linux-kernel - Re: [PATCH 05/13] mm: Make use of the anon

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Message-ID: <1270807020.20295.3299.camel@laptop>
Date:	Fri, 09 Apr 2010 11:57:00 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Christian Ehrhardt <uni@...e.de>
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 05/13] mm: Make use of the anon_vma ref count

On Fri, 2010-04-09 at 09:04 +0200, Christian Ehrhardt wrote:
> Hi,
> 
> On Thu, Apr 08, 2010 at 09:17:42PM +0200, Peter Zijlstra wrote:
> > @@ -302,23 +307,33 @@ again:
> >  		goto out;
> >  
> >  	anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON);
> > -	spin_lock(&anon_vma->lock);
> > +	if (!atomic_inc_not_zero(&anon_vma->ref))
> > +		anon_vma = NULL;
> >  
> >  	if (page_rmapping(page) != anon_vma) {
> > -		spin_unlock(&anon_vma->lock);
> > +		anon_vma_put(anon_vma);
> >  		goto again;
> >  	}
> 
> AFAICS anon_vma_put might be called with anon_vma == NULL here which
> will oops on the ref count. Not sure if
> 
>      page_rmapping(page) == anon_vma == NULL 
> 
> is possible, too.

Gah, you're right, thanks!

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