We present a new concurrent B^link-tree algorithm that provides a concurrent tree restructuring mechanism for handling underflow nodes as well as overflow nodes. Our algorithm does not require any lock for downward searching and preserves bottom-up tree restructuring without deadlock. To this end, we develop a new locking mechanism for inserters and deleters and a node update rule that preserves the semantical tree consistency during tree restructuring. Our analytical experiment shows that the overhead of additional disk I/O is acceptable.