Merge branch 'rds-conn-spamming'

Sowmini Varadhan says:

====================
RDS: TCP: connection spamming fixes

We have been testing the RDS-TCP code with a connection spammer
that sends incoming SYNs to the RDS listen port well after
an rds-tcp connection has been established, and found a few
race-windows that are fixed by this patch series.

Patch 1 avoids a null pointer deref when an incoming SYN
shows up when a netns is being dismantled, or when the
rds-tcp module is being unloaded.

Patch 2 addresses the case when a 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: David S. Miller <davem@davemloft.net>

net/rds/tcp_listen.c

@@ -80,6 +80,9 @@ int rds_tcp_accept_one(struct socket *sock)
 	int conn_state;
 	struct sock *nsk;
 
+	if (!sock) /* module unload or netns delete in progress */
+		return -ENETUNREACH;
+
 	ret = sock_create_kern(sock_net(sock->sk), sock->sk->sk_family,
 			       sock->sk->sk_type, sock->sk->sk_protocol,
 			       &new_sock);
@@ -129,11 +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;
 		}