linux-kernel - Re: [PATCH] mm: fix hang on anon

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Message-ID: <1282990626.1975.3270.camel@laptop>
Date:	Sat, 28 Aug 2010 12:17:06 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Hugh Dickins <hughd@...gle.com>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH] mm: fix hang on anon_vma->root->lock

On Fri, 2010-08-27 at 21:47 -0500, Christoph Lameter wrote:
> 
> I'd be much more comfortable if the following would be done
> 
> A. Pin the anon_vma by either
>         I. Take a refcount on the anon vma

My preemptible mmu patches do that..

>         II. Take a lock in the anon vma (something that is not pointed to)
> 
> B. Either
>         I. All values that have been used before the pinning are
>            verified after the pinning (and the lock is reacquired
>            if verification fails).
> 
>         II. Or all functions using page_lock_anon_vma() must securely
>             work in the case that the anon_vma was reused for
>             something else before the vma lock was acquired.

Last time I looked they all work like that, they all use something akin
to vma_address() which validates that the page we're interested in is
indeed part of the vma we obtained from the rmap chain.

Anyway, I'll try and refresh my preemptible mmu patch-set now that the
merge window dust settled and post if again, hopefully we can stick it
in -next.
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