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Message-ID: <53160B6D.8020501@oracle.com>
Date: Tue, 04 Mar 2014 12:20:45 -0500
From: Sasha Levin <sasha.levin@...cle.com>
To: Tejun Heo <tj@...nel.org>
CC: lizefan@...wei.com, 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 03/03/2014 06:00 PM, Sasha Levin wrote:
> On 03/03/2014 05:45 PM, Tejun Heo wrote:
>> On Mon, Mar 03, 2014 at 05:43:11PM -0500, Sasha Levin wrote:
>>> On 03/03/2014 05:33 PM, Tejun Heo wrote:
>>>> On Sat, Mar 01, 2014 at 10:00:11PM -0500, Sasha Levin wrote:
>>>>> rcu read lock should be held when calling and working with task_css_set.
>>>>>
>>>>> This patch also fixes a related lockdep warning.
>>>>
>>>> Hmmm... PF_EXITING should be visible at that point and cset can't
>>>> change anymore. We prolly need to update lockdep annotation rather
>>>> than adding spurious rcu locking around it. Against which branch is
>>>> it? Can you please post the lockdep warning?
>>>
>>> I see it on -next.
>>
>> I think the right thing to do is using task_css_set_check() with
>> PF_EXITING check and add comment explaining that cset can no longer
>> change. Can you please write up a patch?
>
> 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.
Thanks,
Sasha
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