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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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