code: public synchronized void releaseRebalancingPermit(int nodeId) {
          boolean removed = rebalancePermits.remove(nodeId);
          logger.info("Releasing rebalancing permit for node id " + nodeId + ", returned: " + removed);
          if(!removed)
              throw new VoldemortException(new IllegalStateException("Invalid state, must hold a "
                                                                     + "permit to release"));
      }
docs: Release the rebalancing permit for a particular node id
  
  @param nodeId The node id whose permit we want to release