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    SubjectRe: [PATCH 2/3] mm,migration: Prevent rmap_walk_[anon|ksm] seeing the wrong VMA information
    On Tue, Apr 27, 2010 at 10:30:51PM +0100, Mel Gorman wrote:
    > diff --git a/mm/mmap.c b/mm/mmap.c
    > index f90ea92..61d6f1d 100644
    > --- a/mm/mmap.c
    > +++ b/mm/mmap.c
    > @@ -578,6 +578,9 @@ again: remove_next = 1 + (end > next->vm_end);
    > }
    > }
    >
    > + if (vma->anon_vma)
    > + spin_lock(&vma->anon_vma->lock);
    > +
    > if (root) {
    > flush_dcache_mmap_lock(mapping);
    > vma_prio_tree_remove(vma, root);
    > @@ -620,6 +623,9 @@ again: remove_next = 1 + (end > next->vm_end);
    > if (mapping)
    > spin_unlock(&mapping->i_mmap_lock);
    >
    > + if (vma->anon_vma)
    > + spin_unlock(&vma->anon_vma->lock);
    > +
    > if (remove_next) {
    > if (file) {
    > fput(file);

    The old code did:

    /*
    * When changing only vma->vm_end, we don't really need
    * anon_vma lock.
    */
    if (vma->anon_vma && (insert || importer || start != vma->vm_start))
    anon_vma = vma->anon_vma;
    if (anon_vma) {
    spin_lock(&anon_vma->lock);

    why did it become unconditional? (and no idea why it was removed)

    But I'm not sure about this part.... this is really only a question, I
    may well be wrong, I just don't get it.


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