Commit 544ecf31 authored May 14, 2012 by Tejun Heo

workqueue: skip nr_running sanity check in worker_enter_idle() if trustee is active



worker_enter_idle() has WARN_ON_ONCE() which triggers if nr_running
isn't zero when every worker is idle.  This can trigger spuriously
while a cpu is going down due to the way trustee sets %WORKER_ROGUE
and zaps nr_running.

It first sets %WORKER_ROGUE on all workers without updating
nr_running, releases gcwq->lock, schedules, regrabs gcwq->lock and
then zaps nr_running.  If the last running worker enters idle
inbetween, it would see stale nr_running which hasn't been zapped yet
and trigger the WARN_ON_ONCE().

Fix it by performing the sanity check iff the trustee is idle.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: stable@vger.kernel.org

parent 0976dfc1

kernel/workqueue.c

+7 −2

Original line number	Diff line number	Diff line
		@@ -1213,8 +1213,13 @@ static void worker_enter_idle(struct worker *worker)
		} else
		wake_up_all(&gcwq->trustee_wait);

		/* sanity check nr_running */
		WARN_ON_ONCE(gcwq->nr_workers == gcwq->nr_idle &&
		/*
		* Sanity check nr_running. Because trustee releases gcwq->lock
		* between setting %WORKER_ROGUE and zapping nr_running, the
		* warning may trigger spuriously. Check iff trustee is idle.
		*/
		WARN_ON_ONCE(gcwq->trustee_state == TRUSTEE_DONE &&
		gcwq->nr_workers == gcwq->nr_idle &&
		atomic_read(get_gcwq_nr_running(gcwq->cpu)));
		}