ext4: return ENOMEM if sb_getblk() fails

commit 860d21e2c585f7ee8a4ecc06f474fdc33c9474f4 upstream.

The only reason for sb_getblk() failing is if it can't allocate the
buffer_head.  So ENOMEM is more appropriate than EIO.  In addition,
make sure that the file system is marked as being inconsistent if
sb_getblk() fails.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
[xr: Backported to 3.4:
 - Drop change to inline.c
 - Call to ext4_ext_check() from ext4_ext_find_extent() is conditional]
Signed-off-by: Rui Xiang <rui.xiang@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/ext4/mmp.c b/fs/ext4/mmp.c
index ed6548d..444b701 100644
--- a/fs/ext4/mmp.c
+++ b/fs/ext4/mmp.c
@@ -41,6 +41,8 @@
 	 * is not blocked in the elevator. */
 	if (!*bh)
 		*bh = sb_getblk(sb, mmp_block);
+	if (!*bh)
+		return -ENOMEM;
 	if (*bh) {
 		get_bh(*bh);
 		lock_buffer(*bh);