linux-kernel - Re: [PATCH 02/14] freezer: fix a race during freezing of TASK

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Message-ID: <4CF0118B.1040708@kernel.org>
Date:	Fri, 26 Nov 2010 20:59:07 +0100
From:	Tejun Heo <tj@...nel.org>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
CC:	roland@...hat.com, oleg@...hat.com, linux-kernel@...r.kernel.org,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org
Subject: Re: [PATCH 02/14] freezer: fix a race during freezing of TASK_STOPPED
 tasks

On 11/26/2010 08:40 PM, Rafael J. Wysocki wrote:
> On Friday, November 26, 2010, Tejun Heo wrote:
>> After calling freeze_task(), try_to_freeze_tasks() see whether the
>> task is stopped or traced and if so, considers it to be frozen;
>> however, nothing guarantees that either the task being frozen sees
>> TIF_FREEZE or the freezer sees TASK_STOPPED -> TASK_RUNNING
>> transition.  The task being frozen may wake up and not see TIF_FREEZE
>> while the freezer fails to notice the transition and believes the task
>> is still stopped.
>>
>> This patch fixes the race by making freeze_task() always go through
>> fake_signal_wake_up() for applicable tasks.  The function goes through
>> the target task's scheduler lock and thus guarantees that either the
>> target sees TIF_FREEZE or try_to_freeze_task() sees TASK_RUNNING.
> 
> Looks good.  I'll take this one to my tree, if you don't mind.

Sure thing.

Thanks.

-- 
tejun
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