Commit 77668c8b authored Apr 18, 2014 by Lai Jiangshan Committed by Tejun Heo Apr 18, 2014

workqueue: fix a possible race condition between rescuer and pwq-release



There is a race condition between rescuer_thread() and
pwq_unbound_release_workfn().

Even after a pwq is scheduled for rescue, the associated work items
may be consumed by any worker.  If all of them are consumed before the
rescuer gets to them and the pwq's base ref was put due to attribute
change, the pwq may be released while still being linked on
@wq->maydays list making the rescuer dereference already freed pwq
later.

Make send_mayday() pin the target pwq until the rescuer is done with
it.

tj: Updated comment and patch description.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: stable@vger.kernel.org # v3.10+

parent 4d595b86

kernel/workqueue.c

+12 −0

Original line number	Diff line number	Diff line
		@@ -1916,6 +1916,12 @@ static void send_mayday(struct work_struct *work)

		/* mayday mayday mayday */
		if (list_empty(&pwq->mayday_node)) {
		/*
		* If @pwq is for an unbound wq, its base ref may be put at
		* any time due to an attribute change. Pin @pwq until the
		* rescuer is done with it.
		*/
		get_pwq(pwq);
		list_add_tail(&pwq->mayday_node, &wq->maydays);
		wake_up_process(wq->rescuer->task);
		}
		@@ -2449,6 +2455,12 @@ static int rescuer_thread(void *__rescuer)

		process_scheduled_works(rescuer);

		/*
		* Put the reference grabbed by send_mayday(). @pool won't
		* go away while we're holding its lock.
		*/
		put_pwq(pwq);

		/*
		* Leave this pool. If keep_working() is %true, notify a
		* regular worker; otherwise, we end up with 0 concurrency