Btrfs: fix unexpected cow in run_delalloc_nocow

commit 58113753 upstream.

Fstests generic/475 provides a way to fail metadata reads while
checking if checksum exists for the inode inside run_delalloc_nocow(),
and csum_exist_in_range() interprets error (-EIO) as inode having
checksum and makes its caller enter the cow path.

In case of free space inode, this ends up with a warning in
cow_file_range().

The same problem applies to btrfs_cross_ref_exist() since it may also
read metadata in between.

With this, run_delalloc_nocow() bails out when errors occur at the two
places.

cc: <stable@vger.kernel.org> v2.6.28+
Fixes: 17d217fe ("Btrfs: fix nodatasum handling in balancing code")
Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

fs/btrfs/inode.c

@@ -1202,6 +1202,8 @@ static noinline int csum_exist_in_range(struct btrfs_root *root,
 		list_del(&sums->list);
 		kfree(sums);
 	}
+	if (ret < 0)
+		return ret;
 	return 1;
 }
 
@@ -1351,10 +1353,23 @@ static noinline int run_delalloc_nocow(struct inode *inode,
 				goto out_check;
 			if (btrfs_extent_readonly(root, disk_bytenr))
 				goto out_check;
-			if (btrfs_cross_ref_exist(trans, root, ino,
+			ret = btrfs_cross_ref_exist(trans, root, ino,
 						  found_key.offset -
-						  extent_offset, disk_bytenr))
+						  extent_offset, disk_bytenr);
+			if (ret) {
+				/*
+				 * ret could be -EIO if the above fails to read
+				 * metadata.
+				 */
+				if (ret < 0) {
+					if (cow_start != (u64)-1)
+						cur_offset = cow_start;
+					goto error;
+				}
+
+				WARN_ON_ONCE(nolock);
 				goto out_check;
+			}
 			disk_bytenr += extent_offset;
 			disk_bytenr += cur_offset - found_key.offset;
 			num_bytes = min(end + 1, extent_end) - cur_offset;
@@ -1372,8 +1387,20 @@ static noinline int run_delalloc_nocow(struct inode *inode,
 			 * this ensure that csum for a given extent are
 			 * either valid or do not exist.
 			 */
-			if (csum_exist_in_range(root, disk_bytenr, num_bytes))
+			ret = csum_exist_in_range(root, disk_bytenr, num_bytes);
+			if (ret) {
+				/*
+				 * ret could be -EIO if the above fails to read
+				 * metadata.
+				 */
+				if (ret < 0) {
+					if (cow_start != (u64)-1)
+						cur_offset = cow_start;
+					goto error;
+				}
+				WARN_ON_ONCE(nolock);
 				goto out_check;
+			}
 			nocow = 1;
 		} else if (extent_type == BTRFS_FILE_EXTENT_INLINE) {
 			extent_end = found_key.offset +