btrfs: do not BUG_ON() on tree mod log failures at push_nodes_for_insert()

At push_nodes_for_insert(), instead of doing a BUG_ON() in case we fail to
record tree mod log operations, do a transaction abort and return the
error to the caller. There's really no need for the BUG_ON() as we can
release all resources in this context, and we have to abort because other
future tree searches that use the tree mod log (btrfs_search_old_slot())
may get inconsistent results if other operations modify the tree after
that failure and before the tree mod log based search.

Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

Author: fdmanana

fs/btrfs/ctree.c

@@ -1308,7 +1308,12 @@ static noinline int push_nodes_for_insert(struct btrfs_trans_handle *trans,
 			btrfs_node_key(mid, &disk_key, 0);
 			ret = btrfs_tree_mod_log_insert_key(parent, pslot,
 					BTRFS_MOD_LOG_KEY_REPLACE);
-			BUG_ON(ret < 0);
+			if (ret < 0) {
+				btrfs_tree_unlock(left);
+				free_extent_buffer(left);
+				btrfs_abort_transaction(trans, ret);
+				return ret;
+			}
 			btrfs_set_node_key(parent, &disk_key, pslot);
 			btrfs_mark_buffer_dirty(parent);
 			if (btrfs_header_nritems(left) > orig_slot) {
@@ -1363,7 +1368,12 @@ static noinline int push_nodes_for_insert(struct btrfs_trans_handle *trans,
 			btrfs_node_key(right, &disk_key, 0);
 			ret = btrfs_tree_mod_log_insert_key(parent, pslot + 1,
 					BTRFS_MOD_LOG_KEY_REPLACE);
-			BUG_ON(ret < 0);
+			if (ret < 0) {
+				btrfs_tree_unlock(right);
+				free_extent_buffer(right);
+				btrfs_abort_transaction(trans, ret);
+				return ret;
+			}
 			btrfs_set_node_key(parent, &disk_key, pslot + 1);
 			btrfs_mark_buffer_dirty(parent);