linux-kernel - [PATCH] workqueue: fix leak of active

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Message-ID: <50568D85.5030309@cn.fujitsu.com>
Date:	Mon, 17 Sep 2012 10:40:05 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	Tejun Heo <tj@...nel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH] workqueue: fix leak of active

try_to_grab_pending() leave LINKED tagalong in delayed queue when
it deletes a work. This behavior will cause future
cwq_activate_first_delayed() increase the ->nr_active wrongly,
and may cause the whole cwq frozen.

example:

state:	cwq->max_active = 1, cwq->nr_active = 1
	one work in cwq->pool, many in cwq->delayed_works.

step1:	try_to_grab_pending() remove a work from delayed_works but leave tagalong.
step2:	when the work in cwq->pool is finished, cwq_activate_first_delayed()
	move the tagalong to cwq->pool and increase the ->nr_active.

current state: cwq->nr_active = 1, but works of the cwq in cwq->pool are all NO_COLOR,
	so even when these works are finished, cwq->nr_active will not be decreased,
	and no work will be moved from cwq->delayed_works. the cwq is frozen.

Fix it by moving the tagalong to cwq->pool in try_to_grab_pending().

Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
---
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 7b91332..1a268b2 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1101,11 +1101,26 @@ static int try_to_grab_pending(struct work_struct *work, bool is_dwork,
 		 */
 		smp_rmb();
 		if (gcwq == get_work_gcwq(work)) {
+			unsigned long delayed;
+
+			/*
+			 * move LINKED tagalong(if exist) out from
+			 * delayed queue. Otherwise some future
+			 * cwq_activate_first_delayed() may move
+			 * works(which are all NO_COLOR) to cwq->pool
+			 * and increase the ->nr_active. It may
+			 * cause the whole cwq frozen.
+			 */
+			delayed = *work_data_bits(work) & WORK_STRUCT_DELAYED;
+			if (delayed)
+				move_linked_works(work,
+					&get_work_cwq(work)->pool->worklist,
+					NULL);
+
 			debug_work_deactivate(work);
 			list_del_init(&work->entry);
 			cwq_dec_nr_in_flight(get_work_cwq(work),
-				get_work_color(work),
-				*work_data_bits(work) & WORK_STRUCT_DELAYED);
+				get_work_color(work), delayed);
 
 			spin_unlock(&gcwq->lock);
 			return 1;
--
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