linux-kernel - Re: [PATCH cgroup/for-3.7-fixes 1/2] Revert "cgroup: Remove task_lock() from cgroup_post

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Date:	Fri, 19 Oct 2012 15:44:20 -0400
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Li Zefan <lizefan@...wei.com>,
	containers@...ts.linux-foundation.org, cgroups@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH cgroup/for-3.7-fixes 1/2] Revert "cgroup: Remove
 task_lock() from cgroup_post_fork()"

2012/10/19 Tejun Heo <tj@...nel.org>:
> On Fri, Oct 19, 2012 at 09:35:26AM -0400, Frederic Weisbecker wrote:
>> 2012/10/18 Tejun Heo <tj@...nel.org>:
>> > From d935a5d6832a264ce52f4257e176f4f96cbaf048 Mon Sep 17 00:00:00 2001
>> > From: Tejun Heo <tj@...nel.org>
>> > Date: Thu, 18 Oct 2012 17:40:30 -0700
>> >
>> > This reverts commit 7e3aa30ac8c904a706518b725c451bb486daaae9.
>> >
>> > The commit incorrectly assumed that fork path always performed
>> > threadgroup_change_begin/end() and depended on that for
>> > synchronization against task exit and cgroup migration paths instead
>> > of explicitly grabbing task_lock().
>> >
>> > threadgroup_change is not locked when forking a new process (as
>> > opposed to a new thread in the same process) and even if it were it
>> > wouldn't be effective as different processes use different threadgroup
>> > locks.
>> >
>> > Revert the incorrect optimization.
>>
>> Ok but there is still no good reason to task_lock() there. But the
>> comment is indeed wrong,  how about fixing it instead? I can send you
>> a patch for that.
>
> For -stable, I think it's better to revert.  If you want to remove
> task_lock, let's do it for 3.8.

I don't think that a wrong comment justifies a patch to stable.
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