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

Peter Zijlstra
2010-04-09T09:57:04Z

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!