linux-kernel - Re: [PATCH 1/2] cgroup: fix exit() vsrmdir() race

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Message-ID: <20130124181923.GK2373@mtj.dyndns.org>
Date:	Thu, 24 Jan 2013 10:19:23 -0800
From:	Tejun Heo <tj@...nel.org>
To:	Li Zefan <lizefan@...wei.com>
Cc:	cgroups <cgroups@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] cgroup: fix exit() vsrmdir() race

On Thu, Jan 24, 2013 at 02:43:28PM +0800, Li Zefan wrote:
> In cgroup_exit() put_css_set_taskexit() is called without any lock,
> which might lead to accessing a freed cgroup:
> 
> thread1                           thread2
> ---------------------------------------------
> exit()
>   cgroup_exit()
>     put_css_set_taskexit()
>       atomic_dec(cgrp->count);
>                                    rmdir();
>       /* not safe !! */
>       check_for_release(cgrp);
> 
> rcu_read_lock() can be used to make sure the cgroup is alive.
> 
> Signed-off-by: Li Zefan <lizefan@...wei.com>

Applying to cgroup/for-3.8-fixes w/ stable cc'd.

* Can you please add WARN_ON_ONCE(!rcu_read_lock_held()) in
  check_for_release()?

* cgroup_release_agent() seems broken too.  It's accessing cgrp after
  removing it from release_list.  Can you please fix it too?

Thanks.

-- 
tejun
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