Messages in this thread | | | Date | Wed, 5 May 2010 11:02:25 -0700 (PDT) | From | Linus Torvalds <> | Subject | Re: [PATCH 1/2] mm,migration: Prevent rmap_walk_[anon|ksm] seeing the wrong VMA information |
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On Wed, 5 May 2010, Mel Gorman wrote: > > If the same_vma list is properly ordered then maybe something like the > following is allowed?
Heh. This is the same logic I just sent out. However:
> + anon_vma = page_rmapping(page); > + if (!anon_vma) > + return NULL; > + > + spin_lock(&anon_vma->lock);
RCU should guarantee that this spin_lock() is valid, but:
> + /* > + * Get the oldest anon_vma on the list by depending on the ordering > + * of the same_vma list setup by __page_set_anon_rmap > + */ > + avc = list_entry(&anon_vma->head, struct anon_vma_chain, same_anon_vma);
We're not guaranteed that the 'anon_vma->head' list is non-empty.
Somebody could have freed the list and the anon_vma and we have a stale 'page->anon_vma' (that has just not been _released_ yet).
And shouldn't that be 'list_first_entry'? Or &anon_vma->head.next?
How did that line actually work for you? Or was it just a "it boots", but no actual testing of the rmap walk?
Linus
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