linux-kernel - Re: [-mm][PATCH 1/2] mm owner fix race between swap and exit

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Message-ID: <6599ad830808111743l58322a46u84f7af3e21467b0b@mail.gmail.com>
Date:	Mon, 11 Aug 2008 17:43:37 -0700
From:	"Paul Menage" <menage@...gle.com>
To:	"Andrew Morton" <akpm@...ux-foundation.org>
Cc:	"Balbir Singh" <balbir@...ux.vnet.ibm.com>, linux-mm@...ck.org,
	skumar@...ux.vnet.ibm.com, yamamoto@...inux.co.jp,
	lizf@...fujitsu.com, linux-kernel@...r.kernel.org,
	nishimura@....nes.nec.co.jp, xemul@...nvz.org, hugh@...itas.com,
	kamezawa.hiroyu@...fujitsu.com
Subject: Re: [-mm][PATCH 1/2] mm owner fix race between swap and exit

On Mon, Aug 11, 2008 at 5:31 PM, Andrew Morton
<akpm@...ux-foundation.org> wrote:
>> The fix is to notify the subsystem (via mm_owner_changed callback), if
>> no new owner is found by specifying the new task as NULL.
>
> This patch applies to mainline, 2.6.27-rc2 and even 2.6.26.
>
> Against which kernel/patch is it actually applicable?
>
> (If the answer was "all of the above" then please don't go embedding
> mainline bugfixes in the middle of a -mm-only patch series!)

The main thing this fixes is the memrlimit controller, which is only
in -mm. But there's also a dereference of mm->owner in memcontrol.c -
and I think that needs to be fixed to handle a possible NULL mm->owner
too, since in the case of a swapoff racing with the last user of an mm
exiting, I suspect that the swapoff code could try to pull in a page
that gets charged to the mm after its owner has been set to NULL.

Paul
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