linux-kernel - Re: [BUGFIX][mm][PATCH] fix migration race in rmap

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Message-ID: <r2o28c262361004260248s62729484g14a720d37d5916f7@mail.gmail.com>
Date:	Mon, 26 Apr 2010 18:48:42 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Mel Gorman <mel@....ul.ie>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Christoph Lameter <cl@...ux.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [BUGFIX][mm][PATCH] fix migration race in rmap_walk

On Mon, Apr 26, 2010 at 6:28 PM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@...fujitsu.com> wrote:
> On Mon, 26 Apr 2010 08:49:01 +0900
> KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
>
>> On Sat, 24 Apr 2010 11:43:24 +0100
>> Mel Gorman <mel@....ul.ie> wrote:
>
>> > It looks nice but it still broke after 28 hours of running. The
>> > seq-counter is still insufficient to catch all changes that are made to
>> > the list. I'm beginning to wonder if a) this really can be fully safely
>> > locked with the anon_vma changes and b) if it has to be a spinlock to
>> > catch the majority of cases but still a lazy cleanup if there happens to
>> > be a race. It's unsatisfactory and I'm expecting I'll either have some
>> > insight to the new anon_vma changes that allow it to be locked or Rik
>> > knows how to restore the original behaviour which as Andrea pointed out
>> > was safe.
>> >
>> Ouch.
>
> Ok, reproduced. Here is status in my test + printk().
>
>  * A race doesn't seem to happen if swap=off.
>    I need to swapon to cause the bug

FYI,

Do you have a swapon/off bomb test?
When I saw your mail, I feel it might be culprit.

http://lkml.org/lkml/2010/4/22/762.

It is just guessing. I don't have a time to look into, now.

-- 
Kind regards,
Minchan Kim
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