tree 7d0dbcc4214a3bceb4d1dd9251df88752c1313b5
parent df4e33ad249b7480d6ba5dd11fc1dac5cfaffce1
author Thomas Tuttle <ttuttle@chromium.org> 1316042548 -0700
committer Linus Torvalds <torvalds@linux-foundation.org> 1316048978 -0700

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>