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workqueue: Don't rely on wq->rescuer to stop rescuer 

The commit1 def98c84b6 ("workqueue: Fix spurious sanity check failures
in destroy_workqueue()") tries to fix spurious sanity check failures by
stopping send_mayday() via setting wq->rescuer to NULL.

But it fails to stop the pwq->mayday_node requeuing in the rescuer, and
the commit2 e66b39af00 ("workqueue: Fix pwq ref leak in
rescuer_thread()") fixes it by checking wq->rescuer which is the result
of commit1.

Both commits together really fix spurious sanity check failures caused
by the rescuer, but they both use a convoluted method by relying on
wq->rescuer state rather than the real count of work items.

Actually __WQ_DESTROYING and drain_workqueue() together already stop
send_mayday() by draining all the work items and ensuring no new work
item requeuing.

And the more proper fix to stop the pwq->mayday_node requeuing in the
rescuer is from commit3 4f3f4cf388 ("workqueue: avoid unneeded
requeuing the pwq in rescuer thread") and renders the checking of
wq->rescuer in commit2 unnecessary.

So __WQ_DESTROYING, drain_workqueue() and commit3 together fix spurious
sanity check failures introduced by the rescuer.

Just remove the convoluted code of using wq->rescuer.

Signed-off-by: Lai Jiangshan <jiangshan.ljs@antgroup.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Lai Jiangshan 2025-11-21 22:57:16 +08:00 committed by Tejun Heo
parent 7b05c90b33
commit 6d90215dc0
1 changed files with 5 additions and 12 deletions
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17
kernel/workqueue.c
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@ -3539,10 +3539,9 @@ static int rescuer_thread(void *__rescuer)
if (pwq->nr_active && need_to_create_worker(pool)) { if (pwq->nr_active && need_to_create_worker(pool)) {
raw_spin_lock(&wq_mayday_lock); raw_spin_lock(&wq_mayday_lock);
/* /*
* Queue iff we aren't racing destruction * Queue iff somebody else hasn't queued it already.
* and somebody else hasn't queued it already.
*/ */
if (wq->rescuer && list_empty(&pwq->mayday_node)) { if (list_empty(&pwq->mayday_node)) {
get_pwq(pwq); get_pwq(pwq);
list_add_tail(&pwq->mayday_node, &wq->maydays); list_add_tail(&pwq->mayday_node, &wq->maydays);
} }
@ -5905,16 +5904,10 @@ void destroy_workqueue(struct workqueue_struct *wq)
/* kill rescuer, if sanity checks fail, leave it w/o rescuer */ /* kill rescuer, if sanity checks fail, leave it w/o rescuer */
if (wq->rescuer) { if (wq->rescuer) {
struct worker *rescuer = wq->rescuer;
/* this prevents new queueing */
raw_spin_lock_irq(&wq_mayday_lock);
wq->rescuer = NULL;
raw_spin_unlock_irq(&wq_mayday_lock);
/* rescuer will empty maydays list before exiting */ /* rescuer will empty maydays list before exiting */
kthread_stop(rescuer->task); kthread_stop(wq->rescuer->task);
kfree(rescuer); kfree(wq->rescuer);
wq->rescuer = NULL;
} }
/* /*