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

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Message-ID: <4C766CD7.8000004@redhat.com>
Date:	Thu, 26 Aug 2010 09:32:07 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Hugh Dickins <hughd@...gle.com>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] mm: fix hang on anon_vma->root->lock

On 08/26/2010 02:12 AM, Hugh Dickins wrote:
> After several hours, kbuild tests hang with anon_vma_prepare() spinning on
> a newly allocated anon_vma's lock - on a box with CONFIG_TREE_PREEMPT_RCU=y
> (which makes this very much more likely, but it could happen without).
>
> The ever-subtle page_lock_anon_vma() now needs a further twist: since
> anon_vma_prepare() and anon_vma_fork() are liable to change the ->root
> of a reused anon_vma structure at any moment, page_lock_anon_vma()
> needs to check page_mapped() again before succeeding, otherwise
> page_unlock_anon_vma() might address a different root->lock.
>
> Signed-off-by: Hugh Dickins<hughd@...gle.com>

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

And yes, AFAIK this code lived just in -mm up to now.

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