Re: [PATCH 02/13] mm: Revalidate anon_vma in page_lock_anon_vma()

Rik van Riel
2010-04-08T20:51:59Z

On 04/08/2010 03:17 PM, Peter Zijlstra wrote:
> There is nothing preventing the anon_vma from being detached while we
> are spinning to acquire the lock. Most (all?) current users end up
> calling something like vma_address(page, vma) on it, which has a
> fairly good chance of weeding out wonky vmas.
>
> However suppose the anon_vma got freed and re-used while we were
> waiting to acquire the lock, and the new anon_vma fits with the
> page->index (because that is the only thing vma_address() uses to
> determine if the page fits in a particular vma, we could end up
> traversing faulty anon_vma chains.
>
> Close this hole for good by re-validating that page->mapping still
> holds the very same anon_vma pointer after we acquire the lock, if not
> be utterly paranoid and retry the whole operation (which will very
> likely bail, because it's unlikely the page got attached to a different
> anon_vma in the meantime).
>
> Signed-off-by: Peter Zijlstra<a.p.zijlstra@chello.nl>
> Cc: Hugh Dickins<hugh.dickins@tiscali.co.uk>
> Cc: Linus Torvalds<torvalds@linux-foundation.org>

Reviewed-by: Rik van Riel <riel@redhat.com>