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

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Date:	Sat, 30 Mar 2013 08:35:02 +0800
From:	Li Zefan <lizefan@...wei.com>
To:	Glauber Costa <glommer@...allels.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 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? ;)

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

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