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

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Date:	Fri, 9 Apr 2010 09:04:16 +0200
From:	Christian Ehrhardt <uni@...e.de>
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 05/13] mm: Make use of the anon_vma ref count


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.

    regards   Christian

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