linux-kernel - Re: [PATCH] cgroup_freezer: fix freezing groups with stopped tasks

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Message-ID: <4ECB06D2.6060106@cn.fujitsu.com>
Date:	Tue, 22 Nov 2011 10:20:02 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	Tejun Heo <htejun@...il.com>
CC:	Michal Hocko <mhocko@...e.cz>, linux-kernel@...r.kernel.org,
	cgroups@...r.kernel.org, containers@...ts.linux-foundation.org,
	Tomasz Buchert <tomasz.buchert@...ia.fr>,
	Paul Menage <paul@...lmenage.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] cgroup_freezer: fix freezing groups with stopped tasks

Tejun Heo wrote:
> Hello, Michal.
> 
> On Wed, Nov 16, 2011 at 10:50:34PM +0100, Michal Hocko wrote:
>> +/* Task is frozen or will freeze immediately when next it gets woken */
>> +static bool is_task_frozen_enough(struct task_struct *task)
>> +{
>> +	return frozen(task) ||
>> +		(task_is_stopped_or_traced(task) && freezing(task));
>> +}
> 
> Hmmm... w/ pending freezer updates, the above would always return
> %true if there's freezing in progress, which can't be right.  Maybe

Only if the task is stopped/trace.

If we try to freeze a stopped task, it will be kept in freezing state.

> just test stopped/traced?
> 

This can trigger a BUG_ON in update_if_frozen(), because we always count a
stopped task as frozen.

>   http://git.kernel.org/?p=linux/kernel/git/tj/misc.git;a=shortlog;h=refs/heads/pm-freezer
> 
> Thanks.
> 
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