linux-kernel - Re: Is not locking task_lock in cgroup

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Message-ID: <20121019005801.GF13370@google.com>
Date:	Thu, 18 Oct 2012 17:58:01 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Li Zefan <lizefan@...wei.com>,
	containers@...ts.linux-foundation.org, cgroups@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Is not locking task_lock in cgroup_fork() safe?

Hello, again.

On Thu, Oct 18, 2012 at 05:38:35PM -0700, Tejun Heo wrote:
> Even if there isn't an actual race, the comment is dead wrong.  I'm
> reverting the following three patches.  Let's try again later.
> 
>   7e381b0eb1 ("cgroup: Drop task_lock(parent) on cgroup_fork()")
>   7e3aa30ac8 ("cgroup: Remove task_lock() from cgroup_post_fork()")

So, after some more looking, I think the following is correct and
doesn't need to be reverted.  It's depending on threadgroup locking
from migration path to synchronize against exit path which is always
performed.

>   c84cdf75cc ("cgroup: Remove unnecessary task_lock before fetching css_set on migration")

Frederic, were you trying to say that the above commit is correct?
Li, do you agree?

Thanks.

-- 
tejun
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