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

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Date:	Thu, 27 Mar 2014 11:35:09 -0400
From:	Sasha Levin <sasha.levin@...cle.com>
To:	Li Zefan <lizefan@...wei.com>, Tejun Heo <tj@...nel.org>
CC:	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 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?

Thanks,
Sasha

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