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mm: fix potential anon_vma locking issue in mprotect() 

Fix an anon_vma locking issue in the following situation:

- vma has no anon_vma
- next has an anon_vma
- vma is being shrunk / next is being expanded, due to an mprotect call

We need to take next's anon_vma lock to avoid races with rmap users (such
as page migration) while next is being expanded.

Signed-off-by: Michel Lespinasse <walken@google.com>
Reviewed-by: Andrea Arcangeli <aarcange@redhat.com>
Acked-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Michel Lespinasse 2012-10-08 16:30:01 -07:00 committed by Linus Torvalds
parent 227e404748
commit ca42b26ab2
1 changed files with 5 additions and 1 deletions
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6
mm/mmap.c
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@ -573,8 +573,12 @@ again: remove_next = 1 + (end > next->vm_end);
*/
if (vma->anon_vma && (importer || start != vma->vm_start)) {
anon_vma = vma->anon_vma;
VM_BUG_ON(adjust_next && next->anon_vma &&
anon_vma != next->anon_vma);
} else if (adjust_next && next->anon_vma)
anon_vma = next->anon_vma;
if (anon_vma)
anon_vma_lock(anon_vma);
}
if (root) {
flush_dcache_mmap_lock(mapping);