linux-kernel - Re: [PATCH] destroy_workqueue() can livelock

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Message-ID: <4697B056.9080508@redhat.com>
Date:	Fri, 13 Jul 2007 19:03:18 +0200
From:	Michal Schmidt <mschmidt@...hat.com>
To:	Oleg Nesterov <oleg@...sign.ru>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Srivatsa Vaddagiri <vatsa@...ibm.com>, stable@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] destroy_workqueue() can livelock

Oleg Nesterov wrote:
> Pointed out by Michal Schmidt <mschmidt@...hat.com>.
> 
> The bug was introduced in 2.6.22 by me.
> 
> cleanup_workqueue_thread() does flush_cpu_workqueue(cwq) in a loop until
> ->worklist becomes empty. This is live-lockable, a re-niced caller can
> get CPU after wake_up() and insert a new barrier before the lower-priority
> cwq->thread has a chance to clear ->current_work.
> 
> Change cleanup_workqueue_thread() to do flush_cpu_workqueue(cwq) only once.
> We can rely on the fact that run_workqueue() won't return until it flushes
> all works. So it is safe to call kthread_stop() after that, the "should stop"
> request won't be noticed until run_workqueue() returns.
> 
> Signed-off-by: Oleg Nesterov <oleg@...sign.ru>

I confirm the patch fixes the bug I was seeing.

Michal

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