linux-kernel - Re: [PATCH] cgroup: missing rcu read lock around task_css

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Date:	Fri, 28 Mar 2014 10:48:17 +0800
From:	Li Zefan <lizefan@...wei.com>
To:	Sasha Levin <sasha.levin@...cle.com>
CC:	Tejun Heo <tj@...nel.org>, <containers@...ts.linux-foundation.org>,
	<cgroups@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cgroup: missing rcu read lock around task_css_set

On 2014/3/27 23:35, Sasha Levin wrote:
> On 03/04/2014 07:57 PM, Li Zefan wrote:
>> On 2014/3/5 3:47, Tejun Heo wrote:
>>> On Tue, Mar 04, 2014 at 12:20:45PM -0500, Sasha Levin wrote:
>>>>> Hrm... there is a PF_EXITING check there already:
>>>>>
>>>>>      #define task_css_set_check(task, __c)            \
>>>>>          rcu_dereference_check((task)->cgroups,        \
>>>>>          lockdep_is_held(&cgroup_mutex) ||        \
>>>>>          lockdep_is_held(&css_set_rwsem) ||        \
>>>>>          ((task)->flags & PF_EXITING) || (__c))
>>>>>
>>>>> I see it's not happening on Linus's master so I'll run a bisection to figure out what broke it.
>>>>
>>>> Hi Tejun,
>>>>
>>>> It bisects down to your patch: "cgroup: drop task_lock() protection
>>>> around task->cgroups". I'll look into it later unless it's obvious
>>>> to you.
>>>
>>> Hmmm... maybe I'm confused and PF_EXITING is not set there and
>>> task_lock was what held off the lockdep warning.  Confused....
>>>
>>
>> Because this cgroup_exit() is called in a failure path in copy_process().
> 
> It seems there was no conclusion here and it still happens in -next, anything
> we can do about it?
> 

I'll send a patch to fix it. Thanks!

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