kernel/kthread.c - kernel/msm - Gitiles

 /* Kernel thread helper functions.
  *   Copyright (C) 2004 IBM Corporation, Rusty Russell.
  *
  * 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 <linux/sched.h>
 #include <linux/kthread.h>
 #include <linux/completion.h>
 #include <linux/err.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 <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. */
 	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 {
 	int should_stop;
 	void *data;
 	struct completion exited;
 };

 #define to_kthread(tsk)	\
 	container_of((tsk)->vfork_done, struct kthread, exited)

 /**
  * 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().
  */
 int kthread_should_stop(void)
 {
 	return to_kthread(current)->should_stop;
 }
 EXPORT_SYMBOL(kthread_should_stop);

 /**
  * 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;
 }

 static int kthread(void *_create)
 {
 	/* 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 kthread self;
 	int ret;

 	self.should_stop = 0;
 	self.data = data;
 	init_completion(&self.exited);
 	current->vfork_done = &self.exited;

 	/* OK, tell user we're spawned, wait for stop or wakeup */
 	__set_current_state(TASK_UNINTERRUPTIBLE);
 	create->result = current;
 	complete(&create->done);
 	schedule();

 	ret = -EINTR;
 	if (!self.should_stop)
 		ret = threadfn(data);

 	/* we can't just return, we must preserve "self" on stack */
 	do_exit(ret);
 }

 /* called from do_fork() 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_node_id();
 }

 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, CLONE_FS | CLONE_FILES | SIGCHLD);
 	if (pid < 0) {
 		create->result = ERR_PTR(pid);
 		complete(&create->done);
 	}
 }

 /**
  * kthread_create_on_node - create a kthread.
  * @threadfn: the function to run until signal_pending(current).
  * @data: data ptr for @threadfn.
  * @node: memory node number.
  * @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().
  *
  * 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 -1.
  * When woken, the thread will run @threadfn() with @data as its
  * argument. @threadfn() can either call do_exit() 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).
  */
 struct task_struct *kthread_create_on_node(int (*threadfn)(void *data),
 					   void *data,
 					   int node,
 					   const char namefmt[],
 					   ...)
 {
 	struct kthread_create_info create;

 	create.threadfn = threadfn;
 	create.data = data;
 	create.node = node;
 	init_completion(&create.done);

 	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(&create.done);

 	if (!IS_ERR(create.result)) {
 		static const struct sched_param param = { .sched_priority = 0 };
 		va_list args;

 		va_start(args, namefmt);
 		vsnprintf(create.result->comm, sizeof(create.result->comm),
 			  namefmt, args);
 		va_end(args);
 		/*
 		 * root may have changed our (kthreadd's) priority or CPU mask.
 		 * The kernel thread should not inherit these properties.
 		 */
 		sched_setscheduler_nocheck(create.result, SCHED_NORMAL, &param);
 		set_cpus_allowed_ptr(create.result, cpu_all_mask);
 	}
 	return create.result;
 }
 EXPORT_SYMBOL(kthread_create_on_node);

 /**
  * 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)
 {
 	/* Must have done schedule() in kthread() before we set_task_cpu */
 	if (!wait_task_inactive(p, TASK_UNINTERRUPTIBLE)) {
 		WARN_ON(1);
 		return;
 	}

 	/* It's safe because the task is inactive. */
 	do_set_cpus_allowed(p, cpumask_of(cpu));
 	p->flags |= PF_THREAD_BOUND;
 }
 EXPORT_SYMBOL(kthread_bind);

 /**
  * 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 do_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);
 	barrier(); /* it might have exited */
 	if (k->vfork_done != NULL) {
 		kthread->should_stop = 1;
 		wake_up_process(k);
 		wait_for_completion(&kthread->exited);
 	}
 	ret = k->exit_code;

 	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, cpu_all_mask);
 	set_mems_allowed(node_states[N_HIGH_MEMORY]);

 	current->flags |= PF_NOFREEZE | PF_FREEZER_NOSIG;

 	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 __init_kthread_worker(struct kthread_worker *worker,
 				const char *name,
 				struct lock_class_key *key)
 {
 	spin_lock_init(&worker->lock);
 	lockdep_set_class_and_name(&worker->lock, key, name);
 	INIT_LIST_HEAD(&worker->work_list);
 	worker->task = NULL;
 }
 EXPORT_SYMBOL_GPL(__init_kthread_worker);

 /**
  * kthread_worker_fn - kthread function to process kthread_worker
  * @worker_ptr: pointer to initialized kthread_worker
  *
  * This function can be used as @threadfn to kthread_create() or
  * kthread_run() with @worker_ptr argument pointing to an initialized
  * kthread_worker.  The started kthread will process work_list until
  * the it is stopped with kthread_stop().  A kthread can also call
  * this function directly after extra initialization.
  *
  * Different kthreads can be used for the same kthread_worker as long
  * as there's only one kthread attached to it at any given time.  A
  * kthread_worker without an attached kthread simply collects queued
  * kthread_works.
  */
 int kthread_worker_fn(void *worker_ptr)
 {
 	struct kthread_worker *worker = worker_ptr;
 	struct kthread_work *work;

 	WARN_ON(worker->task);
 	worker->task = current;
 repeat:
 	set_current_state(TASK_INTERRUPTIBLE);	/* mb paired w/ kthread_stop */

 	if (kthread_should_stop()) {
 		__set_current_state(TASK_RUNNING);
 		spin_lock_irq(&worker->lock);
 		worker->task = NULL;
 		spin_unlock_irq(&worker->lock);
 		return 0;
 	}

 	work = NULL;
 	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);
 	}
 	spin_unlock_irq(&worker->lock);

 	if (work) {
 		__set_current_state(TASK_RUNNING);
 		work->func(work);
 		smp_wmb();	/* wmb worker-b0 paired with flush-b1 */
 		work->done_seq = work->queue_seq;
 		smp_mb();	/* mb worker-b1 paired with flush-b0 */
 		if (atomic_read(&work->flushing))
 			wake_up_all(&work->done);
 	} else if (!freezing(current))
 		schedule();

 	try_to_freeze();
 	goto repeat;
 }
 EXPORT_SYMBOL_GPL(kthread_worker_fn);

 /**
  * queue_kthread_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.
  */
 bool queue_kthread_work(struct kthread_worker *worker,
 			struct kthread_work *work)
 {
 	bool ret = false;
 	unsigned long flags;

 	spin_lock_irqsave(&worker->lock, flags);
 	if (list_empty(&work->node)) {
 		list_add_tail(&work->node, &worker->work_list);
 		work->queue_seq++;
 		if (likely(worker->task))
 			wake_up_process(worker->task);
 		ret = true;
 	}
 	spin_unlock_irqrestore(&worker->lock, flags);
 	return ret;
 }
 EXPORT_SYMBOL_GPL(queue_kthread_work);

 /**
  * flush_kthread_work - flush a kthread_work
  * @work: work to flush
  *
  * If @work is queued or executing, wait for it to finish execution.
  */
 void flush_kthread_work(struct kthread_work *work)
 {
 	int seq = work->queue_seq;

 	atomic_inc(&work->flushing);

 	/*
 	 * mb flush-b0 paired with worker-b1, to make sure either
 	 * worker sees the above increment or we see done_seq update.
 	 */
 	smp_mb__after_atomic_inc();

 	/* A - B <= 0 tests whether B is in front of A regardless of overflow */
 	wait_event(work->done, seq - work->done_seq <= 0);
 	atomic_dec(&work->flushing);

 	/*
 	 * rmb flush-b1 paired with worker-b0, to make sure our caller
 	 * sees every change made by work->func().
 	 */
 	smp_mb__after_atomic_dec();
 }
 EXPORT_SYMBOL_GPL(flush_kthread_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);
 }

 /**
  * flush_kthread_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 flush_kthread_worker(struct kthread_worker *worker)
 {
 	struct kthread_flush_work fwork = {
 		KTHREAD_WORK_INIT(fwork.work, kthread_flush_work_fn),
 		COMPLETION_INITIALIZER_ONSTACK(fwork.done),
 	};

 	queue_kthread_work(worker, &fwork.work);
 	wait_for_completion(&fwork.done);
 }
 EXPORT_SYMBOL_GPL(flush_kthread_worker);
	/* Kernel thread helper functions.
	* Copyright (C) 2004 IBM Corporation, Rusty Russell.
	*
	* 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 <linux/sched.h>
	#include <linux/kthread.h>
	#include <linux/completion.h>
	#include <linux/err.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 <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. */
	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 {
	int should_stop;
	void *data;
	struct completion exited;
	};

	#define to_kthread(tsk) \
	container_of((tsk)->vfork_done, struct kthread, exited)

	/**
	* 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().
	*/
	int kthread_should_stop(void)
	{
	return to_kthread(current)->should_stop;
	}
	EXPORT_SYMBOL(kthread_should_stop);

	/**
	* 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;
	}

	static int kthread(void *_create)
	{
	/* 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 kthread self;
	int ret;

	self.should_stop = 0;
	self.data = data;
	init_completion(&self.exited);
	current->vfork_done = &self.exited;

	/* OK, tell user we're spawned, wait for stop or wakeup */
	__set_current_state(TASK_UNINTERRUPTIBLE);
	create->result = current;
	complete(&create->done);
	schedule();

	ret = -EINTR;
	if (!self.should_stop)
	ret = threadfn(data);

	/* we can't just return, we must preserve "self" on stack */
	do_exit(ret);
	}

	/* called from do_fork() 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_node_id();
	}

	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, CLONE_FS \| CLONE_FILES \| SIGCHLD);
	if (pid < 0) {
	create->result = ERR_PTR(pid);
	complete(&create->done);
	}
	}

	/**
	* kthread_create_on_node - create a kthread.
	* @threadfn: the function to run until signal_pending(current).
	* @data: data ptr for @threadfn.
	* @node: memory node number.
	* @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().
	*
	* 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 -1.
	* When woken, the thread will run @threadfn() with @data as its
	* argument. @threadfn() can either call do_exit() 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).
	*/
	struct task_struct kthread_create_on_node(int (threadfn)(void *data),
	void *data,
	int node,
	const char namefmt[],
	...)
	{
	struct kthread_create_info create;

	create.threadfn = threadfn;
	create.data = data;
	create.node = node;
	init_completion(&create.done);

	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(&create.done);

	if (!IS_ERR(create.result)) {
	static const struct sched_param param = { .sched_priority = 0 };
	va_list args;

	va_start(args, namefmt);
	vsnprintf(create.result->comm, sizeof(create.result->comm),
	namefmt, args);
	va_end(args);
	/*
	* root may have changed our (kthreadd's) priority or CPU mask.
	* The kernel thread should not inherit these properties.
	*/
	sched_setscheduler_nocheck(create.result, SCHED_NORMAL, &param);
	set_cpus_allowed_ptr(create.result, cpu_all_mask);
	}
	return create.result;
	}
	EXPORT_SYMBOL(kthread_create_on_node);

	/**
	* 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)
	{
	/* Must have done schedule() in kthread() before we set_task_cpu */
	if (!wait_task_inactive(p, TASK_UNINTERRUPTIBLE)) {
	WARN_ON(1);
	return;
	}

	/* It's safe because the task is inactive. */
	do_set_cpus_allowed(p, cpumask_of(cpu));
	p->flags \|= PF_THREAD_BOUND;
	}
	EXPORT_SYMBOL(kthread_bind);

	/**
	* 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 do_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);
	barrier(); /* it might have exited */
	if (k->vfork_done != NULL) {
	kthread->should_stop = 1;
	wake_up_process(k);
	wait_for_completion(&kthread->exited);
	}
	ret = k->exit_code;

	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, cpu_all_mask);
	set_mems_allowed(node_states[N_HIGH_MEMORY]);

	current->flags \|= PF_NOFREEZE \| PF_FREEZER_NOSIG;

	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 __init_kthread_worker(struct kthread_worker *worker,
	const char *name,
	struct lock_class_key *key)
	{
	spin_lock_init(&worker->lock);
	lockdep_set_class_and_name(&worker->lock, key, name);
	INIT_LIST_HEAD(&worker->work_list);
	worker->task = NULL;
	}
	EXPORT_SYMBOL_GPL(__init_kthread_worker);

	/**
	* kthread_worker_fn - kthread function to process kthread_worker
	* @worker_ptr: pointer to initialized kthread_worker
	*
	* This function can be used as @threadfn to kthread_create() or
	* kthread_run() with @worker_ptr argument pointing to an initialized
	* kthread_worker. The started kthread will process work_list until
	* the it is stopped with kthread_stop(). A kthread can also call
	* this function directly after extra initialization.
	*
	* Different kthreads can be used for the same kthread_worker as long
	* as there's only one kthread attached to it at any given time. A
	* kthread_worker without an attached kthread simply collects queued
	* kthread_works.
	*/
	int kthread_worker_fn(void *worker_ptr)
	{
	struct kthread_worker *worker = worker_ptr;
	struct kthread_work *work;

	WARN_ON(worker->task);
	worker->task = current;
	repeat:
	set_current_state(TASK_INTERRUPTIBLE); /* mb paired w/ kthread_stop */

	if (kthread_should_stop()) {
	__set_current_state(TASK_RUNNING);
	spin_lock_irq(&worker->lock);
	worker->task = NULL;
	spin_unlock_irq(&worker->lock);
	return 0;
	}

	work = NULL;
	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);
	}
	spin_unlock_irq(&worker->lock);

	if (work) {
	__set_current_state(TASK_RUNNING);
	work->func(work);
	smp_wmb(); /* wmb worker-b0 paired with flush-b1 */
	work->done_seq = work->queue_seq;
	smp_mb(); /* mb worker-b1 paired with flush-b0 */
	if (atomic_read(&work->flushing))
	wake_up_all(&work->done);
	} else if (!freezing(current))
	schedule();

	try_to_freeze();
	goto repeat;
	}
	EXPORT_SYMBOL_GPL(kthread_worker_fn);

	/**
	* queue_kthread_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.
	*/
	bool queue_kthread_work(struct kthread_worker *worker,
	struct kthread_work *work)
	{
	bool ret = false;
	unsigned long flags;

	spin_lock_irqsave(&worker->lock, flags);
	if (list_empty(&work->node)) {
	list_add_tail(&work->node, &worker->work_list);
	work->queue_seq++;
	if (likely(worker->task))
	wake_up_process(worker->task);
	ret = true;
	}
	spin_unlock_irqrestore(&worker->lock, flags);
	return ret;
	}
	EXPORT_SYMBOL_GPL(queue_kthread_work);

	/**
	* flush_kthread_work - flush a kthread_work
	* @work: work to flush
	*
	* If @work is queued or executing, wait for it to finish execution.
	*/
	void flush_kthread_work(struct kthread_work *work)
	{
	int seq = work->queue_seq;

	atomic_inc(&work->flushing);

	/*
	* mb flush-b0 paired with worker-b1, to make sure either
	* worker sees the above increment or we see done_seq update.
	*/
	smp_mb__after_atomic_inc();

	/* A - B <= 0 tests whether B is in front of A regardless of overflow */
	wait_event(work->done, seq - work->done_seq <= 0);
	atomic_dec(&work->flushing);

	/*
	* rmb flush-b1 paired with worker-b0, to make sure our caller
	* sees every change made by work->func().
	*/
	smp_mb__after_atomic_dec();
	}
	EXPORT_SYMBOL_GPL(flush_kthread_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);
	}

	/**
	* flush_kthread_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 flush_kthread_worker(struct kthread_worker *worker)
	{
	struct kthread_flush_work fwork = {
	KTHREAD_WORK_INIT(fwork.work, kthread_flush_work_fn),
	COMPLETION_INITIALIZER_ONSTACK(fwork.done),
	};

	queue_kthread_work(worker, &fwork.work);
	wait_for_completion(&fwork.done);
	}
	EXPORT_SYMBOL_GPL(flush_kthread_worker);