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Date: Fri, 29 Mar 2013 14:48:42 +0400
From: Glauber Costa <glommer@parallels.com>
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Subject: Re: [PATCH] memcg: take reference before releasing rcu_read_lock
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To: Li Zefan <lizefan@huawei.com>
Cc: Michal Hocko <mhocko@suse.cz>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>, Johannes Weiner <hannes@cmpxchg.org>, LKML <linux-kernel@vger.kernel.org>, Cgroups <cgroups@vger.kernel.org>, linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>

On 03/29/2013 02:28 PM, Li Zefan wrote:
> The memcg is not referenced, so it can be destroyed at anytime right
> after we exit rcu read section, so it's not safe to access it.
> 
> To fix this, we call css_tryget() to get a reference while we're still
> in rcu read section.
> 
> This also removes a bogus comment above __memcg_create_cache_enqueue().
> 
Out of curiosity, did you see that happening ?

Theoretically, the race you describe seem real, and the fix is sound.

Acked-by: Glauber Costa <glommer@parallels.com>

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