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: <20100510190559.GD22632@random.random>
Date:	Mon, 10 May 2010 21:05:59 +0200
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Mel Gorman <mel@....ul.ie>,
	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>,
	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 Mon, May 10, 2010 at 12:41:07PM -0500, Christoph Lameter wrote:
> A simple way to disallow migration of pages is to increment the refcount
> of a page.

Ok for migrate but it won't prevent to crash in split_huge_page rmap
walk, nor the PG_lock. Why for a rmap bug have a migrate specific fix?
The fix that makes execve the only special place to handle in every
rmap walk, is at least more maintainable than a fix that makes one of
the rmap walk users special and won't fix the others, as there will be
more than just 1 user that requires this. My fix didn't make execve
special and it didn't require execve knowledge into the every rmap
walk like migrate (split_huge_page etc...) but as long as the kernel
doesn't crash I'm fine ;).
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