From ca42b26ab285edc5ee3f9faa48379d258db53c35 Mon Sep 17 00:00:00 2001
From: Michel Lespinasse <walken@google.com>
Date: Mon, 8 Oct 2012 16:30:01 -0700
Subject: [PATCH] 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>
---
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