From: Li Zefan <lizf@cn.fujitsu.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: David Miller <davem@davemloft.net>,
Herbert Xu <herbert@gondor.hengli.com.au>,
Dave Jones <davej@redhat.com>, netdev <netdev@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: Re: [PATCH] cls_cgroup: Fix rcu lockdep warning
Date: Fri, 03 Sep 2010 09:10:00 +0800 [thread overview]
Message-ID: <4C804AE8.1090203@cn.fujitsu.com> (raw)
In-Reply-To: <1283423916.2059.1847.camel@laptop>
Peter Zijlstra wrote:
> On Thu, 2010-09-02 at 14:30 +0800, Li Zefan wrote:
>> Calling task_subsys_state() without holding rcu_read_lock or
>> cgroup_mutex can cause lockdep warning.
>>
>
> That is not a suitable changelog.
>
> Was the warning correct? Is your patch correct? What does RCU protect
> here and why can we use classid after dropping it.
>
> Simply frobbing code to make the warning go away is not good.
>
>
task->cgroups and task->cgroups->subsys[i] are protected by RCU.
So we avoid accessing invalid pointers here. This can happen,
for example, when you are deref those pointers while someone move
@task from one cgroup to another.
otoh, there is no lock rule for ->classid.
next prev parent reply other threads:[~2010-09-03 1:10 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-09-02 6:30 [PATCH] cls_cgroup: Fix rcu lockdep warning Li Zefan
2010-09-02 10:38 ` Peter Zijlstra
2010-09-02 17:05 ` David Miller
2010-09-02 17:16 ` Paul E. McKenney
2010-09-03 1:10 ` Li Zefan [this message]
2010-09-03 4:52 ` Herbert Xu
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