Messages in this thread | | | Date | Mon, 26 Apr 2010 20:30:41 -0400 | From | Rik van Riel <> | Subject | Re: [PATCH 2/2] mm,migration: Prevent rmap_walk_[anon|ksm] seeing the wrong VMA information |
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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?
Otherwise you could forget to unlock one that you already locked, and live-lock here.
-- All rights reversed
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