linux-kernel - Re: [PATCH] memcg: take reference before releasing rcu_read

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Date:	Fri, 29 Mar 2013 14:48:42 +0400
From:	Glauber Costa <glommer@...allels.com>
To:	Li Zefan <lizefan@...wei.com>
CC:	Michal Hocko <mhocko@...e.cz>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Johannes Weiner <hannes@...xchg.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Cgroups <cgroups@...r.kernel.org>, <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] memcg: take reference before releasing rcu_read_lock

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@...allels.com>
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