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workqueue: separate out drain_workqueue() from destroy_workqueue()

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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: Tejun Heo <tj@kernel.org>
Cc: James Bottomley <James.Bottomley@hansenpartnership.com>
This commit is contained in:
Tejun Heo 2011-04-05 18:01:44 +02:00
parent 2543a87108
commit 9c5a2ba702
2 changed files with 55 additions and 29 deletions
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3
include/linux/workqueue.h
View File

@ -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);

81
kernel/workqueue.c
View File

@ -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