linux-kernel - Re: [BUGFIX][PATCH] memcg: fix race in file

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Message-ID: <20100913171741.GM17950@balbir.in.ibm.com>
Date:	Mon, 13 Sep 2010 22:47:41 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Hiroyuki Kamezawa <kamezawa.hiroyuki@...il.com>
Cc:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>,
	gthelen@...gle.com,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	stable@...nel.org
Subject: Re: [BUGFIX][PATCH] memcg: fix race in file_mapped accouting flag
 management

* Hiroyuki Kamezawa <kamezawa.hiroyuki@...il.com> [2010-09-14 00:28:30]:

> > In the situation above who has the PTE lock? Are we not synchronized
> > via the PTE lock such that add rmap and rm rmap, will not happen
> > simultaneously?
> >
> In this case, a process for map and one for unmap can be different.
> 
> Assume process A maps a file cache and process B not.
> While process A unmap a file, process B can map it.
> pte lock is no help.
>

Correct, so while the accounting is correct, the flag can definitely
go wrong. I misread your race description earlier.

Thanks! 

-- 
	Three Cheers,
	Balbir
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