linux-kernel - Re: Re: Race condition between putback_lru_page and mem_cgroup_move

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Message-ID: <3182585.1217908165040.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Tue, 5 Aug 2008 12:49:25 +0900 (JST)
From:	kamezawa.hiroyu@...fujitsu.com
To:	balbir@...ux.vnet.ibm.com
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	MinChan Kim <minchan.kim@...il.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	linux-mm <linux-mm@...ck.org>, Rik van Riel <riel@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Re: Race condition between putback_lru_page and mem_cgroup_move_list

>KOSAKI Motohiro wrote:
>> Hi
>> 
>>>> I think this is a race condition if mem_cgroup_move_lists's comment isn't
 right.
>>>> I am not sure that it was already known problem.
>>>>
>>>> mem_cgroup_move_lists assume the appropriate zone's lru lock is already h
eld.
>>>> but putback_lru_page calls mem_cgroup_move_lists without holding lru_lock
.
>>> Hmmm, the comment on mem_cgroup_move_lists() does say this.  Although,
>>> reading thru' the code, I can't see why it requires this.  But then it's
>>> Monday, here...
>> 
>> I also think zone's lru lock is unnecessary.
>> So, I guess below "it" indicate lock_page_cgroup, not zone lru lock.
>> 
>
>We need zone LRU lock, since the reclaim paths hold them. Not sure if I
>understand why you call zone's LRU lock unnecessary, could you elaborate plea
se?
>

I guess the comment should be against mem_cgroup_isolate_pages()...

Thanks,
-Kame

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