linux-kernel - Re: race with page_referenced_one->ptep_test_and_clear

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Message-ID: <20071005155634.7d677970@cuia.boston.redhat.com>
Date:	Fri, 5 Oct 2007 15:56:34 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Hugh Dickins <hugh@...itas.com>,
	David Rientjes <rientjes@...gle.com>,
	Zachary Amsden <zach@...are.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Rusty Russell <rusty@...tcorp.com.au>, Andi Kleen <ak@...e.de>,
	Keir Fraser <keir@...source.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: race with page_referenced_one->ptep_test_and_clear_young and
 pagetable setup/pulldown

On Fri, 05 Oct 2007 12:40:05 -0700
Jeremy Fitzhardinge <jeremy@...p.org> wrote:

> Well, isn't the correct fix to make Xen take all the pagetable locks
> while pinning/unpinning?  Adding exception handling to
> test_and_clear_bit would solve this particular race, but are there
> others (either now or potentially)?  Seems fragile.

You're right, holding the pagetable lock(s) across pinning/unpinning
operations would avoid the problem too.

While we do not care about the accessed bit, there are similar operations
going on with the dirty bit - which is a lot more important :)

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