linux-kernel - Re: [PATCH 2/3] workqueue: not allow recursion run

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Message-ID: <498FD94B.7010205@cn.fujitsu.com>
Date:	Mon, 09 Feb 2009 15:20:43 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	Oleg Nesterov <oleg@...hat.com>
CC:	Peter Zijlstra <peterz@...radead.org>,
	Frédéric Weisbecker 
	<fweisbec@...il.com>, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Eric Dumazet <dada1@...mosbay.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] workqueue: not allow recursion run_workqueue

Oleg Nesterov wrote:
> On 02/06, Lai Jiangshan wrote:
>> Oleg Nesterov wrote:
>>> On 02/05, Lai Jiangshan wrote:
>>>> DEADLOCK EXAMPLE for explain my above option:
>>>>
>>>> (work_func0() and work_func1() are work callback, and they
>>>> calls flush_workqueue())
>>>>
>>>> CPU#0					CPU#1
>>>> run_workqueue()                         run_workqueue()
>>>>   work_func0()                            work_func1()
>>>>     flush_workqueue()                       flush_workqueue()
>>>>       flush_cpu_workqueue(0)                  .
>>>>       flush_cpu_workqueue(cpu#1)              flush_cpu_workqueue(cpu#0)
>>>>         waiting work_func1() in cpu#1           waiting work_func0 in cpu#0
>>>>
>>>> DEADLOCK!
>>> I am not sure. Note that when work_func0() calls run_workqueue(),
>>> it will clear cwq->current_work, so another flush_ on CPU#1 will
>>> not wait for work_func0, no?
>> cwq->current_work is changed only when
>> !list_empty(&cwq->worklist)
>> in run_workqueue().
>>
>> so cwq->current_work may not be changed.
> 
> Ah, indeed.
> 
> Thanks for correcting me!
> 
> Oleg.
> 
> 
> 
> 

Thanks,

Could you Ack these patches?

Lai.

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