RDS: TCP: Avoid rds connection churn from rogue SYNs

When a rogue SYN is received after the connection arbitration
algorithm has converged, the incoming SYN should not needlessly
quiesce the transmit path, and it should not result in needless
TCP connection resets due to re-execution of the connection
arbitration logic.
Signed-off-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/rds/tcp_listen.c

@@ -132,11 +132,13 @@ int rds_tcp_accept_one(struct socket *sock)
 		 * so we must quiesce any send threads before resetting
 		 * c_transport_data.
 		 */
-		wait_event(conn->c_waitq,
-			   !test_bit(RDS_IN_XMIT, &conn->c_flags));
-		if (ntohl(inet->inet_saddr) < ntohl(inet->inet_daddr)) {
+		if (ntohl(inet->inet_saddr) < ntohl(inet->inet_daddr) ||
+		    !conn->c_outgoing) {
 			goto rst_nsk;
-		} else if (rs_tcp->t_sock) {
+		} else {
+			atomic_set(&conn->c_state, RDS_CONN_CONNECTING);
+			wait_event(conn->c_waitq,
+				   !test_bit(RDS_IN_XMIT, &conn->c_flags));
 			rds_tcp_restore_callbacks(rs_tcp->t_sock, rs_tcp);
 			conn->c_outgoing = 0;
 		}