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

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Message-ID: <20140304194741.GA2204@htj.dyndns.org>
Date:	Tue, 4 Mar 2014 14:47:41 -0500
From:	Tejun Heo <tj@...nel.org>
To:	Sasha Levin <sasha.levin@...cle.com>
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 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....

Thanks.

-- 
tejun
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