linux-kernel - [PATCH] workqueue: fix locking in retry path of maybe_create

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Date:	Mon, 12 Jul 2010 10:53:18 +0200
From:	Tejun Heo <tj@...nel.org>
To:	Yong Zhang <yong.zhang@...driver.com>
CC:	torvalds@...ux-foundation.org, mingo@...e.hu,
	linux-kernel@...r.kernel.org, jeff@...zik.org,
	akpm@...ux-foundation.org, rusty@...tcorp.com.au,
	cl@...ux-foundation.org, dhowells@...hat.com,
	arjan@...ux.intel.com, oleg@...hat.com, axboe@...nel.dk,
	fweisbec@...il.com, dwalker@...eaurora.org,
	stefanr@...6.in-berlin.de, florian@...kler.org,
	andi@...stfloor.org, mst@...hat.com, randy.dunlap@...cle.com
Subject: [PATCH] workqueue: fix locking in retry path of maybe_create_worker()

maybe_create_worker() mismanaged locking when worker creation fails
and it has to retry.  Fix locking and simplify lock manipulation.

Signed-off-by: Tejun Heo <tj@...nel.org>
Reported-by: Yong Zhang <yong.zhang@...driver.com>
---
Heh, that was stupid.  Thanks a lot for spotting it.  I simplified
things a bit there as there's no reason to repeatedly lock and unlock
there.  Does this look good to you?

 kernel/workqueue.c |    8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

Index: work/kernel/workqueue.c
===================================================================
--- work.orig/kernel/workqueue.c
+++ work/kernel/workqueue.c
@@ -1442,14 +1442,14 @@ static bool maybe_create_worker(struct g
 	if (!need_to_create_worker(gcwq))
 		return false;
 restart:
+	spin_unlock_irq(&gcwq->lock);
+
 	/* if we don't make progress in MAYDAY_INITIAL_TIMEOUT, call for help */
 	mod_timer(&gcwq->mayday_timer, jiffies + MAYDAY_INITIAL_TIMEOUT);

 	while (true) {
 		struct worker *worker;

-		spin_unlock_irq(&gcwq->lock);
-
 		worker = create_worker(gcwq, true);
 		if (worker) {
 			del_timer_sync(&gcwq->mayday_timer);
@@ -1462,15 +1462,13 @@ restart:
 		if (!need_to_create_worker(gcwq))
 			break;

-		spin_unlock_irq(&gcwq->lock);
 		__set_current_state(TASK_INTERRUPTIBLE);
 		schedule_timeout(CREATE_COOLDOWN);
-		spin_lock_irq(&gcwq->lock);
+
 		if (!need_to_create_worker(gcwq))
 			break;
 	}

-	spin_unlock_irq(&gcwq->lock);
 	del_timer_sync(&gcwq->mayday_timer);
 	spin_lock_irq(&gcwq->lock);
 	if (need_to_create_worker(gcwq))
--
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