linux-kernel - Re: [PATCH 2/2] mm,migration: Avoid race between shift_arg_pages() and rmap_walk() during migration by not migrating temporary stacks

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Message-ID: <20100429162120.GC22108@random.random>
Date:	Thu, 29 Apr 2010 18:21:20 +0200
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	Mel Gorman <mel@....ul.ie>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Minchan Kim <minchan.kim@...il.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Christoph Lameter <cl@...ux.com>,
	Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH 2/2] mm,migration: Avoid race between shift_arg_pages()
 and rmap_walk() during migration by not migrating temporary stacks

Hi Mel,

did you see my proposed fix? I'm running with it applied, I'd be
interested if you can test it. Surely it will also work for new
anon-vma code in upstream, because at that point there's just 1
anon-vma and nothing else attached to the vma.

http://git.kernel.org/?p=linux/kernel/git/andrea/aa.git;a=commit;h=6efa1dfa5152ef8d7f26beb188d6877525a9dd03

I think it's wrong to try to handle the race in rmap walk by making
magic checks on vm_flags VM_GROWSDOWN|GROWSUP and
vma->vm_mm->map_count == 1, when we can fix it fully and simply in
exec.c by indexing two vmas in the same anon-vma with a different
vm_start so the pages will be found at all times by the rmap_walk.
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