rds: Use RCU for the bind lookup searches

The RDS bind lookups are somewhat expensive in terms of CPU
time and locking overhead.  This commit changes them into a
faster RCU based hash tree instead of the rbtrees they were using
before.

On large NUMA systems it is a significant improvement.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

net/rds/af_rds.c

@@ -72,7 +72,15 @@ static int rds_release(struct socket *sock)
 	 * with the socket. */
 	rds_clear_recv_queue(rs);
 	rds_cong_remove_socket(rs);
+
+	/*
+	 * the binding lookup hash uses rcu, we need to
+	 * make sure we sychronize_rcu before we free our
+	 * entry
+	 */
 	rds_remove_bound(rs);
+	synchronize_rcu();
+
 	rds_send_drop_to(rs, NULL);
 	rds_rdma_drop_keys(rs);
 	rds_notify_queue_get(rs, NULL);