From 6c19caa3821f7eb4b481ef23e52004a9eb11c2e4 Mon Sep 17 00:00:00 2001
From: Roel Kluin <roel.kluin@gmail.com>
Date: Wed, 5 Oct 2011 11:42:29 +1100
Subject: [PATCH] btrfs: don't dereference extent_mapping if NULL

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 b2d004ad66a0..f2a18f733d4d 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -1863,7 +1863,8 @@ 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