linux-kernel - [PATCH] worker_thread: fix racy try_to

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Message-ID: <20070408182047.GA317@tv-sign.ru>
Date:	Sun, 8 Apr 2007 22:20:47 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Srivatsa Vaddagiri <vatsa@...ibm.com>,
	Gautham R Shenoy <ego@...ibm.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>, linux-kernel@...r.kernel.org
Subject: [PATCH] worker_thread: fix racy try_to_freeze() usage

worker_thread() can miss freeze_process()->signal_wake_up() if it happens
between try_to_freeze() and prepare_to_wait(). We should check freezing()
before entering schedule().

This race was introduced by me in

	[PATCH 1/1] workqueue: don't migrate pending works from the dead CPU

Looks like mm/vmscan.c:kswapd() has the same race.

Signed-off-by: Oleg Nesterov <oleg@...sign.ru>

--- 2.6.21-rc5-mm4/kernel/workqueue.c~wq_freeze	2007-04-07 20:11:14.000000000 +0400
+++ 2.6.21-rc5-mm4/kernel/workqueue.c	2007-04-08 21:37:43.000000000 +0400
@@ -307,14 +307,14 @@ static int worker_thread(void *__cwq)
 	do_sigaction(SIGCHLD, &sa, (struct k_sigaction *)0);
 
 	for (;;) {
-		if (cwq->wq->freezeable)
-			try_to_freeze();
-
 		prepare_to_wait(&cwq->more_work, &wait, TASK_INTERRUPTIBLE);
-		if (!cwq->should_stop && list_empty(&cwq->worklist))
+		if (!freezing(current) && !cwq->should_stop
+		    && list_empty(&cwq->worklist))
 			schedule();
 		finish_wait(&cwq->more_work, &wait);
 
+		try_to_freeze();
+
 		if (cwq_should_stop(cwq))
 			break;
 

-
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