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

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Message-ID: <20111223230013.GV17084@google.com>
Date:	Fri, 23 Dec 2011 15:00:13 -0800
From:	Tejun Heo <tj@...nel.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Li Zefan <lizf@...fujitsu.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()

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?

Thanks.

-- 
tejun
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