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

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Date:	Mon, 1 Apr 2013 11:24:13 +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 03/30/2013 04:35 AM, Li Zefan wrote:
> On 2013/3/29 18:48, Glauber Costa wrote:
>> 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 ?
>>
> 
> Just by code inspection. This is not the only place you use RCU in this
> wrong way. Remember the last patch I sent? ;)
> 
Indeed, that is what happens with miscomprehensions: the mistake tends
to be repeated. Thanks for your diligence with this.

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