linux-kernel - Re: [PATCH 02/13] mm: Revalidate anon_vma in page_lock_anon

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Message-ID: <4BBE41AF.5050807@redhat.com>
Date:	Thu, 08 Apr 2010 16:50:55 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	Andrea Arcangeli <aarcange@...hat.com>,
	Avi Kivity <avi@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, akpm@...ux-foundation.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	David Miller <davem@...emloft.net>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Mel Gorman <mel@....ul.ie>, Nick Piggin <npiggin@...e.de>
Subject: Re: [PATCH 02/13] mm: Revalidate anon_vma in page_lock_anon_vma()

On 04/08/2010 03:17 PM, Peter Zijlstra wrote:
> There is nothing preventing the anon_vma from being detached while we
> are spinning to acquire the lock. Most (all?) current users end up
> calling something like vma_address(page, vma) on it, which has a
> fairly good chance of weeding out wonky vmas.
>
> However suppose the anon_vma got freed and re-used while we were
> waiting to acquire the lock, and the new anon_vma fits with the
> page->index (because that is the only thing vma_address() uses to
> determine if the page fits in a particular vma, we could end up
> traversing faulty anon_vma chains.
>
> Close this hole for good by re-validating that page->mapping still
> holds the very same anon_vma pointer after we acquire the lock, if not
> be utterly paranoid and retry the whole operation (which will very
> likely bail, because it's unlikely the page got attached to a different
> anon_vma in the meantime).
>
> Signed-off-by: Peter Zijlstra<a.p.zijlstra@...llo.nl>
> Cc: Hugh Dickins<hugh.dickins@...cali.co.uk>
> Cc: Linus Torvalds<torvalds@...ux-foundation.org>

Reviewed-by: Rik van Riel <riel@...hat.com>
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