linux-kernel - Re: [PATCH v3] workqueue: lock cwq access in drain

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Message-ID: <20110911034851.GA6428@mtj.dyndns.org>
Date:	Sun, 11 Sep 2011 12:48:51 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Thomas Tuttle <ttuttle@...omium.org>
Cc:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	stable@...nel.org
Subject: Re: [PATCH v3] workqueue: lock cwq access in drain_workqueue

On Sat, Sep 10, 2011 at 11:39:53PM -0400, Thomas Tuttle wrote:
> Take cwq->gcwq->lock to avoid racing between drain_workqueue checking
> to make sure the workqueues are empty and cwq_dec_nr_in_flight
> decrementing and then incrementing nr_active when it activates a
> delayed work.
> 
> We discovered this when a corner case in one of our drivers resulted in
> us trying to destroy a workqueue in which the remaining work would
> always requeue itself again in the same workqueue.  We would hit this
> race condition and trip the BUG_ON on workqueue.c:3080.
> 
> Signed-off-by: Thomas Tuttle <ttuttle@...omium.org>
> Acked-by: Tejun Heo <tj@...nel.org>
> Cc: stable@...nel.org

Andrew, can you please route this patch through -mm?  korg is still
down and wq is unlikely to receive many more patches in this cycle.

Thank you.

-- 
tejun
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