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Subject: Re: [PATCH] cls_cgroup: Fix rcu lockdep warning
From: Peter Zijlstra <peterz@infradead.org>
To: Li Zefan <lizf@cn.fujitsu.com>
Cc: David Miller <davem@davemloft.net>,
        Herbert Xu <herbert@gondor.hengli.com.au>,
        Dave Jones <davej@redhat.com>, netdev <netdev@vger.kernel.org>,
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        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
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Date: Thu, 02 Sep 2010 12:38:36 +0200
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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.