linux-kernel - Re: [PATCH v2] cgroup: Remove task_lock() from cgroup_post

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Message-ID: <4EF9206F.3090207@cn.fujitsu.com>
Date:	Tue, 27 Dec 2011 09:33:35 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	Tejun Heo <tj@...nel.org>
CC:	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Containers <containers@...ts.linux-foundation.org>,
	Cgroups <cgroups@...r.kernel.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Paul Menage <paul@...lmenage.org>,
	Mandeep Singh Baines <msb@...omium.org>
Subject: Re: [PATCH v2] cgroup: Remove task_lock() from cgroup_post_fork()

Tejun Heo wrote:
> On Fri, Dec 23, 2011 at 04:25:23AM +0100, Frederic Weisbecker wrote:
>> cgroup_post_fork() is protected between threadgroup_change_begin()
>> and threadgroup_change_end() against concurrent changes of the
>> child's css_set in cgroup_task_migrate(). Also the child can't
>> exit and call cgroup_exit() at this stage, this means it's css_set
>> can't be changed with init_css_set concurrently.
>>
>> For these reasons, we don't need to hold task_lock() on the child
>> because it's css_set can only remain stable in this place.
>>
>> Let's remove the lock there.
>>
>> v2: Update comment to explain that we are safe against
>> cgroup_exit()
>>
>> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
>> Cc: Li Zefan <lizf@...fujitsu.com>
>> Cc: Tejun Heo <tj@...nel.org>
>> Cc: Containers <containers@...ts.linux-foundation.org>
>> Cc: Cgroups <cgroups@...r.kernel.org>
>> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
>> Cc: Oleg Nesterov <oleg@...hat.com>
>> Cc: Andrew Morton <akpm@...ux-foundation.org>
>> Cc: Paul Menage <paul@...lmenage.org>
>> Cc: Mandeep Singh Baines <msb@...omium.org>
> 
> Li, does this look good to you?
> 

Acked-by: Li Zefan <lizf@...fujitsu.com>
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