btrfs: abort the transaction if we get an error during snapshot drop

We were seeing weird errors when we were testing our btrfs backports
before we had the incorrect level check fix.  These errors appeared to
be improper error handling, but error injection testing uncovered that
the errors were a result of corruption that occurred from improper error
handling during snapshot delete.

With snapshot delete if we encounter any errors during walk_down or
walk_up we'll simply return an error, we won't abort the transaction.
This is problematic because we will be dropping references for nodes and
leaves along the way, and if we fail in the middle we will leave the
file system corrupt because we don't know where we left off in the drop.

Fix this by making sure we abort if we hit any errors during the walk
down or walk up operations, as we have no idea what operations could
have been left half done at this point.

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/extent-tree.c

@@ -5708,12 +5708,14 @@ int btrfs_drop_snapshot(struct btrfs_root *root, int update_ref, int for_reloc)
 
 		ret = walk_down_tree(trans, root, path, wc);
 		if (ret < 0) {
+			btrfs_abort_transaction(trans, ret);
 			err = ret;
 			break;
 		}
 
 		ret = walk_up_tree(trans, root, path, wc, BTRFS_MAX_LEVEL);
 		if (ret < 0) {
+			btrfs_abort_transaction(trans, ret);
 			err = ret;
 			break;
 		}