Commit 9c5a2ba7 authored by Tejun Heo's avatar Tejun Heo
Browse files

workqueue: separate out drain_workqueue() from destroy_workqueue() 



There are users which want to drain workqueues without destroying it.
Separate out drain functionality from destroy_workqueue() into
drain_workqueue() and make it accessible to workqueue users.

To guarantee forward-progress, only chain queueing is allowed while
drain is in progress.  If a new work item which isn't chained from the
running or pending work items is queued while draining is in progress,
WARN_ON_ONCE() is triggered.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Cc: James Bottomley <James.Bottomley@hansenpartnership.com>
parent 2543a871

include/linux/workqueue.h

+2 −1
Original line number Diff line number Diff line
@@ -255,7 +255,7 @@ enum { 
	WQ_HIGHPRI		= 1 << 4, /* high priority */

	WQ_CPU_INTENSIVE	= 1 << 5, /* cpu instensive workqueue */



	WQ_DYING		= 1 << 6, /* internal: workqueue is dying */

	WQ_DRAINING		= 1 << 6, /* internal: workqueue is draining */

	WQ_RESCUER		= 1 << 7, /* internal: workqueue has rescuer */



	WQ_MAX_ACTIVE		= 512,	  /* I like 512, better ideas? */
@@ -355,6 +355,7 @@ extern int queue_delayed_work_on(int cpu, struct workqueue_struct *wq, 
			struct delayed_work *work, unsigned long delay);



extern void flush_workqueue(struct workqueue_struct *wq);

extern void drain_workqueue(struct workqueue_struct *wq);

extern void flush_scheduled_work(void);



extern int schedule_work(struct work_struct *work);

kernel/workqueue.c

+53 −28
Original line number Diff line number Diff line
@@ -221,7 +221,7 @@ typedef unsigned long mayday_mask_t; 
 * per-CPU workqueues:

 */

struct workqueue_struct {

	unsigned int		flags;		/* I: WQ_* flags */

	unsigned int		flags;		/* W: WQ_* flags */

	union {

		struct cpu_workqueue_struct __percpu	*pcpu;

		struct cpu_workqueue_struct		*single;
@@ -240,6 +240,7 @@ struct workqueue_struct { 
	mayday_mask_t		mayday_mask;	/* cpus requesting rescue */

	struct worker		*rescuer;	/* I: rescue worker */



	int			nr_drainers;	/* W: drain in progress */

	int			saved_max_active; /* W: saved cwq max_active */

	const char		*name;		/* I: workqueue name */

#ifdef CONFIG_LOCKDEP
@@ -990,7 +991,7 @@ static void __queue_work(unsigned int cpu, struct workqueue_struct *wq, 
	debug_work_activate(work);



	/* if dying, only works from the same workqueue are allowed */

	if (unlikely(wq->flags & WQ_DYING) &&

	if (unlikely(wq->flags & WQ_DRAINING) &&

	    WARN_ON_ONCE(!is_chained_work(wq)))

		return;
@@ -2381,6 +2382,54 @@ out_unlock: 
}

EXPORT_SYMBOL_GPL(flush_workqueue);



/**

 * drain_workqueue - drain a workqueue

 * @wq: workqueue to drain

 *

 * Wait until the workqueue becomes empty.  While draining is in progress,

 * only chain queueing is allowed.  IOW, only currently pending or running

 * work items on @wq can queue further work items on it.  @wq is flushed

 * repeatedly until it becomes empty.  The number of flushing is detemined

 * by the depth of chaining and should be relatively short.  Whine if it

 * takes too long.

 */

void drain_workqueue(struct workqueue_struct *wq)

{

	unsigned int flush_cnt = 0;

	unsigned int cpu;



	/*

	 * __queue_work() needs to test whether there are drainers, is much

	 * hotter than drain_workqueue() and already looks at @wq->flags.

	 * Use WQ_DRAINING so that queue doesn't have to check nr_drainers.

	 */

	spin_lock(&workqueue_lock);

	if (!wq->nr_drainers++)

		wq->flags |= WQ_DRAINING;

	spin_unlock(&workqueue_lock);

reflush:

	flush_workqueue(wq);



	for_each_cwq_cpu(cpu, wq) {

		struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);



		if (!cwq->nr_active && list_empty(&cwq->delayed_works))

			continue;



		if (++flush_cnt == 10 ||

		    (flush_cnt % 100 == 0 && flush_cnt <= 1000))

			pr_warning("workqueue %s: flush on destruction isn't complete after %u tries\n",

				   wq->name, flush_cnt);

		goto reflush;

	}



	spin_lock(&workqueue_lock);

	if (!--wq->nr_drainers)

		wq->flags &= ~WQ_DRAINING;

	spin_unlock(&workqueue_lock);

}

EXPORT_SYMBOL_GPL(drain_workqueue);



static bool start_flush_work(struct work_struct *work, struct wq_barrier *barr,

			     bool wait_executing)

{
@@ -3011,34 +3060,10 @@ EXPORT_SYMBOL_GPL(__alloc_workqueue_key); 
 */

void destroy_workqueue(struct workqueue_struct *wq)

{

	unsigned int flush_cnt = 0;

	unsigned int cpu;



	/*

	 * Mark @wq dying and drain all pending works.  Once WQ_DYING is

	 * set, only chain queueing is allowed.  IOW, only currently

	 * pending or running work items on @wq can queue further work

	 * items on it.  @wq is flushed repeatedly until it becomes empty.

	 * The number of flushing is detemined by the depth of chaining and

	 * should be relatively short.  Whine if it takes too long.

	 */

	wq->flags |= WQ_DYING;

reflush:

	flush_workqueue(wq);



	for_each_cwq_cpu(cpu, wq) {

		struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);



		if (!cwq->nr_active && list_empty(&cwq->delayed_works))

			continue;



		if (++flush_cnt == 10 ||

		    (flush_cnt % 100 == 0 && flush_cnt <= 1000))

			printk(KERN_WARNING "workqueue %s: flush on "

			       "destruction isn't complete after %u tries\n",

			       wq->name, flush_cnt);

		goto reflush;

	}

	/* drain it before proceeding with destruction */

	drain_workqueue(wq);



	/*

	 * wq list is used to freeze wq, remove from list after

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