Commit ca42b26a authored Oct 08, 2012 by Michel Lespinasse Committed by Linus Torvalds Oct 09, 2012

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>

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);

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