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Date: Thu, 6 May 2010 18:40:39 -0700 (PDT)
From: Linus Torvalds <torvalds@linux-foundation.org>
To: Mel Gorman <mel@csn.ul.ie>
cc: Andrew Morton <akpm@linux-foundation.org>, Linux-MM <linux-mm@kvack.org>,
       LKML <linux-kernel@vger.kernel.org>,
       Minchan Kim <minchan.kim@gmail.com>,
       KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
       Christoph Lameter <cl@linux.com>,
       Andrea Arcangeli <aarcange@redhat.com>, Rik van Riel <riel@redhat.com>,
       Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH 2/2] mm,migration: Fix race between shift_arg_pages and
 rmap_walk by guaranteeing rmap_walk finds PTEs created within the temporary
 stack
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On Fri, 7 May 2010, Mel Gorman wrote:
> 
> Page migration requires rmap to be able to find all migration ptes
> created by migration. If the second rmap_walk clearing migration PTEs
> misses an entry, it is left dangling causing a BUG_ON to trigger during
> fault. For example;

So I still absolutely detest this patch.

Why didn't the other - much simpler - patch work? The one Rik pointed to:

	http://lkml.org/lkml/2010/4/30/198

and didn't do that _disgusting_ temporary anon_vma?

Alternatively, why don't we just take the anon_vma lock over this region, 
so that rmap can't _walk_ the damn thing?

			Linus