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Commit ca42b26a authored by Michel Lespinasse's avatar Michel Lespinasse Committed by Linus Torvalds
Browse files

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: default avatarMichel Lespinasse <walken@google.com>
Reviewed-by: default avatarAndrea Arcangeli <aarcange@redhat.com>
Acked-by: default avatarHugh Dickins <hughd@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 227e4047

mm/mmap.c

+5 −1
Original line number Diff line number Diff line
@@ -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);