linux-kernel - [PATCH -mm] workqueue: debug possible endless loop in cancel_rearming_delayed

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Message-ID: <20070420110954.GA3640@ff.dom.local>
Date:	Fri, 20 Apr 2007 13:09:54 +0200
From:	Jarek Poplawski <jarkao2@...pl>
To:	linux-kernel@...r.kernel.org
Cc:	Ingo Molnar <mingo@...e.hu>, Oleg Nesterov <oleg@...sign.ru>
Subject: [PATCH -mm] workqueue: debug possible endless loop in cancel_rearming_delayed_work

(take 2)

I'm not sure we've agreed enough, who'll resubmit, so here
it is with WARN_ON. If it was submited already - forget it.

Jarek P.

--->
IMHO cancel_rearming_delayed_work is dangerous place:

- it assumes a work function always rearms (with no exception),
which probably isn't explained enough now (but anyway should
be checked in such loops);

- probably possible (theoretical) scenario: a few work
functions rearm themselves with very short, equal times;
before flush_workqueue ends, their timers are already
fired, so cancel_delayed_work has nothing to do.

Maybe this patch could check, if I'm not dreaming...

PS: of course the counter value below is a question of taste

Signed-off-by: Jarek Poplawski <jarkao2@...pl>

---

diff -Nurp 2.6.21-rc6-mm1-/kernel/workqueue.c 2.6.21-rc6-mm1/kernel/workqueue.c
--- 2.6.21-rc6-mm1-/kernel/workqueue.c	2007-04-18 20:07:45.000000000 +0200
+++ 2.6.21-rc6-mm1/kernel/workqueue.c	2007-04-18 20:15:44.000000000 +0200
@@ -557,9 +557,12 @@ void cancel_rearming_delayed_work(struct
 	/* Was it ever queued ? */
 	if (cwq != NULL) {
 		struct workqueue_struct *wq = cwq->wq;
+		int i = 1000;
 
-		while (!cancel_delayed_work(dwork))
+		while (!cancel_delayed_work(dwork)) {
 			flush_workqueue(wq);
+			WARN_ON(!i--);
+		}
 	}
 }
 EXPORT_SYMBOL(cancel_rearming_delayed_work);

-
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