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: <20100504094522.GA20979@csn.ul.ie>
Date:	Tue, 4 May 2010 10:45:22 +0100
From:	Mel Gorman <mel@....ul.ie>
To:	Christoph Lameter <cl@...ux.com>
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>,
	Andrea Arcangeli <aarcange@...hat.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

On Sat, May 01, 2010 at 08:56:18PM -0500, Christoph Lameter wrote:
> On Thu, 29 Apr 2010, Mel Gorman wrote:
> 
> > There is a race between shift_arg_pages and migration that triggers this bug.
> > A temporary stack is setup during exec and later moved. If migration moves
> > a page in the temporary stack and the VMA is then removed before migration
> > completes, the migration PTE may not be found leading to a BUG when the
> > stack is faulted.
> 
> A simpler solution would be to not allow migration of the temporary stack?
> 

The patch's intention is to not migrate pages within the temporary
stack. What are you suggesting that is different?

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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