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

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Message-ID: <n2p28c262361004081919qad97cc0dic538d5a23642475e@mail.gmail.com>
Date:	Fri, 9 Apr 2010 11:19:01 +0900
From:	Minchan Kim <minchan.kim@...il.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>,
	Rik van Riel <riel@...hat.com>, 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()

Hi, Peter.

On Fri, Apr 9, 2010 at 4:17 AM, Peter Zijlstra <a.p.zijlstra@...llo.nl> 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.

We have second defense rule by page_check_address.
Before anon_vma is detached, pte of pages on the anon_vma should be zeroed.
So can't page_check_address close the race?

Thanks for good trial for good feature.

-- 
Kind regards,
Minchan Kim
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