From: Thomas Tuttle Date: Wed, 14 Sep 2011 23:22:28 +0000 (-0700) Subject: workqueue: lock cwq access in drain_workqueue X-Git-Tag: firefly_0821_release~7541^2~2744 X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=d5b1a08d0d0a73c716766275eb0c5648e143ca85;p=firefly-linux-kernel-4.4.55.git workqueue: lock cwq access in drain_workqueue commit fa2563e41c3d6d6e8af437643981ed28ae0cb56d upstream. 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 Acked-by: Tejun Heo Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- diff --git a/kernel/workqueue.c b/kernel/workqueue.c index 0400553f0d04..aec02b6a1c4a 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -3026,8 +3026,13 @@ 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 ||