From 91ab26f0b043c6216bc03ea73324c82f1e73d833 Mon Sep 17 00:00:00 2001
From: Roel Kluin <roel.kluin@gmail.com>
Date: Sat, 16 Jul 2011 23:30:55 +1000
Subject: [PATCH] Don't dereference em if it's NULL or an error pointer.

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Cc: Chris Mason <chris.mason@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
 fs/btrfs/inode.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index e91b097e7252..1694e378a919 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -1864,7 +1864,8 @@ static int btrfs_io_failed_hook(struct bio *failed_bio,
 
 		read_lock(&em_tree->lock);
 		em = lookup_extent_mapping(em_tree, start, failrec->len);
-		if (em->start > start || em->start + em->len < start) {
+		if (em && !IS_ERR(em) && (em->start > start ||
+					em->start + em->len < start)) {
 			free_extent_map(em);
 			em = NULL;
 		}
-- 
2.39.5