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SubjectRe: [PATCH 2/2] mm,migration: Prevent rmap_walk_[anon|ksm] seeing the wrong VMA information
On Mon, 26 Apr 2010 20:30:41 -0400
Rik van Riel <riel@redhat.com> wrote:

> On 04/26/2010 06:37 PM, Mel Gorman wrote:
>
> > diff --git a/mm/rmap.c b/mm/rmap.c
> > index 85f203e..bc313a6 100644
> > --- a/mm/rmap.c
> > +++ b/mm/rmap.c
> > @@ -1368,15 +1368,31 @@ static int rmap_walk_anon(struct page *page, int (*rmap_one)(struct page *,
> > * are holding mmap_sem. Users without mmap_sem are required to
> > * take a reference count to prevent the anon_vma disappearing
> > */
> > +retry:
> > anon_vma = page_anon_vma(page);
> > if (!anon_vma)
> > return ret;
> > spin_lock(&anon_vma->lock);
> > list_for_each_entry(avc,&anon_vma->head, same_anon_vma) {
> > struct vm_area_struct *vma = avc->vma;
> > - unsigned long address = vma_address(page, vma);
> > - if (address == -EFAULT)
> > - continue;
> > + unsigned long address;
> > +
> > + /*
> > + * Guard against deadlocks by not spinning against
> > + * vma->anon_vma->lock. If contention is found, release our
> > + * lock and try again until VMA list can be traversed without
> > + * contention.
> > + */
> > + if (anon_vma != vma->anon_vma) {
> > + if (!spin_trylock(&vma->anon_vma->lock)) {
> > + spin_unlock(&anon_vma->lock);
> > + goto retry;
> > + }
> > + }
>
> If you're part way down the list, surely you'll need to
> unlock multiple anon_vmas here before going to retry?
>
vma->anon_vma->lock is released after vma_address().

-Kame



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