Commit fa2563e4 authored Sep 14, 2011 by Thomas Tuttle Committed by Linus Torvalds Sep 14, 2011

workqueue: lock cwq access in drain_workqueue



Take cwq->gcwq->lock to avoid racing between drain_workqueue checking to
make sure the workqueues are empty and cwq_dec_nr_in_flight decrementing
and then incrementing nr_active when it activates a delayed work.

We discovered this when a corner case in one of our drivers resulted in
us trying to destroy a workqueue in which the remaining work would
always requeue itself again in the same workqueue.  We would hit this
race condition and trip the BUG_ON on workqueue.c:3080.

Signed-off-by: Thomas Tuttle <ttuttle@chromium.org>
Acked-by: Tejun Heo <tj@kernel.org>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent df4e33ad

kernel/workqueue.c

+6 −1

Original line number	Diff line number	Diff line
		@@ -2412,8 +2412,13 @@ reflush:

		for_each_cwq_cpu(cpu, wq) {
		struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);
		bool drained;

		if (!cwq->nr_active && list_empty(&cwq->delayed_works))
		spin_lock_irq(&cwq->gcwq->lock);
		drained = !cwq->nr_active && list_empty(&cwq->delayed_works);
		spin_unlock_irq(&cwq->gcwq->lock);

		if (drained)
		continue;

		if (++flush_cnt == 10 \|\|