linux-kernel - Re: [PATCH mmotm] memcg: fix mem_cgroup_update_mapped_file

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Message-Id: <20090430172727.82b1e9d2.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Thu, 30 Apr 2009 17:27:27 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	balbir@...ux.vnet.ibm.com
Cc:	Hugh Dickins <hugh@...itas.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH mmotm] memcg: fix mem_cgroup_update_mapped_file_stat
 oops

On Thu, 30 Apr 2009 10:22:40 +0530
Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:

> * KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> [2009-04-30 09:06:46]:
> 
> > On Wed, 29 Apr 2009 22:13:33 +0100 (BST)
> > Hugh Dickins <hugh@...itas.com> wrote:
> > 
> > > CONFIG_SPARSEMEM=y CONFIG_CGROUP_MEM_RES_CTLR=y cgroup_disable=memory
> > > bootup is oopsing in mem_cgroup_update_mapped_file_stat().  !SPARSEMEM
> > > is fine because its lookup_page_cgroup() contains an explicit check for
> > > NULL node_page_cgroup, but the SPARSEMEM version was missing a check for
> > > NULL section->page_cgroup.
> > > 
> > Ouch, it's curious this bug alive now.. thank you.
> > 
> > Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> > 
> > I think this patch itself is sane but.. Balbir, could you see "caller" ?
> > It seems strange.
> 
> Ideally we need to have a disabled check in
> mem_cgroup_update_mapped_file_stat(), but it seems as if this fix is
> better and fixes a larger scenario and the root cause of
> lookup_page_cgroup() OOPSing. It would not hurt to check for
> mem_cgroup_disabled() though, but too many checks might spoil the
> party for frequent operations.
> 
> Kame, do you mean you wanted me to check if I am using
> lookup_page_cgroup() correctly?
> 
Yes. I have no complaints to this patch but just curious.
Anyway thanks.

Regards,
-Kame

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