linux-kernel - Re: [PATCH] mm: fix corner case in anon

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Date:	Sun, 11 Jan 2015 09:25:02 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Konstantin Khlebnikov <koct9i@...il.com>, linux-mm@...ck.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
CC:	"Elifaz, Dana" <Dana.Elifaz@....com>,
	"Bridgman, John" <John.Bridgman@....com>,
	Daniel Forrest <dan.forrest@...c.wisc.edu>,
	Chris Clayton <chris2553@...glemail.com>,
	Oded Gabbay <oded.gabbay@....com>,
	Michal Hocko <mhocko@...e.cz>
Subject: Re: [PATCH] mm: fix corner case in anon_vma endless growing prevention

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On 01/11/2015 08:54 AM, Konstantin Khlebnikov wrote:
> Fix for BUG_ON(anon_vma->degree) splashes in unlink_anon_vmas() 
> ("kernel BUG at mm/rmap.c:399!").
> 
> Anon_vma_clone() is usually called for a copy of source vma in
> destination argument. If source vma has anon_vma it should be
> already in dst->anon_vma. NULL in dst->anon_vma is used as a sign
> that it's called from anon_vma_fork(). In this case
> anon_vma_clone() finds anon_vma for reusing.
> 
> Vma_adjust() calls it differently and this breaks anon_vma reusing
> logic: anon_vma_clone() links vma to old anon_vma and updates
> degree counters but vma_adjust() overrides vma->anon_vma right
> after that. As a result final unlink_anon_vmas() decrements degree
> for wrong anon_vma.
> 
> This patch assigns ->anon_vma before calling anon_vma_clone().
> 
> Signed-off-by: Konstantin Khlebnikov <koct9i@...il.com> Fixes:
> 7a3ef208e662 ("mm: prevent endless growth of anon_vma hierarchy") 
> Tested-by: Chris Clayton <chris2553@...glemail.com> Tested-by: Oded
> Gabbay <oded.gabbay@....com> Cc: Daniel Forrest
> <dan.forrest@...c.wisc.edu> Cc: Michal Hocko <mhocko@...e.cz> Cc:
> Rik van Riel <riel@...hat.com>

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

- -- 
All rights reversed
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