Adding upstream version 6.6.15.upstream/6.6.15

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

1 files changed, 1534 insertions, 0 deletions

diff --git a/kernel/kthread.c b/kernel/kthread.c
new file mode 100644
index 0000000000..1eea53050b
--- /dev/null
+++ b/kernel/kthread.c
@@ -0,0 +1,1534 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Kernel thread helper functions.
+ *   Copyright (C) 2004 IBM Corporation, Rusty Russell.
+ *   Copyright (C) 2009 Red Hat, Inc.
+ *
+ * Creation is done via kthreadd, so that we get a clean environment
+ * even if we're invoked from userspace (think modprobe, hotplug cpu,
+ * etc.).
+ */
+#include <uapi/linux/sched/types.h>
+#include <linux/mm.h>
+#include <linux/mmu_context.h>
+#include <linux/sched.h>
+#include <linux/sched/mm.h>
+#include <linux/sched/task.h>
+#include <linux/kthread.h>
+#include <linux/completion.h>
+#include <linux/err.h>
+#include <linux/cgroup.h>
+#include <linux/cpuset.h>
+#include <linux/unistd.h>
+#include <linux/file.h>
+#include <linux/export.h>
+#include <linux/mutex.h>
+#include <linux/slab.h>
+#include <linux/freezer.h>
+#include <linux/ptrace.h>
+#include <linux/uaccess.h>
+#include <linux/numa.h>
+#include <linux/sched/isolation.h>
+#include <trace/events/sched.h>
+
+
+static DEFINE_SPINLOCK(kthread_create_lock);
+static LIST_HEAD(kthread_create_list);
+struct task_struct *kthreadd_task;
+
+struct kthread_create_info
+{
+	/* Information passed to kthread() from kthreadd. */
+	char *full_name;
+	int (*threadfn)(void *data);
+	void *data;
+	int node;
+
+	/* Result passed back to kthread_create() from kthreadd. */
+	struct task_struct *result;
+	struct completion *done;
+
+	struct list_head list;
+};
+
+struct kthread {
+	unsigned long flags;
+	unsigned int cpu;
+	int result;
+	int (*threadfn)(void *);
+	void *data;
+	struct completion parked;
+	struct completion exited;
+#ifdef CONFIG_BLK_CGROUP
+	struct cgroup_subsys_state *blkcg_css;
+#endif
+	/* To store the full name if task comm is truncated. */
+	char *full_name;
+};
+
+enum KTHREAD_BITS {
+	KTHREAD_IS_PER_CPU = 0,
+	KTHREAD_SHOULD_STOP,
+	KTHREAD_SHOULD_PARK,
+};
+
+static inline struct kthread *to_kthread(struct task_struct *k)
+{
+	WARN_ON(!(k->flags & PF_KTHREAD));
+	return k->worker_private;
+}
+
+/*
+ * Variant of to_kthread() that doesn't assume @p is a kthread.
+ *
+ * Per construction; when:
+ *
+ *   (p->flags & PF_KTHREAD) && p->worker_private
+ *
+ * the task is both a kthread and struct kthread is persistent. However
+ * PF_KTHREAD on it's own is not, kernel_thread() can exec() (See umh.c and
+ * begin_new_exec()).
+ */
+static inline struct kthread *__to_kthread(struct task_struct *p)
+{
+	void *kthread = p->worker_private;
+	if (kthread && !(p->flags & PF_KTHREAD))
+		kthread = NULL;
+	return kthread;
+}
+
+void get_kthread_comm(char *buf, size_t buf_size, struct task_struct *tsk)
+{
+	struct kthread *kthread = to_kthread(tsk);
+
+	if (!kthread || !kthread->full_name) {
+		__get_task_comm(buf, buf_size, tsk);
+		return;
+	}
+
+	strscpy_pad(buf, kthread->full_name, buf_size);
+}
+
+bool set_kthread_struct(struct task_struct *p)
+{
+	struct kthread *kthread;
+
+	if (WARN_ON_ONCE(to_kthread(p)))
+		return false;
+
+	kthread = kzalloc(sizeof(*kthread), GFP_KERNEL);
+	if (!kthread)
+		return false;
+
+	init_completion(&kthread->exited);
+	init_completion(&kthread->parked);
+	p->vfork_done = &kthread->exited;
+
+	p->worker_private = kthread;
+	return true;
+}
+
+void free_kthread_struct(struct task_struct *k)
+{
+	struct kthread *kthread;
+
+	/*
+	 * Can be NULL if kmalloc() in set_kthread_struct() failed.
+	 */
+	kthread = to_kthread(k);
+	if (!kthread)
+		return;
+
+#ifdef CONFIG_BLK_CGROUP
+	WARN_ON_ONCE(kthread->blkcg_css);
+#endif
+	k->worker_private = NULL;
+	kfree(kthread->full_name);
+	kfree(kthread);
+}
+
+/**
+ * kthread_should_stop - should this kthread return now?
+ *
+ * When someone calls kthread_stop() on your kthread, it will be woken
+ * and this will return true.  You should then return, and your return
+ * value will be passed through to kthread_stop().
+ */
+bool kthread_should_stop(void)
+{
+	return test_bit(KTHREAD_SHOULD_STOP, &to_kthread(current)->flags);
+}
+EXPORT_SYMBOL(kthread_should_stop);
+
+static bool __kthread_should_park(struct task_struct *k)
+{
+	return test_bit(KTHREAD_SHOULD_PARK, &to_kthread(k)->flags);
+}
+
+/**
+ * kthread_should_park - should this kthread park now?
+ *
+ * When someone calls kthread_park() on your kthread, it will be woken
+ * and this will return true.  You should then do the necessary
+ * cleanup and call kthread_parkme()
+ *
+ * Similar to kthread_should_stop(), but this keeps the thread alive
+ * and in a park position. kthread_unpark() "restarts" the thread and
+ * calls the thread function again.
+ */
+bool kthread_should_park(void)
+{
+	return __kthread_should_park(current);
+}
+EXPORT_SYMBOL_GPL(kthread_should_park);
+
+bool kthread_should_stop_or_park(void)
+{
+	struct kthread *kthread = __to_kthread(current);
+
+	if (!kthread)
+		return false;
+
+	return kthread->flags & (BIT(KTHREAD_SHOULD_STOP) | BIT(KTHREAD_SHOULD_PARK));
+}
+
+/**
+ * kthread_freezable_should_stop - should this freezable kthread return now?
+ * @was_frozen: optional out parameter, indicates whether %current was frozen
+ *
+ * kthread_should_stop() for freezable kthreads, which will enter
+ * refrigerator if necessary.  This function is safe from kthread_stop() /
+ * freezer deadlock and freezable kthreads should use this function instead
+ * of calling try_to_freeze() directly.
+ */
+bool kthread_freezable_should_stop(bool *was_frozen)
+{
+	bool frozen = false;
+
+	might_sleep();
+
+	if (unlikely(freezing(current)))
+		frozen = __refrigerator(true);
+
+	if (was_frozen)
+		*was_frozen = frozen;
+
+	return kthread_should_stop();
+}
+EXPORT_SYMBOL_GPL(kthread_freezable_should_stop);
+
+/**
+ * kthread_func - return the function specified on kthread creation
+ * @task: kthread task in question
+ *
+ * Returns NULL if the task is not a kthread.
+ */
+void *kthread_func(struct task_struct *task)
+{
+	struct kthread *kthread = __to_kthread(task);
+	if (kthread)
+		return kthread->threadfn;
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(kthread_func);
+
+/**
+ * kthread_data - return data value specified on kthread creation
+ * @task: kthread task in question
+ *
+ * Return the data value specified when kthread @task was created.
+ * The caller is responsible for ensuring the validity of @task when
+ * calling this function.
+ */
+void *kthread_data(struct task_struct *task)
+{
+	return to_kthread(task)->data;
+}
+EXPORT_SYMBOL_GPL(kthread_data);
+
+/**
+ * kthread_probe_data - speculative version of kthread_data()
+ * @task: possible kthread task in question
+ *
+ * @task could be a kthread task.  Return the data value specified when it
+ * was created if accessible.  If @task isn't a kthread task or its data is
+ * inaccessible for any reason, %NULL is returned.  This function requires
+ * that @task itself is safe to dereference.
+ */
+void *kthread_probe_data(struct task_struct *task)
+{
+	struct kthread *kthread = __to_kthread(task);
+	void *data = NULL;
+
+	if (kthread)
+		copy_from_kernel_nofault(&data, &kthread->data, sizeof(data));
+	return data;
+}
+
+static void __kthread_parkme(struct kthread *self)
+{
+	for (;;) {
+		/*
+		 * TASK_PARKED is a special state; we must serialize against
+		 * possible pending wakeups to avoid store-store collisions on
+		 * task->state.
+		 *
+		 * Such a collision might possibly result in the task state
+		 * changin from TASK_PARKED and us failing the
+		 * wait_task_inactive() in kthread_park().
+		 */
+		set_special_state(TASK_PARKED);
+		if (!test_bit(KTHREAD_SHOULD_PARK, &self->flags))
+			break;
+
+		/*
+		 * Thread is going to call schedule(), do not preempt it,
+		 * or the caller of kthread_park() may spend more time in
+		 * wait_task_inactive().
+		 */
+		preempt_disable();
+		complete(&self->parked);
+		schedule_preempt_disabled();
+		preempt_enable();
+	}
+	__set_current_state(TASK_RUNNING);
+}
+
+void kthread_parkme(void)
+{
+	__kthread_parkme(to_kthread(current));
+}
+EXPORT_SYMBOL_GPL(kthread_parkme);
+
+/**
+ * kthread_exit - Cause the current kthread return @result to kthread_stop().
+ * @result: The integer value to return to kthread_stop().
+ *
+ * While kthread_exit can be called directly, it exists so that
+ * functions which do some additional work in non-modular code such as
+ * module_put_and_kthread_exit can be implemented.
+ *
+ * Does not return.
+ */
+void __noreturn kthread_exit(long result)
+{
+	struct kthread *kthread = to_kthread(current);
+	kthread->result = result;
+	do_exit(0);
+}
+
+/**
+ * kthread_complete_and_exit - Exit the current kthread.
+ * @comp: Completion to complete
+ * @code: The integer value to return to kthread_stop().
+ *
+ * If present, complete @comp and then return code to kthread_stop().
+ *
+ * A kernel thread whose module may be removed after the completion of
+ * @comp can use this function to exit safely.
+ *
+ * Does not return.
+ */
+void __noreturn kthread_complete_and_exit(struct completion *comp, long code)
+{
+	if (comp)
+		complete(comp);
+
+	kthread_exit(code);
+}
+EXPORT_SYMBOL(kthread_complete_and_exit);
+
+static int kthread(void *_create)
+{
+	static const struct sched_param param = { .sched_priority = 0 };
+	/* Copy data: it's on kthread's stack */
+	struct kthread_create_info *create = _create;
+	int (*threadfn)(void *data) = create->threadfn;
+	void *data = create->data;
+	struct completion *done;
+	struct kthread *self;
+	int ret;
+
+	self = to_kthread(current);
+
+	/* Release the structure when caller killed by a fatal signal. */
+	done = xchg(&create->done, NULL);
+	if (!done) {
+		kfree(create->full_name);
+		kfree(create);
+		kthread_exit(-EINTR);
+	}
+
+	self->full_name = create->full_name;
+	self->threadfn = threadfn;
+	self->data = data;
+
+	/*
+	 * The new thread inherited kthreadd's priority and CPU mask. Reset
+	 * back to default in case they have been changed.
+	 */
+	sched_setscheduler_nocheck(current, SCHED_NORMAL, &param);
+	set_cpus_allowed_ptr(current, housekeeping_cpumask(HK_TYPE_KTHREAD));
+
+	/* OK, tell user we're spawned, wait for stop or wakeup */
+	__set_current_state(TASK_UNINTERRUPTIBLE);
+	create->result = current;
+	/*
+	 * Thread is going to call schedule(), do not preempt it,
+	 * or the creator may spend more time in wait_task_inactive().
+	 */
+	preempt_disable();
+	complete(done);
+	schedule_preempt_disabled();
+	preempt_enable();
+
+	ret = -EINTR;
+	if (!test_bit(KTHREAD_SHOULD_STOP, &self->flags)) {
+		cgroup_kthread_ready();
+		__kthread_parkme(self);
+		ret = threadfn(data);
+	}
+	kthread_exit(ret);
+}
+
+/* called from kernel_clone() to get node information for about to be created task */
+int tsk_fork_get_node(struct task_struct *tsk)
+{
+#ifdef CONFIG_NUMA
+	if (tsk == kthreadd_task)
+		return tsk->pref_node_fork;
+#endif
+	return NUMA_NO_NODE;
+}
+
+static void create_kthread(struct kthread_create_info *create)
+{
+	int pid;
+
+#ifdef CONFIG_NUMA
+	current->pref_node_fork = create->node;
+#endif
+	/* We want our own signal handler (we take no signals by default). */
+	pid = kernel_thread(kthread, create, create->full_name,
+			    CLONE_FS | CLONE_FILES | SIGCHLD);
+	if (pid < 0) {
+		/* Release the structure when caller killed by a fatal signal. */
+		struct completion *done = xchg(&create->done, NULL);
+
+		kfree(create->full_name);
+		if (!done) {
+			kfree(create);
+			return;
+		}
+		create->result = ERR_PTR(pid);
+		complete(done);
+	}
+}
+
+static __printf(4, 0)
+struct task_struct *__kthread_create_on_node(int (*threadfn)(void *data),
+						    void *data, int node,
+						    const char namefmt[],
+						    va_list args)
+{
+	DECLARE_COMPLETION_ONSTACK(done);
+	struct task_struct *task;
+	struct kthread_create_info *create = kmalloc(sizeof(*create),
+						     GFP_KERNEL);
+
+	if (!create)
+		return ERR_PTR(-ENOMEM);
+	create->threadfn = threadfn;
+	create->data = data;
+	create->node = node;
+	create->done = &done;
+	create->full_name = kvasprintf(GFP_KERNEL, namefmt, args);
+	if (!create->full_name) {
+		task = ERR_PTR(-ENOMEM);
+		goto free_create;
+	}
+
+	spin_lock(&kthread_create_lock);
+	list_add_tail(&create->list, &kthread_create_list);
+	spin_unlock(&kthread_create_lock);
+
+	wake_up_process(kthreadd_task);
+	/*
+	 * Wait for completion in killable state, for I might be chosen by
+	 * the OOM killer while kthreadd is trying to allocate memory for
+	 * new kernel thread.
+	 */
+	if (unlikely(wait_for_completion_killable(&done))) {
+		/*
+		 * If I was killed by a fatal signal before kthreadd (or new
+		 * kernel thread) calls complete(), leave the cleanup of this
+		 * structure to that thread.
+		 */
+		if (xchg(&create->done, NULL))
+			return ERR_PTR(-EINTR);
+		/*
+		 * kthreadd (or new kernel thread) will call complete()
+		 * shortly.
+		 */
+		wait_for_completion(&done);
+	}
+	task = create->result;
+free_create:
+	kfree(create);
+	return task;
+}
+
+/**
+ * kthread_create_on_node - create a kthread.
+ * @threadfn: the function to run until signal_pending(current).
+ * @data: data ptr for @threadfn.
+ * @node: task and thread structures for the thread are allocated on this node
+ * @namefmt: printf-style name for the thread.
+ *
+ * Description: This helper function creates and names a kernel
+ * thread.  The thread will be stopped: use wake_up_process() to start
+ * it.  See also kthread_run().  The new thread has SCHED_NORMAL policy and
+ * is affine to all CPUs.
+ *
+ * If thread is going to be bound on a particular cpu, give its node
+ * in @node, to get NUMA affinity for kthread stack, or else give NUMA_NO_NODE.
+ * When woken, the thread will run @threadfn() with @data as its
+ * argument. @threadfn() can either return directly if it is a
+ * standalone thread for which no one will call kthread_stop(), or
+ * return when 'kthread_should_stop()' is true (which means
+ * kthread_stop() has been called).  The return value should be zero
+ * or a negative error number; it will be passed to kthread_stop().
+ *
+ * Returns a task_struct or ERR_PTR(-ENOMEM) or ERR_PTR(-EINTR).
+ */
+struct task_struct *kthread_create_on_node(int (*threadfn)(void *data),
+					   void *data, int node,
+					   const char namefmt[],
+					   ...)
+{
+	struct task_struct *task;
+	va_list args;
+
+	va_start(args, namefmt);
+	task = __kthread_create_on_node(threadfn, data, node, namefmt, args);
+	va_end(args);
+
+	return task;
+}
+EXPORT_SYMBOL(kthread_create_on_node);
+
+static void __kthread_bind_mask(struct task_struct *p, const struct cpumask *mask, unsigned int state)
+{
+	unsigned long flags;
+
+	if (!wait_task_inactive(p, state)) {
+		WARN_ON(1);
+		return;
+	}
+
+	/* It's safe because the task is inactive. */
+	raw_spin_lock_irqsave(&p->pi_lock, flags);
+	do_set_cpus_allowed(p, mask);
+	p->flags |= PF_NO_SETAFFINITY;
+	raw_spin_unlock_irqrestore(&p->pi_lock, flags);
+}
+
+static void __kthread_bind(struct task_struct *p, unsigned int cpu, unsigned int state)
+{
+	__kthread_bind_mask(p, cpumask_of(cpu), state);
+}
+
+void kthread_bind_mask(struct task_struct *p, const struct cpumask *mask)
+{
+	__kthread_bind_mask(p, mask, TASK_UNINTERRUPTIBLE);
+}
+
+/**
+ * kthread_bind - bind a just-created kthread to a cpu.
+ * @p: thread created by kthread_create().
+ * @cpu: cpu (might not be online, must be possible) for @k to run on.
+ *
+ * Description: This function is equivalent to set_cpus_allowed(),
+ * except that @cpu doesn't need to be online, and the thread must be
+ * stopped (i.e., just returned from kthread_create()).
+ */
+void kthread_bind(struct task_struct *p, unsigned int cpu)
+{
+	__kthread_bind(p, cpu, TASK_UNINTERRUPTIBLE);
+}
+EXPORT_SYMBOL(kthread_bind);
+
+/**
+ * kthread_create_on_cpu - Create a cpu bound kthread
+ * @threadfn: the function to run until signal_pending(current).
+ * @data: data ptr for @threadfn.
+ * @cpu: The cpu on which the thread should be bound,
+ * @namefmt: printf-style name for the thread. Format is restricted
+ *	     to "name.*%u". Code fills in cpu number.
+ *
+ * Description: This helper function creates and names a kernel thread
+ */
+struct task_struct *kthread_create_on_cpu(int (*threadfn)(void *data),
+					  void *data, unsigned int cpu,
+					  const char *namefmt)
+{
+	struct task_struct *p;
+
+	p = kthread_create_on_node(threadfn, data, cpu_to_node(cpu), namefmt,
+				   cpu);
+	if (IS_ERR(p))
+		return p;
+	kthread_bind(p, cpu);
+	/* CPU hotplug need to bind once again when unparking the thread. */
+	to_kthread(p)->cpu = cpu;
+	return p;
+}
+EXPORT_SYMBOL(kthread_create_on_cpu);
+
+void kthread_set_per_cpu(struct task_struct *k, int cpu)
+{
+	struct kthread *kthread = to_kthread(k);
+	if (!kthread)
+		return;
+
+	WARN_ON_ONCE(!(k->flags & PF_NO_SETAFFINITY));
+
+	if (cpu < 0) {
+		clear_bit(KTHREAD_IS_PER_CPU, &kthread->flags);
+		return;
+	}
+
+	kthread->cpu = cpu;
+	set_bit(KTHREAD_IS_PER_CPU, &kthread->flags);
+}
+
+bool kthread_is_per_cpu(struct task_struct *p)
+{
+	struct kthread *kthread = __to_kthread(p);
+	if (!kthread)
+		return false;
+
+	return test_bit(KTHREAD_IS_PER_CPU, &kthread->flags);
+}
+
+/**
+ * kthread_unpark - unpark a thread created by kthread_create().
+ * @k:		thread created by kthread_create().
+ *
+ * Sets kthread_should_park() for @k to return false, wakes it, and
+ * waits for it to return. If the thread is marked percpu then its
+ * bound to the cpu again.
+ */
+void kthread_unpark(struct task_struct *k)
+{
+	struct kthread *kthread = to_kthread(k);
+
+	/*
+	 * Newly created kthread was parked when the CPU was offline.
+	 * The binding was lost and we need to set it again.
+	 */
+	if (test_bit(KTHREAD_IS_PER_CPU, &kthread->flags))
+		__kthread_bind(k, kthread->cpu, TASK_PARKED);
+
+	clear_bit(KTHREAD_SHOULD_PARK, &kthread->flags);
+	/*
+	 * __kthread_parkme() will either see !SHOULD_PARK or get the wakeup.
+	 */
+	wake_up_state(k, TASK_PARKED);
+}
+EXPORT_SYMBOL_GPL(kthread_unpark);
+
+/**
+ * kthread_park - park a thread created by kthread_create().
+ * @k: thread created by kthread_create().
+ *
+ * Sets kthread_should_park() for @k to return true, wakes it, and
+ * waits for it to return. This can also be called after kthread_create()
+ * instead of calling wake_up_process(): the thread will park without
+ * calling threadfn().
+ *
+ * Returns 0 if the thread is parked, -ENOSYS if the thread exited.
+ * If called by the kthread itself just the park bit is set.
+ */
+int kthread_park(struct task_struct *k)
+{
+	struct kthread *kthread = to_kthread(k);
+
+	if (WARN_ON(k->flags & PF_EXITING))
+		return -ENOSYS;
+
+	if (WARN_ON_ONCE(test_bit(KTHREAD_SHOULD_PARK, &kthread->flags)))
+		return -EBUSY;
+
+	set_bit(KTHREAD_SHOULD_PARK, &kthread->flags);
+	if (k != current) {
+		wake_up_process(k);
+		/*
+		 * Wait for __kthread_parkme() to complete(), this means we
+		 * _will_ have TASK_PARKED and are about to call schedule().
+		 */
+		wait_for_completion(&kthread->parked);
+		/*
+		 * Now wait for that schedule() to complete and the task to
+		 * get scheduled out.
+		 */
+		WARN_ON_ONCE(!wait_task_inactive(k, TASK_PARKED));
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(kthread_park);
+
+/**
+ * kthread_stop - stop a thread created by kthread_create().
+ * @k: thread created by kthread_create().
+ *
+ * Sets kthread_should_stop() for @k to return true, wakes it, and
+ * waits for it to exit. This can also be called after kthread_create()
+ * instead of calling wake_up_process(): the thread will exit without
+ * calling threadfn().
+ *
+ * If threadfn() may call kthread_exit() itself, the caller must ensure
+ * task_struct can't go away.
+ *
+ * Returns the result of threadfn(), or %-EINTR if wake_up_process()
+ * was never called.
+ */
+int kthread_stop(struct task_struct *k)
+{
+	struct kthread *kthread;
+	int ret;
+
+	trace_sched_kthread_stop(k);
+
+	get_task_struct(k);
+	kthread = to_kthread(k);
+	set_bit(KTHREAD_SHOULD_STOP, &kthread->flags);
+	kthread_unpark(k);
+	set_tsk_thread_flag(k, TIF_NOTIFY_SIGNAL);
+	wake_up_process(k);
+	wait_for_completion(&kthread->exited);
+	ret = kthread->result;
+	put_task_struct(k);
+
+	trace_sched_kthread_stop_ret(ret);
+	return ret;
+}
+EXPORT_SYMBOL(kthread_stop);
+
+int kthreadd(void *unused)
+{
+	struct task_struct *tsk = current;
+
+	/* Setup a clean context for our children to inherit. */
+	set_task_comm(tsk, "kthreadd");
+	ignore_signals(tsk);
+	set_cpus_allowed_ptr(tsk, housekeeping_cpumask(HK_TYPE_KTHREAD));
+	set_mems_allowed(node_states[N_MEMORY]);
+
+	current->flags |= PF_NOFREEZE;
+	cgroup_init_kthreadd();
+
+	for (;;) {
+		set_current_state(TASK_INTERRUPTIBLE);
+		if (list_empty(&kthread_create_list))
+			schedule();
+		__set_current_state(TASK_RUNNING);
+
+		spin_lock(&kthread_create_lock);
+		while (!list_empty(&kthread_create_list)) {
+			struct kthread_create_info *create;
+
+			create = list_entry(kthread_create_list.next,
+					    struct kthread_create_info, list);
+			list_del_init(&create->list);
+			spin_unlock(&kthread_create_lock);
+
+			create_kthread(create);
+
+			spin_lock(&kthread_create_lock);
+		}
+		spin_unlock(&kthread_create_lock);
+	}
+
+	return 0;
+}
+
+void __kthread_init_worker(struct kthread_worker *worker,
+				const char *name,
+				struct lock_class_key *key)
+{
+	memset(worker, 0, sizeof(struct kthread_worker));
+	raw_spin_lock_init(&worker->lock);
+	lockdep_set_class_and_name(&worker->lock, key, name);
+	INIT_LIST_HEAD(&worker->work_list);
+	INIT_LIST_HEAD(&worker->delayed_work_list);
+}
+EXPORT_SYMBOL_GPL(__kthread_init_worker);
+
+/**
+ * kthread_worker_fn - kthread function to process kthread_worker
+ * @worker_ptr: pointer to initialized kthread_worker
+ *
+ * This function implements the main cycle of kthread worker. It processes
+ * work_list until it is stopped with kthread_stop(). It sleeps when the queue
+ * is empty.
+ *
+ * The works are not allowed to keep any locks, disable preemption or interrupts
+ * when they finish. There is defined a safe point for freezing when one work
+ * finishes and before a new one is started.
+ *
+ * Also the works must not be handled by more than one worker at the same time,
+ * see also kthread_queue_work().
+ */
+int kthread_worker_fn(void *worker_ptr)
+{
+	struct kthread_worker *worker = worker_ptr;
+	struct kthread_work *work;
+
+	/*
+	 * FIXME: Update the check and remove the assignment when all kthread
+	 * worker users are created using kthread_create_worker*() functions.
+	 */
+	WARN_ON(worker->task && worker->task != current);
+	worker->task = current;
+
+	if (worker->flags & KTW_FREEZABLE)
+		set_freezable();
+
+repeat:
+	set_current_state(TASK_INTERRUPTIBLE);	/* mb paired w/ kthread_stop */
+
+	if (kthread_should_stop()) {
+		__set_current_state(TASK_RUNNING);
+		raw_spin_lock_irq(&worker->lock);
+		worker->task = NULL;
+		raw_spin_unlock_irq(&worker->lock);
+		return 0;
+	}
+
+	work = NULL;
+	raw_spin_lock_irq(&worker->lock);
+	if (!list_empty(&worker->work_list)) {
+		work = list_first_entry(&worker->work_list,
+					struct kthread_work, node);
+		list_del_init(&work->node);
+	}
+	worker->current_work = work;
+	raw_spin_unlock_irq(&worker->lock);
+
+	if (work) {
+		kthread_work_func_t func = work->func;
+		__set_current_state(TASK_RUNNING);
+		trace_sched_kthread_work_execute_start(work);
+		work->func(work);
+		/*
+		 * Avoid dereferencing work after this point.  The trace
+		 * event only cares about the address.
+		 */
+		trace_sched_kthread_work_execute_end(work, func);
+	} else if (!freezing(current))
+		schedule();
+
+	try_to_freeze();
+	cond_resched();
+	goto repeat;
+}
+EXPORT_SYMBOL_GPL(kthread_worker_fn);
+
+static __printf(3, 0) struct kthread_worker *
+__kthread_create_worker(int cpu, unsigned int flags,
+			const char namefmt[], va_list args)
+{
+	struct kthread_worker *worker;
+	struct task_struct *task;
+	int node = NUMA_NO_NODE;
+
+	worker = kzalloc(sizeof(*worker), GFP_KERNEL);
+	if (!worker)
+		return ERR_PTR(-ENOMEM);
+
+	kthread_init_worker(worker);
+
+	if (cpu >= 0)
+		node = cpu_to_node(cpu);
+
+	task = __kthread_create_on_node(kthread_worker_fn, worker,
+						node, namefmt, args);
+	if (IS_ERR(task))
+		goto fail_task;
+
+	if (cpu >= 0)
+		kthread_bind(task, cpu);
+
+	worker->flags = flags;
+	worker->task = task;
+	wake_up_process(task);
+	return worker;
+
+fail_task:
+	kfree(worker);
+	return ERR_CAST(task);
+}
+
+/**
+ * kthread_create_worker - create a kthread worker
+ * @flags: flags modifying the default behavior of the worker
+ * @namefmt: printf-style name for the kthread worker (task).
+ *
+ * Returns a pointer to the allocated worker on success, ERR_PTR(-ENOMEM)
+ * when the needed structures could not get allocated, and ERR_PTR(-EINTR)
+ * when the caller was killed by a fatal signal.
+ */
+struct kthread_worker *
+kthread_create_worker(unsigned int flags, const char namefmt[], ...)
+{
+	struct kthread_worker *worker;
+	va_list args;
+
+	va_start(args, namefmt);
+	worker = __kthread_create_worker(-1, flags, namefmt, args);
+	va_end(args);
+
+	return worker;
+}
+EXPORT_SYMBOL(kthread_create_worker);
+
+/**
+ * kthread_create_worker_on_cpu - create a kthread worker and bind it
+ *	to a given CPU and the associated NUMA node.
+ * @cpu: CPU number
+ * @flags: flags modifying the default behavior of the worker
+ * @namefmt: printf-style name for the kthread worker (task).
+ *
+ * Use a valid CPU number if you want to bind the kthread worker
+ * to the given CPU and the associated NUMA node.
+ *
+ * A good practice is to add the cpu number also into the worker name.
+ * For example, use kthread_create_worker_on_cpu(cpu, "helper/%d", cpu).
+ *
+ * CPU hotplug:
+ * The kthread worker API is simple and generic. It just provides a way
+ * to create, use, and destroy workers.
+ *
+ * It is up to the API user how to handle CPU hotplug. They have to decide
+ * how to handle pending work items, prevent queuing new ones, and
+ * restore the functionality when the CPU goes off and on. There are a
+ * few catches:
+ *
+ *    - CPU affinity gets lost when it is scheduled on an offline CPU.
+ *
+ *    - The worker might not exist when the CPU was off when the user
+ *      created the workers.
+ *
+ * Good practice is to implement two CPU hotplug callbacks and to
+ * destroy/create the worker when the CPU goes down/up.
+ *
+ * Return:
+ * The pointer to the allocated worker on success, ERR_PTR(-ENOMEM)
+ * when the needed structures could not get allocated, and ERR_PTR(-EINTR)
+ * when the caller was killed by a fatal signal.
+ */
+struct kthread_worker *
+kthread_create_worker_on_cpu(int cpu, unsigned int flags,
+			     const char namefmt[], ...)
+{
+	struct kthread_worker *worker;
+	va_list args;
+
+	va_start(args, namefmt);
+	worker = __kthread_create_worker(cpu, flags, namefmt, args);
+	va_end(args);
+
+	return worker;
+}
+EXPORT_SYMBOL(kthread_create_worker_on_cpu);
+
+/*
+ * Returns true when the work could not be queued at the moment.
+ * It happens when it is already pending in a worker list
+ * or when it is being cancelled.
+ */
+static inline bool queuing_blocked(struct kthread_worker *worker,
+				   struct kthread_work *work)
+{
+	lockdep_assert_held(&worker->lock);
+
+	return !list_empty(&work->node) || work->canceling;
+}
+
+static void kthread_insert_work_sanity_check(struct kthread_worker *worker,
+					     struct kthread_work *work)
+{
+	lockdep_assert_held(&worker->lock);
+	WARN_ON_ONCE(!list_empty(&work->node));
+	/* Do not use a work with >1 worker, see kthread_queue_work() */
+	WARN_ON_ONCE(work->worker && work->worker != worker);
+}
+
+/* insert @work before @pos in @worker */
+static void kthread_insert_work(struct kthread_worker *worker,
+				struct kthread_work *work,
+				struct list_head *pos)
+{
+	kthread_insert_work_sanity_check(worker, work);
+
+	trace_sched_kthread_work_queue_work(worker, work);
+
+	list_add_tail(&work->node, pos);
+	work->worker = worker;
+	if (!worker->current_work && likely(worker->task))
+		wake_up_process(worker->task);
+}
+
+/**
+ * kthread_queue_work - queue a kthread_work
+ * @worker: target kthread_worker
+ * @work: kthread_work to queue
+ *
+ * Queue @work to work processor @task for async execution.  @task
+ * must have been created with kthread_worker_create().  Returns %true
+ * if @work was successfully queued, %false if it was already pending.
+ *
+ * Reinitialize the work if it needs to be used by another worker.
+ * For example, when the worker was stopped and started again.
+ */
+bool kthread_queue_work(struct kthread_worker *worker,
+			struct kthread_work *work)
+{
+	bool ret = false;
+	unsigned long flags;
+
+	raw_spin_lock_irqsave(&worker->lock, flags);
+	if (!queuing_blocked(worker, work)) {
+		kthread_insert_work(worker, work, &worker->work_list);
+		ret = true;
+	}
+	raw_spin_unlock_irqrestore(&worker->lock, flags);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(kthread_queue_work);
+
+/**
+ * kthread_delayed_work_timer_fn - callback that queues the associated kthread
+ *	delayed work when the timer expires.
+ * @t: pointer to the expired timer
+ *
+ * The format of the function is defined by struct timer_list.
+ * It should have been called from irqsafe timer with irq already off.
+ */
+void kthread_delayed_work_timer_fn(struct timer_list *t)
+{
+	struct kthread_delayed_work *dwork = from_timer(dwork, t, timer);
+	struct kthread_work *work = &dwork->work;
+	struct kthread_worker *worker = work->worker;
+	unsigned long flags;
+
+	/*
+	 * This might happen when a pending work is reinitialized.
+	 * It means that it is used a wrong way.
+	 */
+	if (WARN_ON_ONCE(!worker))
+		return;
+
+	raw_spin_lock_irqsave(&worker->lock, flags);
+	/* Work must not be used with >1 worker, see kthread_queue_work(). */
+	WARN_ON_ONCE(work->worker != worker);
+
+	/* Move the work from worker->delayed_work_list. */
+	WARN_ON_ONCE(list_empty(&work->node));
+	list_del_init(&work->node);
+	if (!work->canceling)
+		kthread_insert_work(worker, work, &worker->work_list);
+
+	raw_spin_unlock_irqrestore(&worker->lock, flags);
+}
+EXPORT_SYMBOL(kthread_delayed_work_timer_fn);
+
+static void __kthread_queue_delayed_work(struct kthread_worker *worker,
+					 struct kthread_delayed_work *dwork,
+					 unsigned long delay)
+{
+	struct timer_list *timer = &dwork->timer;
+	struct kthread_work *work = &dwork->work;
+
+	WARN_ON_ONCE(timer->function != kthread_delayed_work_timer_fn);
+
+	/*
+	 * If @delay is 0, queue @dwork->work immediately.  This is for
+	 * both optimization and correctness.  The earliest @timer can
+	 * expire is on the closest next tick and delayed_work users depend
+	 * on that there's no such delay when @delay is 0.
+	 */
+	if (!delay) {
+		kthread_insert_work(worker, work, &worker->work_list);
+		return;
+	}
+
+	/* Be paranoid and try to detect possible races already now. */
+	kthread_insert_work_sanity_check(worker, work);
+
+	list_add(&work->node, &worker->delayed_work_list);
+	work->worker = worker;
+	timer->expires = jiffies + delay;
+	add_timer(timer);
+}
+
+/**
+ * kthread_queue_delayed_work - queue the associated kthread work
+ *	after a delay.
+ * @worker: target kthread_worker
+ * @dwork: kthread_delayed_work to queue
+ * @delay: number of jiffies to wait before queuing
+ *
+ * If the work has not been pending it starts a timer that will queue
+ * the work after the given @delay. If @delay is zero, it queues the
+ * work immediately.
+ *
+ * Return: %false if the @work has already been pending. It means that
+ * either the timer was running or the work was queued. It returns %true
+ * otherwise.
+ */
+bool kthread_queue_delayed_work(struct kthread_worker *worker,
+				struct kthread_delayed_work *dwork,
+				unsigned long delay)
+{
+	struct kthread_work *work = &dwork->work;
+	unsigned long flags;
+	bool ret = false;
+
+	raw_spin_lock_irqsave(&worker->lock, flags);
+
+	if (!queuing_blocked(worker, work)) {
+		__kthread_queue_delayed_work(worker, dwork, delay);
+		ret = true;
+	}
+
+	raw_spin_unlock_irqrestore(&worker->lock, flags);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(kthread_queue_delayed_work);
+
+struct kthread_flush_work {
+	struct kthread_work	work;
+	struct completion	done;
+};
+
+static void kthread_flush_work_fn(struct kthread_work *work)
+{
+	struct kthread_flush_work *fwork =
+		container_of(work, struct kthread_flush_work, work);
+	complete(&fwork->done);
+}
+
+/**
+ * kthread_flush_work - flush a kthread_work
+ * @work: work to flush
+ *
+ * If @work is queued or executing, wait for it to finish execution.
+ */
+void kthread_flush_work(struct kthread_work *work)
+{
+	struct kthread_flush_work fwork = {
+		KTHREAD_WORK_INIT(fwork.work, kthread_flush_work_fn),
+		COMPLETION_INITIALIZER_ONSTACK(fwork.done),
+	};
+	struct kthread_worker *worker;
+	bool noop = false;
+
+	worker = work->worker;
+	if (!worker)
+		return;
+
+	raw_spin_lock_irq(&worker->lock);
+	/* Work must not be used with >1 worker, see kthread_queue_work(). */
+	WARN_ON_ONCE(work->worker != worker);
+
+	if (!list_empty(&work->node))
+		kthread_insert_work(worker, &fwork.work, work->node.next);
+	else if (worker->current_work == work)
+		kthread_insert_work(worker, &fwork.work,
+				    worker->work_list.next);
+	else
+		noop = true;
+
+	raw_spin_unlock_irq(&worker->lock);
+
+	if (!noop)
+		wait_for_completion(&fwork.done);
+}
+EXPORT_SYMBOL_GPL(kthread_flush_work);
+
+/*
+ * Make sure that the timer is neither set nor running and could
+ * not manipulate the work list_head any longer.
+ *
+ * The function is called under worker->lock. The lock is temporary
+ * released but the timer can't be set again in the meantime.
+ */
+static void kthread_cancel_delayed_work_timer(struct kthread_work *work,
+					      unsigned long *flags)
+{
+	struct kthread_delayed_work *dwork =
+		container_of(work, struct kthread_delayed_work, work);
+	struct kthread_worker *worker = work->worker;
+
+	/*
+	 * del_timer_sync() must be called to make sure that the timer
+	 * callback is not running. The lock must be temporary released
+	 * to avoid a deadlock with the callback. In the meantime,
+	 * any queuing is blocked by setting the canceling counter.
+	 */
+	work->canceling++;
+	raw_spin_unlock_irqrestore(&worker->lock, *flags);
+	del_timer_sync(&dwork->timer);
+	raw_spin_lock_irqsave(&worker->lock, *flags);
+	work->canceling--;
+}
+
+/*
+ * This function removes the work from the worker queue.
+ *
+ * It is called under worker->lock. The caller must make sure that
+ * the timer used by delayed work is not running, e.g. by calling
+ * kthread_cancel_delayed_work_timer().
+ *
+ * The work might still be in use when this function finishes. See the
+ * current_work proceed by the worker.
+ *
+ * Return: %true if @work was pending and successfully canceled,
+ *	%false if @work was not pending
+ */
+static bool __kthread_cancel_work(struct kthread_work *work)
+{
+	/*
+	 * Try to remove the work from a worker list. It might either
+	 * be from worker->work_list or from worker->delayed_work_list.
+	 */
+	if (!list_empty(&work->node)) {
+		list_del_init(&work->node);
+		return true;
+	}
+
+	return false;
+}
+
+/**
+ * kthread_mod_delayed_work - modify delay of or queue a kthread delayed work
+ * @worker: kthread worker to use
+ * @dwork: kthread delayed work to queue
+ * @delay: number of jiffies to wait before queuing
+ *
+ * If @dwork is idle, equivalent to kthread_queue_delayed_work(). Otherwise,
+ * modify @dwork's timer so that it expires after @delay. If @delay is zero,
+ * @work is guaranteed to be queued immediately.
+ *
+ * Return: %false if @dwork was idle and queued, %true otherwise.
+ *
+ * A special case is when the work is being canceled in parallel.
+ * It might be caused either by the real kthread_cancel_delayed_work_sync()
+ * or yet another kthread_mod_delayed_work() call. We let the other command
+ * win and return %true here. The return value can be used for reference
+ * counting and the number of queued works stays the same. Anyway, the caller
+ * is supposed to synchronize these operations a reasonable way.
+ *
+ * This function is safe to call from any context including IRQ handler.
+ * See __kthread_cancel_work() and kthread_delayed_work_timer_fn()
+ * for details.
+ */
+bool kthread_mod_delayed_work(struct kthread_worker *worker,
+			      struct kthread_delayed_work *dwork,
+			      unsigned long delay)
+{
+	struct kthread_work *work = &dwork->work;
+	unsigned long flags;
+	int ret;
+
+	raw_spin_lock_irqsave(&worker->lock, flags);
+
+	/* Do not bother with canceling when never queued. */
+	if (!work->worker) {
+		ret = false;
+		goto fast_queue;
+	}
+
+	/* Work must not be used with >1 worker, see kthread_queue_work() */
+	WARN_ON_ONCE(work->worker != worker);
+
+	/*
+	 * Temporary cancel the work but do not fight with another command
+	 * that is canceling the work as well.
+	 *
+	 * It is a bit tricky because of possible races with another
+	 * mod_delayed_work() and cancel_delayed_work() callers.
+	 *
+	 * The timer must be canceled first because worker->lock is released
+	 * when doing so. But the work can be removed from the queue (list)
+	 * only when it can be queued again so that the return value can
+	 * be used for reference counting.
+	 */
+	kthread_cancel_delayed_work_timer(work, &flags);
+	if (work->canceling) {
+		/* The number of works in the queue does not change. */
+		ret = true;
+		goto out;
+	}
+	ret = __kthread_cancel_work(work);
+
+fast_queue:
+	__kthread_queue_delayed_work(worker, dwork, delay);
+out:
+	raw_spin_unlock_irqrestore(&worker->lock, flags);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(kthread_mod_delayed_work);
+
+static bool __kthread_cancel_work_sync(struct kthread_work *work, bool is_dwork)
+{
+	struct kthread_worker *worker = work->worker;
+	unsigned long flags;
+	int ret = false;
+
+	if (!worker)
+		goto out;
+
+	raw_spin_lock_irqsave(&worker->lock, flags);
+	/* Work must not be used with >1 worker, see kthread_queue_work(). */
+	WARN_ON_ONCE(work->worker != worker);
+
+	if (is_dwork)
+		kthread_cancel_delayed_work_timer(work, &flags);
+
+	ret = __kthread_cancel_work(work);
+
+	if (worker->current_work != work)
+		goto out_fast;
+
+	/*
+	 * The work is in progress and we need to wait with the lock released.
+	 * In the meantime, block any queuing by setting the canceling counter.
+	 */
+	work->canceling++;
+	raw_spin_unlock_irqrestore(&worker->lock, flags);
+	kthread_flush_work(work);
+	raw_spin_lock_irqsave(&worker->lock, flags);
+	work->canceling--;
+
+out_fast:
+	raw_spin_unlock_irqrestore(&worker->lock, flags);
+out:
+	return ret;
+}
+
+/**
+ * kthread_cancel_work_sync - cancel a kthread work and wait for it to finish
+ * @work: the kthread work to cancel
+ *
+ * Cancel @work and wait for its execution to finish.  This function
+ * can be used even if the work re-queues itself. On return from this
+ * function, @work is guaranteed to be not pending or executing on any CPU.
+ *
+ * kthread_cancel_work_sync(&delayed_work->work) must not be used for
+ * delayed_work's. Use kthread_cancel_delayed_work_sync() instead.
+ *
+ * The caller must ensure that the worker on which @work was last
+ * queued can't be destroyed before this function returns.
+ *
+ * Return: %true if @work was pending, %false otherwise.
+ */
+bool kthread_cancel_work_sync(struct kthread_work *work)
+{
+	return __kthread_cancel_work_sync(work, false);
+}
+EXPORT_SYMBOL_GPL(kthread_cancel_work_sync);
+
+/**
+ * kthread_cancel_delayed_work_sync - cancel a kthread delayed work and
+ *	wait for it to finish.
+ * @dwork: the kthread delayed work to cancel
+ *
+ * This is kthread_cancel_work_sync() for delayed works.
+ *
+ * Return: %true if @dwork was pending, %false otherwise.
+ */
+bool kthread_cancel_delayed_work_sync(struct kthread_delayed_work *dwork)
+{
+	return __kthread_cancel_work_sync(&dwork->work, true);
+}
+EXPORT_SYMBOL_GPL(kthread_cancel_delayed_work_sync);
+
+/**
+ * kthread_flush_worker - flush all current works on a kthread_worker
+ * @worker: worker to flush
+ *
+ * Wait until all currently executing or pending works on @worker are
+ * finished.
+ */
+void kthread_flush_worker(struct kthread_worker *worker)
+{
+	struct kthread_flush_work fwork = {
+		KTHREAD_WORK_INIT(fwork.work, kthread_flush_work_fn),
+		COMPLETION_INITIALIZER_ONSTACK(fwork.done),
+	};
+
+	kthread_queue_work(worker, &fwork.work);
+	wait_for_completion(&fwork.done);
+}
+EXPORT_SYMBOL_GPL(kthread_flush_worker);
+
+/**
+ * kthread_destroy_worker - destroy a kthread worker
+ * @worker: worker to be destroyed
+ *
+ * Flush and destroy @worker.  The simple flush is enough because the kthread
+ * worker API is used only in trivial scenarios.  There are no multi-step state
+ * machines needed.
+ *
+ * Note that this function is not responsible for handling delayed work, so
+ * caller should be responsible for queuing or canceling all delayed work items
+ * before invoke this function.
+ */
+void kthread_destroy_worker(struct kthread_worker *worker)
+{
+	struct task_struct *task;
+
+	task = worker->task;
+	if (WARN_ON(!task))
+		return;
+
+	kthread_flush_worker(worker);
+	kthread_stop(task);
+	WARN_ON(!list_empty(&worker->delayed_work_list));
+	WARN_ON(!list_empty(&worker->work_list));
+	kfree(worker);
+}
+EXPORT_SYMBOL(kthread_destroy_worker);
+
+/**
+ * kthread_use_mm - make the calling kthread operate on an address space
+ * @mm: address space to operate on
+ */
+void kthread_use_mm(struct mm_struct *mm)
+{
+	struct mm_struct *active_mm;
+	struct task_struct *tsk = current;
+
+	WARN_ON_ONCE(!(tsk->flags & PF_KTHREAD));
+	WARN_ON_ONCE(tsk->mm);
+
+	/*
+	 * It is possible for mm to be the same as tsk->active_mm, but
+	 * we must still mmgrab(mm) and mmdrop_lazy_tlb(active_mm),
+	 * because these references are not equivalent.
+	 */
+	mmgrab(mm);
+
+	task_lock(tsk);
+	/* Hold off tlb flush IPIs while switching mm's */
+	local_irq_disable();
+	active_mm = tsk->active_mm;
+	tsk->active_mm = mm;
+	tsk->mm = mm;
+	membarrier_update_current_mm(mm);
+	switch_mm_irqs_off(active_mm, mm, tsk);
+	local_irq_enable();
+	task_unlock(tsk);
+#ifdef finish_arch_post_lock_switch
+	finish_arch_post_lock_switch();
+#endif
+
+	/*
+	 * When a kthread starts operating on an address space, the loop
+	 * in membarrier_{private,global}_expedited() may not observe
+	 * that tsk->mm, and not issue an IPI. Membarrier requires a
+	 * memory barrier after storing to tsk->mm, before accessing
+	 * user-space memory. A full memory barrier for membarrier
+	 * {PRIVATE,GLOBAL}_EXPEDITED is implicitly provided by
+	 * mmdrop_lazy_tlb().
+	 */
+	mmdrop_lazy_tlb(active_mm);
+}
+EXPORT_SYMBOL_GPL(kthread_use_mm);
+
+/**
+ * kthread_unuse_mm - reverse the effect of kthread_use_mm()
+ * @mm: address space to operate on
+ */
+void kthread_unuse_mm(struct mm_struct *mm)
+{
+	struct task_struct *tsk = current;
+
+	WARN_ON_ONCE(!(tsk->flags & PF_KTHREAD));
+	WARN_ON_ONCE(!tsk->mm);
+
+	task_lock(tsk);
+	/*
+	 * When a kthread stops operating on an address space, the loop
+	 * in membarrier_{private,global}_expedited() may not observe
+	 * that tsk->mm, and not issue an IPI. Membarrier requires a
+	 * memory barrier after accessing user-space memory, before
+	 * clearing tsk->mm.
+	 */
+	smp_mb__after_spinlock();
+	sync_mm_rss(mm);
+	local_irq_disable();
+	tsk->mm = NULL;
+	membarrier_update_current_mm(NULL);
+	mmgrab_lazy_tlb(mm);
+	/* active_mm is still 'mm' */
+	enter_lazy_tlb(mm, tsk);
+	local_irq_enable();
+	task_unlock(tsk);
+
+	mmdrop(mm);
+}
+EXPORT_SYMBOL_GPL(kthread_unuse_mm);
+
+#ifdef CONFIG_BLK_CGROUP
+/**
+ * kthread_associate_blkcg - associate blkcg to current kthread
+ * @css: the cgroup info
+ *
+ * Current thread must be a kthread. The thread is running jobs on behalf of
+ * other threads. In some cases, we expect the jobs attach cgroup info of
+ * original threads instead of that of current thread. This function stores
+ * original thread's cgroup info in current kthread context for later
+ * retrieval.
+ */
+void kthread_associate_blkcg(struct cgroup_subsys_state *css)
+{
+	struct kthread *kthread;
+
+	if (!(current->flags & PF_KTHREAD))
+		return;
+	kthread = to_kthread(current);
+	if (!kthread)
+		return;
+
+	if (kthread->blkcg_css) {
+		css_put(kthread->blkcg_css);
+		kthread->blkcg_css = NULL;
+	}
+	if (css) {
+		css_get(css);
+		kthread->blkcg_css = css;
+	}
+}
+EXPORT_SYMBOL(kthread_associate_blkcg);
+
+/**
+ * kthread_blkcg - get associated blkcg css of current kthread
+ *
+ * Current thread must be a kthread.
+ */
+struct cgroup_subsys_state *kthread_blkcg(void)
+{
+	struct kthread *kthread;
+
+	if (current->flags & PF_KTHREAD) {
+		kthread = to_kthread(current);
+		if (kthread)
+			return kthread->blkcg_css;
+	}
+	return NULL;
+}
+#endif