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

[Peter Zijlstra]

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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