From: Michel Lespinasse <walken@google.com>
Date: Wed, 26 Sep 2012 01:33:25 +0000 (+1000)
Subject: mm: fix potential anon_vma locking issue in mprotect()
X-Git-Tag: next-20120927~1^2~307
X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=76517e721c7da6c7db0bde22e7af9c8a535bb208;p=karo-tx-linux.git

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>
---

diff --git a/mm/mmap.c b/mm/mmap.c
index 2ba27434e843..e3c365ff1b6a 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -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);