From d83e277a101d82286748bf8d7385bcd065c701c9 Mon Sep 17 00:00:00 2001
From: Mel Gorman <mel@csn.ul.ie>
Date: Mon, 24 May 2010 14:32:19 -0700
Subject: [PATCH] --- yaml --- r: 198239 b: refs/heads/master c:
 67b9509b2c68ae38cecb83a239881cb0ddf087dc h: refs/heads/master i:   198237:
 5a639abd0da5a559182465258f8974dc1ea3f2db   198235:
 b85fa9c0d2efbb529189a23605c3927fe1836608   198231:
 0b70a64e2546f44aaf37523634c89cf0bccad8bf   198223:
 a6ae2c77ee79552c4e1cc5c151d3a821e1ae9ab3   198207:
 8996e928b519fc285b4a0af84240dc8f97143e0d v: v3

---
 [refs]             |  2 +-
 trunk/mm/migrate.c | 11 +++++++++++
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/[refs] b/[refs]
index af1843fd61ca..b715a7820701 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 7f60c214fd3a360461f3286c6908084f7f8b1950
+refs/heads/master: 67b9509b2c68ae38cecb83a239881cb0ddf087dc
diff --git a/trunk/mm/migrate.c b/trunk/mm/migrate.c
index 42a3d24d1107..b114635962dc 100644
--- a/trunk/mm/migrate.c
+++ b/trunk/mm/migrate.c
@@ -600,6 +600,17 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private,
 	if (PageAnon(page)) {
 		rcu_read_lock();
 		rcu_locked = 1;
+
+		/*
+		 * If the page has no mappings any more, just bail. An
+		 * unmapped anon page is likely to be freed soon but worse,
+		 * it's possible its anon_vma disappeared between when
+		 * the page was isolated and when we reached here while
+		 * the RCU lock was not held
+		 */
+		if (!page_mapped(page))
+			goto rcu_unlock;
+
 		anon_vma = page_anon_vma(page);
 		atomic_inc(&anon_vma->external_refcount);
 	}