btrfs: fix error handling in btrfs_del_csums

Error injection stress would sometimes fail with checksums on disk that
did not have a corresponding extent.  This occurred because the pattern
in btrfs_del_csums was

	while (1) {
		ret = btrfs_search_slot();
		if (ret < 0)
			break;
	}
	ret = 0;
out:
	btrfs_free_path(path);
	return ret;

If we got an error from btrfs_search_slot we'd clear the error because
we were breaking instead of goto out.  Instead of using goto out, simply
handle the cases where we may leave a random value in ret, and get rid
of the

	ret = 0;
out:

pattern and simply allow break to have the proper error reporting.  With
this fix we properly abort the transaction and do not commit thinking we
successfully deleted the csum.
Reviewed-by: Qu Wenruo <wqu@suse.com>
CC: stable@vger.kernel.org # 4.4+
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/file-item.c

@@ -788,7 +788,7 @@ int btrfs_del_csums(struct btrfs_trans_handle *trans,
 	u64 end_byte = bytenr + len;
 	u64 csum_end;
 	struct extent_buffer *leaf;
-	int ret;
+	int ret = 0;
 	const u32 csum_size = fs_info->csum_size;
 	u32 blocksize_bits = fs_info->sectorsize_bits;
 
@@ -806,6 +806,7 @@ int btrfs_del_csums(struct btrfs_trans_handle *trans,
 
 		ret = btrfs_search_slot(trans, root, &key, path, -1, 1);
 		if (ret > 0) {
+			ret = 0;
 			if (path->slots[0] == 0)
 				break;
 			path->slots[0]--;
@@ -862,7 +863,7 @@ int btrfs_del_csums(struct btrfs_trans_handle *trans,
 			ret = btrfs_del_items(trans, root, path,
 					      path->slots[0], del_nr);
 			if (ret)
-				goto out;
+				break;
 			if (key.offset == bytenr)
 				break;
 		} else if (key.offset < bytenr && csum_end > end_byte) {
@@ -906,8 +907,9 @@ int btrfs_del_csums(struct btrfs_trans_handle *trans,
 			ret = btrfs_split_item(trans, root, path, &key, offset);
 			if (ret && ret != -EAGAIN) {
 				btrfs_abort_transaction(trans, ret);
-				goto out;
+				break;
 			}
+			ret = 0;
 
 			key.offset = end_byte - 1;
 		} else {
@@ -917,8 +919,6 @@ int btrfs_del_csums(struct btrfs_trans_handle *trans,
 		}
 		btrfs_release_path(path);
 	}
-	ret = 0;
-out:
 	btrfs_free_path(path);
 	return ret;
 }