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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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