linux-kernel - Re: [PATCH V2] workqueue: fix possible race condition when rescuer VS pwq-release

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Message-ID: <20140416165052.GK1257@htj.dyndns.org>
Date:	Wed, 16 Apr 2014 12:50:52 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Lai Jiangshan <laijs@...fujitsu.com>
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2] workqueue: fix possible race condition when rescuer
 VS pwq-release

Hello, Lai.

On Thu, Apr 17, 2014 at 12:21:21AM +0800, Lai Jiangshan wrote:
> OK. It is better to use get_pwq(). I will also change the above comments to:
> 
>   The base ref and the possible ref from rerscuer(stopped) are never
> dropped on per-cpu pwqs.
>   Directly free the pwqs and wq.

Hmmm, why does that matter?  The base ref is the business of
create/destroy path and as long as base ref is never put other refs
just don't matter.

> The reason I quickly dropped V1 and wrote the V2 is that I saw this comment.
> "The base ref" is precise after I used get_pwq() in V1.
> 
> Or to avoid to change to this comments.
> I can also move the following code down to the bottom of the rescuer_thread().
> 
> if (kthread_should_stop()) {
> __set_current_state(TASK_RUNNING);
> rescuer->task->flags &= ~PF_WQ_WORKER;
> return 0;
> }
> 
> (I reply this email on browser, never mind the syntax).
> Maybe the second choice are better.

Hmmm... yeah, regardlesss of the above, it's a bit nasty that rescuer
may exit with non-empty mayday list.

Thanks.

-- 
tejun
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