Re: [PATCH 05/13] mm: Make use of the anon_vma ref count

[Christian Ehrhardt]

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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