_subparts_cpus = 0;
+			cpumask_clear(cs->subparts_cpus);
+		} else {
+			cpumask_and(cs->subparts_cpus, cs->subparts_cpus,
+				    cs->cpus_allowed);
+			cs->nr_subparts_cpus = cpumask_weight(cs->subparts_cpus);
+		}
+	}
+	spin_unlock_irq(&callback_lock);
+
+	/* effective_cpus will be updated here */
+	update_cpumasks_hier(cs, &tmp, 0);
+
+	if (cs->partition_root_state) {
+		struct cpuset *parent = parent_cs(cs);
+
+		/*
+		 * For partition root, update the cpumasks of sibling
+		 * cpusets if they use parent's effective_cpus.
+		 */
+		if (parent->child_ecpus_count)
+			update_sibling_cpumasks(parent, cs, &tmp);
+
+		/* Update CS_SCHED_LOAD_BALANCE and/or sched_domains */
+		update_partition_sd_lb(cs, old_prs);
+	}
+out_free:
+	free_cpumasks(NULL, &tmp);
+	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;
+
+	if (nodes_equal(*from, *to)) {
+		mmput(mm);
+		return;
+	}
+
+	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_lock, 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 hierarchy, 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_lock, 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;
+
+	check_insane_mems_config(&trialcs->mems_allowed);
+
+	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_flags(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_cpuset(trialcs);
+	return err;
+}
+
+/**
+ * update_prstate - update partition_root_state
+ * @cs: the cpuset to update
+ * @new_prs: new partition root state
+ * Return: 0 if successful, != 0 if error
+ *
+ * Call with cpuset_mutex held.
+ */
+static int update_prstate(struct cpuset *cs, int new_prs)
+{
+	int err = PERR_NONE, old_prs = cs->partition_root_state;
+	struct cpuset *parent = parent_cs(cs);
+	struct tmpmasks tmpmask;
+
+	if (old_prs == new_prs)
+		return 0;
+
+	/*
+	 * For a previously invalid partition root, leave it at being
+	 * invalid if new_prs is not "member".
+	 */
+	if (new_prs && is_prs_invalid(old_prs)) {
+		cs->partition_root_state = -new_prs;
+		return 0;
+	}
+
+	if (alloc_cpumasks(NULL, &tmpmask))
+		return -ENOMEM;
+
+	err = update_partition_exclusive(cs, new_prs);
+	if (err)
+		goto out;
+
+	if (!old_prs) {
+		/*
+		 * cpus_allowed cannot be empty.
+		 */
+		if (cpumask_empty(cs->cpus_allowed)) {
+			err = PERR_CPUSEMPTY;
+			goto out;
+		}
+
+		err = update_parent_subparts_cpumask(cs, partcmd_enable,
+						     NULL, &tmpmask);
+	} else if (old_prs && new_prs) {
+		/*
+		 * A change in load balance state only, no change in cpumasks.
+		 */
+		;
+	} else {
+		/*
+		 * Switching back to member is always allowed even if it
+		 * disables child partitions.
+		 */
+		update_parent_subparts_cpumask(cs, partcmd_disable, NULL,
+					       &tmpmask);
+
+		/*
+		 * If there are child partitions, they will all become invalid.
+		 */
+		if (unlikely(cs->nr_subparts_cpus)) {
+			spin_lock_irq(&callback_lock);
+			cs->nr_subparts_cpus = 0;
+			cpumask_clear(cs->subparts_cpus);
+			compute_effective_cpumask(cs->effective_cpus, cs, parent);
+			spin_unlock_irq(&callback_lock);
+		}
+	}
+out:
+	/*
+	 * Make partition invalid & disable CS_CPU_EXCLUSIVE if an error
+	 * happens.
+	 */
+	if (err) {
+		new_prs = -new_prs;
+		update_partition_exclusive(cs, new_prs);
+	}
+
+	spin_lock_irq(&callback_lock);
+	cs->partition_root_state = new_prs;
+	WRITE_ONCE(cs->prs_err, err);
+	spin_unlock_irq(&callback_lock);
+
+	/*
+	 * Update child cpusets, if present.
+	 * Force update if switching back to member.
+	 */
+	if (!list_empty(&cs->css.children))
+		update_cpumasks_hier(cs, &tmpmask, !new_prs ? HIER_CHECKALL : 0);
+
+	/* Update sched domains and load balance flag */
+	update_partition_sd_lb(cs, old_prs);
+
+	notify_partition_change(cs, old_prs);
+	free_cpumasks(NULL, &tmpmask);
+	return 0;
+}
+
+/*
+ * 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;
+
+/*
+ * Check to see if a cpuset can accept a new task
+ * For v1, cpus_allowed and mems_allowed can't be empty.
+ * For v2, effective_cpus can't be empty.
+ * Note that in v1, effective_cpus = cpus_allowed.
+ */
+static int cpuset_can_attach_check(struct cpuset *cs)
+{
+	if (cpumask_empty(cs->effective_cpus) ||
+	   (!is_in_v2_mode() && nodes_empty(cs->mems_allowed)))
+		return -ENOSPC;
+	return 0;
+}
+
+static void reset_migrate_dl_data(struct cpuset *cs)
+{
+	cs->nr_migrate_dl_tasks = 0;
+	cs->sum_migrate_dl_bw = 0;
+}
+
+/* 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, *oldcs;
+	struct task_struct *task;
+	bool cpus_updated, mems_updated;
+	int ret;
+
+	/* used later by cpuset_attach() */
+	cpuset_attach_old_cs = task_cs(cgroup_taskset_first(tset, &css));
+	oldcs = cpuset_attach_old_cs;
+	cs = css_cs(css);
+
+	mutex_lock(&cpuset_mutex);
+
+	/* Check to see if task is allowed in the cpuset */
+	ret = cpuset_can_attach_check(cs);
+	if (ret)
+		goto out_unlock;
+
+	cpus_updated = !cpumask_equal(cs->effective_cpus, oldcs->effective_cpus);
+	mems_updated = !nodes_equal(cs->effective_mems, oldcs->effective_mems);
+
+	cgroup_taskset_for_each(task, css, tset) {
+		ret = task_can_attach(task);
+		if (ret)
+			goto out_unlock;
+
+		/*
+		 * Skip rights over task check in v2 when nothing changes,
+		 * migration permission derives from hierarchy ownership in
+		 * cgroup_procs_write_permission()).
+		 */
+		if (!cgroup_subsys_on_dfl(cpuset_cgrp_subsys) ||
+		    (cpus_updated || mems_updated)) {
+			ret = security_task_setscheduler(task);
+			if (ret)
+				goto out_unlock;
+		}
+
+		if (dl_task(task)) {
+			cs->nr_migrate_dl_tasks++;
+			cs->sum_migrate_dl_bw += task->dl.dl_bw;
+		}
+	}
+
+	if (!cs->nr_migrate_dl_tasks)
+		goto out_success;
+
+	if (!cpumask_intersects(oldcs->effective_cpus, cs->effective_cpus)) {
+		int cpu = cpumask_any_and(cpu_active_mask, cs->effective_cpus);
+
+		if (unlikely(cpu >= nr_cpu_ids)) {
+			reset_migrate_dl_data(cs);
+			ret = -EINVAL;
+			goto out_unlock;
+		}
+
+		ret = dl_bw_alloc(cpu, cs->sum_migrate_dl_bw);
+		if (ret) {
+			reset_migrate_dl_data(cs);
+			goto out_unlock;
+		}
+	}
+
+out_success:
+	/*
+	 * Mark attach is in progress.  This makes validate_change() fail
+	 * changes which zero cpus/mems_allowed.
+	 */
+	cs->attach_in_progress++;
+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);
+	cs->attach_in_progress--;
+	if (!cs->attach_in_progress)
+		wake_up(&cpuset_attach_wq);
+
+	if (cs->nr_migrate_dl_tasks) {
+		int cpu = cpumask_any(cs->effective_cpus);
+
+		dl_bw_free(cpu, cs->sum_migrate_dl_bw);
+		reset_migrate_dl_data(cs);
+	}
+
+	mutex_unlock(&cpuset_mutex);
+}
+
+/*
+ * Protected by cpuset_mutex. cpus_attach is used only by cpuset_attach_task()
+ * but we can't allocate it dynamically there.  Define it global and
+ * allocate from cpuset_init().
+ */
+static cpumask_var_t cpus_attach;
+static nodemask_t cpuset_attach_nodemask_to;
+
+static void cpuset_attach_task(struct cpuset *cs, struct task_struct *task)
+{
+	lockdep_assert_held(&cpuset_mutex);
+
+	if (cs != &top_cpuset)
+		guarantee_online_cpus(task, cpus_attach);
+	else
+		cpumask_andnot(cpus_attach, task_cpu_possible_mask(task),
+			       cs->subparts_cpus);
+	/*
+	 * 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_flags(cs, task);
+}
+
+static void cpuset_attach(struct cgroup_taskset *tset)
+{
+	struct task_struct *task;
+	struct task_struct *leader;
+	struct cgroup_subsys_state *css;
+	struct cpuset *cs;
+	struct cpuset *oldcs = cpuset_attach_old_cs;
+	bool cpus_updated, mems_updated;
+
+	cgroup_taskset_first(tset, &css);
+	cs = css_cs(css);
+
+	lockdep_assert_cpus_held();	/* see cgroup_attach_lock() */
+	mutex_lock(&cpuset_mutex);
+	cpus_updated = !cpumask_equal(cs->effective_cpus,
+				      oldcs->effective_cpus);
+	mems_updated = !nodes_equal(cs->effective_mems, oldcs->effective_mems);
+
+	/*
+	 * In the default hierarchy, enabling cpuset in the child cgroups
+	 * will trigger a number of cpuset_attach() calls with no change
+	 * in effective cpus and mems. In that case, we can optimize out
+	 * by skipping the task iteration and update.
+	 */
+	if (cgroup_subsys_on_dfl(cpuset_cgrp_subsys) &&
+	    !cpus_updated && !mems_updated) {
+		cpuset_attach_nodemask_to = cs->effective_mems;
+		goto out;
+	}
+
+	guarantee_online_mems(cs, &cpuset_attach_nodemask_to);
+
+	cgroup_taskset_for_each(task, css, tset)
+		cpuset_attach_task(cs, task);
+
+	/*
+	 * Change mm for all threadgroup leaders. This is expensive and may
+	 * sleep and should be moved outside migration path proper. Skip it
+	 * if there is no change in effective_mems and CS_MEMORY_MIGRATE is
+	 * not set.
+	 */
+	cpuset_attach_nodemask_to = cs->effective_mems;
+	if (!is_memory_migrate(cs) && !mems_updated)
+		goto out;
+
+	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);
+		}
+	}
+
+out:
+	cs->old_mems_allowed = cpuset_attach_nodemask_to;
+
+	if (cs->nr_migrate_dl_tasks) {
+		cs->nr_deadline_tasks += cs->nr_migrate_dl_tasks;
+		oldcs->nr_deadline_tasks -= cs->nr_migrate_dl_tasks;
+		reset_migrate_dl_data(cs);
+	}
+
+	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_SUBPARTS_CPULIST,
+	FILE_CPU_EXCLUSIVE,
+	FILE_MEM_EXCLUSIVE,
+	FILE_MEM_HARDWALL,
+	FILE_SCHED_LOAD_BALANCE,
+	FILE_PARTITION_ROOT,
+	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;
+
+	cpus_read_lock();
+	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);
+	cpus_read_unlock();
+	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;
+
+	cpus_read_lock();
+	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);
+	cpus_read_unlock();
+	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);
+
+	cpus_read_lock();
+	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_cpuset(trialcs);
+out_unlock:
+	mutex_unlock(&cpuset_mutex);
+	cpus_read_unlock();
+	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;
+	case FILE_SUBPARTS_CPULIST:
+		seq_printf(sf, "%*pbl\n", cpumask_pr_args(cs->subparts_cpus));
+		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();
+	}
+
+	/* Unreachable but makes gcc happy */
+	return 0;
+}
+
+static int sched_partition_show(struct seq_file *seq, void *v)
+{
+	struct cpuset *cs = css_cs(seq_css(seq));
+	const char *err, *type = NULL;
+
+	switch (cs->partition_root_state) {
+	case PRS_ROOT:
+		seq_puts(seq, "root\n");
+		break;
+	case PRS_ISOLATED:
+		seq_puts(seq, "isolated\n");
+		break;
+	case PRS_MEMBER:
+		seq_puts(seq, "member\n");
+		break;
+	case PRS_INVALID_ROOT:
+		type = "root";
+		fallthrough;
+	case PRS_INVALID_ISOLATED:
+		if (!type)
+			type = "isolated";
+		err = perr_strings[READ_ONCE(cs->prs_err)];
+		if (err)
+			seq_printf(seq, "%s invalid (%s)\n", type, err);
+		else
+			seq_printf(seq, "%s invalid\n", type);
+		break;
+	}
+	return 0;
+}
+
+static ssize_t sched_partition_write(struct kernfs_open_file *of, char *buf,
+				     size_t nbytes, loff_t off)
+{
+	struct cpuset *cs = css_cs(of_css(of));
+	int val;
+	int retval = -ENODEV;
+
+	buf = strstrip(buf);
+
+	/*
+	 * Convert "root" to ENABLED, and convert "member" to DISABLED.
+	 */
+	if (!strcmp(buf, "root"))
+		val = PRS_ROOT;
+	else if (!strcmp(buf, "member"))
+		val = PRS_MEMBER;
+	else if (!strcmp(buf, "isolated"))
+		val = PRS_ISOLATED;
+	else
+		return -EINVAL;
+
+	css_get(&cs->css);
+	cpus_read_lock();
+	mutex_lock(&cpuset_mutex);
+	if (!is_cpuset_online(cs))
+		goto out_unlock;
+
+	retval = update_prstate(cs, val);
+out_unlock:
+	mutex_unlock(&cpuset_mutex);
+	cpus_read_unlock();
+	css_put(&cs->css);
+	return retval ?: nbytes;
+}
+
+/*
+ * for the common functions, 'private' gives the type of file
+ */
+
+static struct cftype legacy_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 */
+};
+
+/*
+ * This is currently a minimal set for the default hierarchy. It can be
+ * expanded later on by migrating more features and control files from v1.
+ */
+static struct cftype dfl_files[] = {
+	{
+		.name = "cpus",
+		.seq_show = cpuset_common_seq_show,
+		.write = cpuset_write_resmask,
+		.max_write_len = (100U + 6 * NR_CPUS),
+		.private = FILE_CPULIST,
+		.flags = CFTYPE_NOT_ON_ROOT,
+	},
+
+	{
+		.name = "mems",
+		.seq_show = cpuset_common_seq_show,
+		.write = cpuset_write_resmask,
+		.max_write_len = (100U + 6 * MAX_NUMNODES),
+		.private = FILE_MEMLIST,
+		.flags = CFTYPE_NOT_ON_ROOT,
+	},
+
+	{
+		.name = "cpus.effective",
+		.seq_show = cpuset_common_seq_show,
+		.private = FILE_EFFECTIVE_CPULIST,
+	},
+
+	{
+		.name = "mems.effective",
+		.seq_show = cpuset_common_seq_show,
+		.private = FILE_EFFECTIVE_MEMLIST,
+	},
+
+	{
+		.name = "cpus.partition",
+		.seq_show = sched_partition_show,
+		.write = sched_partition_write,
+		.private = FILE_PARTITION_ROOT,
+		.flags = CFTYPE_NOT_ON_ROOT,
+		.file_offset = offsetof(struct cpuset, partition_file),
+	},
+
+	{
+		.name = "cpus.subpartitions",
+		.seq_show = cpuset_common_seq_show,
+		.private = FILE_SUBPARTS_CPULIST,
+		.flags = CFTYPE_DEBUG,
+	},
+
+	{ }	/* terminate */
+};
+
+
+/**
+ * cpuset_css_alloc - Allocate a cpuset css
+ * @parent_css: Parent css of the control group that the new cpuset will be
+ *              part of
+ * Return: cpuset css on success, -ENOMEM on failure.
+ *
+ * Allocate and initialize a new cpuset css, for non-NULL @parent_css, return
+ * top cpuset css otherwise.
+ */
+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_cpumasks(cs, NULL)) {
+		kfree(cs);
+		return ERR_PTR(-ENOMEM);
+	}
+
+	__set_bit(CS_SCHED_LOAD_BALANCE, &cs->flags);
+	nodes_clear(cs->mems_allowed);
+	nodes_clear(cs->effective_mems);
+	fmeter_init(&cs->fmeter);
+	cs->relax_domain_level = -1;
+
+	/* Set CS_MEMORY_MIGRATE for default hierarchy */
+	if (cgroup_subsys_on_dfl(cpuset_cgrp_subsys))
+		__set_bit(CS_MEMORY_MIGRATE, &cs->flags);
+
+	return &cs->css;
+}
+
+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;
+
+	cpus_read_lock();
+	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;
+		cs->use_parent_ecpus = true;
+		parent->child_ecpus_count++;
+	}
+
+	/*
+	 * For v2, clear CS_SCHED_LOAD_BALANCE if parent is isolated
+	 */
+	if (cgroup_subsys_on_dfl(cpuset_cgrp_subsys) &&
+	    !is_sched_load_balance(parent))
+		clear_bit(CS_SCHED_LOAD_BALANCE, &cs->flags);
+
+	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
+	 * historical 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);
+	cpus_read_unlock();
+	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(). That is not needed
+ * in the default hierarchy where only changes in partition
+ * will cause repartitioning.
+ *
+ * If the cpuset has the 'sched.partition' flag enabled, simulate
+ * turning 'sched.partition" off.
+ */
+
+static void cpuset_css_offline(struct cgroup_subsys_state *css)
+{
+	struct cpuset *cs = css_cs(css);
+
+	cpus_read_lock();
+	mutex_lock(&cpuset_mutex);
+
+	if (is_partition_valid(cs))
+		update_prstate(cs, 0);
+
+	if (!cgroup_subsys_on_dfl(cpuset_cgrp_subsys) &&
+	    is_sched_load_balance(cs))
+		update_flag(CS_SCHED_LOAD_BALANCE, cs, 0);
+
+	if (cs->use_parent_ecpus) {
+		struct cpuset *parent = parent_cs(cs);
+
+		cs->use_parent_ecpus = false;
+		parent->child_ecpus_count--;
+	}
+
+	cpuset_dec();
+	clear_bit(CS_ONLINE, &cs->flags);
+
+	mutex_unlock(&cpuset_mutex);
+	cpus_read_unlock();
+}
+
+static void cpuset_css_free(struct cgroup_subsys_state *css)
+{
+	struct cpuset *cs = css_cs(css);
+
+	free_cpuset(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);
+}
+
+/*
+ * In case the child is cloned into a cpuset different from its parent,
+ * additional checks are done to see if the move is allowed.
+ */
+static int cpuset_can_fork(struct task_struct *task, struct css_set *cset)
+{
+	struct cpuset *cs = css_cs(cset->subsys[cpuset_cgrp_id]);
+	bool same_cs;
+	int ret;
+
+	rcu_read_lock();
+	same_cs = (cs == task_cs(current));
+	rcu_read_unlock();
+
+	if (same_cs)
+		return 0;
+
+	lockdep_assert_held(&cgroup_mutex);
+	mutex_lock(&cpuset_mutex);
+
+	/* Check to see if task is allowed in the cpuset */
+	ret = cpuset_can_attach_check(cs);
+	if (ret)
+		goto out_unlock;
+
+	ret = task_can_attach(task);
+	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++;
+out_unlock:
+	mutex_unlock(&cpuset_mutex);
+	return ret;
+}
+
+static void cpuset_cancel_fork(struct task_struct *task, struct css_set *cset)
+{
+	struct cpuset *cs = css_cs(cset->subsys[cpuset_cgrp_id]);
+	bool same_cs;
+
+	rcu_read_lock();
+	same_cs = (cs == task_cs(current));
+	rcu_read_unlock();
+
+	if (same_cs)
+		return;
+
+	mutex_lock(&cpuset_mutex);
+	cs->attach_in_progress--;
+	if (!cs->attach_in_progress)
+		wake_up(&cpuset_attach_wq);
+	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)
+{
+	struct cpuset *cs;
+	bool same_cs;
+
+	rcu_read_lock();
+	cs = task_cs(task);
+	same_cs = (cs == task_cs(current));
+	rcu_read_unlock();
+
+	if (same_cs) {
+		if (cs == &top_cpuset)
+			return;
+
+		set_cpus_allowed_ptr(task, current->cpus_ptr);
+		task->mems_allowed = current->mems_allowed;
+		return;
+	}
+
+	/* CLONE_INTO_CGROUP */
+	mutex_lock(&cpuset_mutex);
+	guarantee_online_mems(cs, &cpuset_attach_nodemask_to);
+	cpuset_attach_task(cs, task);
+
+	cs->attach_in_progress--;
+	if (!cs->attach_in_progress)
+		wake_up(&cpuset_attach_wq);
+
+	mutex_unlock(&cpuset_mutex);
+}
+
+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,
+	.can_fork	= cpuset_can_fork,
+	.cancel_fork	= cpuset_cancel_fork,
+	.fork		= cpuset_fork,
+	.legacy_cftypes	= legacy_files,
+	.dfl_cftypes	= dfl_files,
+	.early_init	= true,
+	.threaded	= true,
+};
+
+/**
+ * cpuset_init - initialize cpusets at system boot
+ *
+ * Description: Initialize top_cpuset
+ **/
+
+int __init cpuset_init(void)
+{
+	BUG_ON(!alloc_cpumask_var(&top_cpuset.cpus_allowed, GFP_KERNEL));
+	BUG_ON(!alloc_cpumask_var(&top_cpuset.effective_cpus, GFP_KERNEL));
+	BUG_ON(!zalloc_cpumask_var(&top_cpuset.subparts_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;
+
+	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 migrated to an ancestor.
+	 */
+	if (cpus_updated && !cpumask_empty(cs->cpus_allowed))
+		update_tasks_cpumask(cs, new_cpus);
+	if (mems_updated && !nodes_empty(cs->mems_allowed))
+		update_tasks_nodemask(cs);
+
+	is_empty = cpumask_empty(cs->cpus_allowed) ||
+		   nodes_empty(cs->mems_allowed);
+
+	/*
+	 * 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) {
+		mutex_unlock(&cpuset_mutex);
+		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)
+{
+	/* A partition root is allowed to have empty effective cpus */
+	if (cpumask_empty(new_cpus) && !is_partition_valid(cs))
+		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, new_cpus);
+	if (mems_updated)
+		update_tasks_nodemask(cs);
+}
+
+static bool force_rebuild;
+
+void cpuset_force_rebuild(void)
+{
+	force_rebuild = true;
+}
+
+/**
+ * cpuset_hotplug_update_tasks - update tasks in a cpuset for hotunplug
+ * @cs: cpuset in interest
+ * @tmp: the tmpmasks structure pointer
+ *
+ * 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, struct tmpmasks *tmp)
+{
+	static cpumask_t new_cpus;
+	static nodemask_t new_mems;
+	bool cpus_updated;
+	bool mems_updated;
+	struct cpuset *parent;
+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;
+	}
+
+	parent = parent_cs(cs);
+	compute_effective_cpumask(&new_cpus, cs, parent);
+	nodes_and(new_mems, cs->mems_allowed, parent->effective_mems);
+
+	if (cs->nr_subparts_cpus)
+		/*
+		 * Make sure that CPUs allocated to child partitions
+		 * do not show up in effective_cpus.
+		 */
+		cpumask_andnot(&new_cpus, &new_cpus, cs->subparts_cpus);
+
+	if (!tmp || !cs->partition_root_state)
+		goto update_tasks;
+
+	/*
+	 * In the unlikely event that a partition root has empty
+	 * effective_cpus with tasks, we will have to invalidate child
+	 * partitions, if present, by setting nr_subparts_cpus to 0 to
+	 * reclaim their cpus.
+	 */
+	if (cs->nr_subparts_cpus && is_partition_valid(cs) &&
+	    cpumask_empty(&new_cpus) && partition_is_populated(cs, NULL)) {
+		spin_lock_irq(&callback_lock);
+		cs->nr_subparts_cpus = 0;
+		cpumask_clear(cs->subparts_cpus);
+		spin_unlock_irq(&callback_lock);
+		compute_effective_cpumask(&new_cpus, cs, parent);
+	}
+
+	/*
+	 * Force the partition to become invalid if either one of
+	 * the following conditions hold:
+	 * 1) empty effective cpus but not valid empty partition.
+	 * 2) parent is invalid or doesn't grant any cpus to child
+	 *    partitions.
+	 */
+	if (is_partition_valid(cs) && (!parent->nr_subparts_cpus ||
+	   (cpumask_empty(&new_cpus) && partition_is_populated(cs, NULL)))) {
+		int old_prs, parent_prs;
+
+		update_parent_subparts_cpumask(cs, partcmd_disable, NULL, tmp);
+		if (cs->nr_subparts_cpus) {
+			spin_lock_irq(&callback_lock);
+			cs->nr_subparts_cpus = 0;
+			cpumask_clear(cs->subparts_cpus);
+			spin_unlock_irq(&callback_lock);
+			compute_effective_cpumask(&new_cpus, cs, parent);
+		}
+
+		old_prs = cs->partition_root_state;
+		parent_prs = parent->partition_root_state;
+		if (is_partition_valid(cs)) {
+			spin_lock_irq(&callback_lock);
+			make_partition_invalid(cs);
+			spin_unlock_irq(&callback_lock);
+			if (is_prs_invalid(parent_prs))
+				WRITE_ONCE(cs->prs_err, PERR_INVPARENT);
+			else if (!parent_prs)
+				WRITE_ONCE(cs->prs_err, PERR_NOTPART);
+			else
+				WRITE_ONCE(cs->prs_err, PERR_HOTPLUG);
+			notify_partition_change(cs, old_prs);
+		}
+		cpuset_force_rebuild();
+	}
+
+	/*
+	 * On the other hand, an invalid partition root may be transitioned
+	 * back to a regular one.
+	 */
+	else if (is_partition_valid(parent) && is_partition_invalid(cs)) {
+		update_parent_subparts_cpumask(cs, partcmd_update, NULL, tmp);
+		if (is_partition_valid(cs))
+			cpuset_force_rebuild();
+	}
+
+update_tasks:
+	cpus_updated = !cpumask_equal(&new_cpus, cs->effective_cpus);
+	mems_updated = !nodes_equal(new_mems, cs->effective_mems);
+	if (!cpus_updated && !mems_updated)
+		goto unlock;	/* Hotplug doesn't affect this cpuset */
+
+	if (mems_updated)
+		check_insane_mems_config(&new_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);
+
+unlock:
+	mutex_unlock(&cpuset_mutex);
+}
+
+/**
+ * cpuset_hotplug_workfn - handle CPU/memory hotunplug for a cpuset
+ * @work: unused
+ *
+ * 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();
+	struct tmpmasks tmp, *ptmp = NULL;
+
+	if (on_dfl && !alloc_cpumasks(NULL, &tmp))
+		ptmp = &tmp;
+
+	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];
+
+	/*
+	 * If subparts_cpus is populated, it is likely that the check below
+	 * will produce a false positive on cpus_updated when the cpu list
+	 * isn't changed. It is extra work, but it is better to be safe.
+	 */
+	cpus_updated = !cpumask_equal(top_cpuset.effective_cpus, &new_cpus);
+	mems_updated = !nodes_equal(top_cpuset.effective_mems, new_mems);
+
+	/*
+	 * In the rare case that hotplug removes all the cpus in subparts_cpus,
+	 * we assumed that cpus are updated.
+	 */
+	if (!cpus_updated && top_cpuset.nr_subparts_cpus)
+		cpus_updated = true;
+
+	/* 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);
+		/*
+		 * Make sure that CPUs allocated to child partitions
+		 * do not show up in effective_cpus. If no CPU is left,
+		 * we clear the subparts_cpus & let the child partitions
+		 * fight for the CPUs again.
+		 */
+		if (top_cpuset.nr_subparts_cpus) {
+			if (cpumask_subset(&new_cpus,
+					   top_cpuset.subparts_cpus)) {
+				top_cpuset.nr_subparts_cpus = 0;
+				cpumask_clear(top_cpuset.subparts_cpus);
+			} else {
+				cpumask_andnot(&new_cpus, &new_cpus,
+					       top_cpuset.subparts_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, ptmp);
+
+			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();
+	}
+
+	free_cpumasks(NULL, ptmp);
+}
+
+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;
+}
+
+/**
+ * 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];
+
+	hotplug_memory_notifier(cpuset_track_online_nodes, CPUSET_CALLBACK_PRI);
+
+	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, except when the task is in the top cpuset.
+ **/
+
+void cpuset_cpus_allowed(struct task_struct *tsk, struct cpumask *pmask)
+{
+	unsigned long flags;
+	struct cpuset *cs;
+
+	spin_lock_irqsave(&callback_lock, flags);
+	rcu_read_lock();
+
+	cs = task_cs(tsk);
+	if (cs != &top_cpuset)
+		guarantee_online_cpus(tsk, pmask);
+	/*
+	 * Tasks in the top cpuset won't get update to their cpumasks
+	 * when a hotplug online/offline event happens. So we include all
+	 * offline cpus in the allowed cpu list.
+	 */
+	if ((cs == &top_cpuset) || cpumask_empty(pmask)) {
+		const struct cpumask *possible_mask = task_cpu_possible_mask(tsk);
+
+		/*
+		 * We first exclude cpus allocated to partitions. If there is no
+		 * allowable online cpu left, we fall back to all possible cpus.
+		 */
+		cpumask_andnot(pmask, possible_mask, top_cpuset.subparts_cpus);
+		if (!cpumask_intersects(pmask, cpu_online_mask))
+			cpumask_copy(pmask, possible_mask);
+	}
+
+	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.
+ *
+ * Returns true if the affinity of @tsk was changed, false otherwise.
+ **/
+
+bool cpuset_cpus_allowed_fallback(struct task_struct *tsk)
+{
+	const struct cpumask *possible_mask = task_cpu_possible_mask(tsk);
+	const struct cpumask *cs_mask;
+	bool changed = false;
+
+	rcu_read_lock();
+	cs_mask = task_cs(tsk)->cpus_allowed;
+	if (is_in_v2_mode() && cpumask_subset(cs_mask, possible_mask)) {
+		do_set_cpus_allowed(tsk, cs_mask);
+		changed = true;
+	}
+	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.
+	 */
+	return changed;
+}
+
+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. current 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 */
+	bool 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_spread_node() - On which node to begin search for a page
+ * @rotor: round robin rotor
+ *
+ * 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);
+}
+
+/**
+ * cpuset_mem_spread_node() - On which node to begin search for a file page
+ */
+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);
+}
+
+/**
+ * cpuset_slab_spread_node() - On which node to begin search for a slab page
+ */
+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_cont(",cpuset=");
+	pr_cont_cgroup_name(cgrp);
+	pr_cont(",mems_allowed=%*pbl",
+		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));
+}