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From: Yong Zhang <yong.zhang0@gmail.com>
To: Stephen Boyd <sboyd@codeaurora.org>
Cc: linux-kernel@vger.kernel.org, Tejun Heo <tj@kernel.org>,
	netdev@vger.kernel.org, Ben Dooks <ben-linux@fluff.org>
Subject: Re: [PATCH 1/2] workqueue: Catch more locking problems with flush_work()
Date: Fri, 20 Apr 2012 15:18:00 +0800	[thread overview]
Message-ID: <20120420071759.GA17846@zhy> (raw)
In-Reply-To: <4F9101A7.5010100@codeaurora.org>

On Thu, Apr 19, 2012 at 11:26:47PM -0700, Stephen Boyd wrote:
> complain in the case where the work is not queued. That case is not a
> false positive. We will get a lockdep warning if the work is running

IIRC, flush_work() is just a nop when a work is not queued nor running.

> (when start_flush_work() returns true) solely with the
> lock_map_acquire() on cwq->wq->lockdep_map.

Yeah, that is the point we use lockdep to detect deadlock for workqueue.

But when looking at start_flush_work(), for some case
!(cwq->wq->saved_max_active == 1 || cwq->wq->flags & WQ_RESCUER),
lock_map_acquire_read() is called, but recursive read is not added to
the chain list. So when lock_map_acquire_read(&cwq->wq->lockdep_map)
is called, deadlock will not be detected. I hope you don't hit that
special case.

Thanks,
Yong

  reply	other threads:[~2012-04-20  7:18 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-04-19  3:25 [PATCH 1/2] workqueue: Catch more locking problems with flush_work() Stephen Boyd
2012-04-19  3:25 ` [PATCH 2/2] ks8851: Fix mutex deadlock in ks8851_net_stop() Stephen Boyd
2012-04-21 19:34   ` David Miller
2012-04-19  8:10 ` [PATCH 1/2] workqueue: Catch more locking problems with flush_work() Yong Zhang
2012-04-19 18:36   ` Stephen Boyd
2012-04-20  5:26     ` Yong Zhang
2012-04-20  6:01       ` Yong Zhang
2012-04-20  6:26         ` Stephen Boyd
2012-04-20  7:18           ` Yong Zhang [this message]
2012-04-20  8:18             ` Stephen Boyd
2012-04-20  8:32               ` Yong Zhang
2012-04-21  0:32                 ` Yong Zhang
2012-04-19 15:28 ` Tejun Heo
2012-04-19 18:10   ` Stephen Boyd
2012-04-20 17:35     ` Tejun Heo
2012-04-20 23:15       ` Stephen Boyd
2012-04-21  0:28       ` [PATCHv2] " Stephen Boyd
2012-04-21  0:34         ` Yong Zhang
2012-04-23 18:07         ` Tejun Heo

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