[PATCH 3.16 056/366] Btrfs: fix unexpected cow in run_delalloc_nocow

[Ben Hutchings]

3.16.60-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Liu Bo <bo.li.liu@xxxxxxxxxx>

commit 5811375325420052fcadd944792a416a43072b7f 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.

Fixes: 17d217fe970d ("Btrfs: fix nodatasum handling in balancing code")
Signed-off-by: Liu Bo <bo.li.liu@xxxxxxxxxx>
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -1145,6 +1145,8 @@ static noinline int csum_exist_in_range(
 		list_del(&sums->list);
 		kfree(sums);
 	}
+	if (ret < 0)
+		return ret;
 	return 1;
 }
 
@@ -1294,10 +1296,23 @@ next_slot:
 				goto out_check;
 			if (btrfs_extent_readonly(root, disk_bytenr))
 				goto out_check;
-			if (btrfs_cross_ref_exist(trans, root, ino,
-						  found_key.offset -
-						  extent_offset, disk_bytenr))
+			ret = btrfs_cross_ref_exist(trans, root, ino,
+						    found_key.offset -
+						    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;
@@ -1315,8 +1330,22 @@ next_slot:
 			 * 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 +