[TCP]: Congestion control initialization.

Change to defer congestion control initialization.

If setsockopt() was used to change TCP_CONGESTION before
connection is established, then protocols that use sequence numbers
to keep track of one RTT interval (vegas, illinois, ...) get confused.

Change the init hook to be called after handshake.
Signed-off-by: NStephen Hemminger <shemminger@linux-foundation.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/tcp_cong.c

@@ -77,18 +77,19 @@ void tcp_init_congestion_control(struct sock *sk)
 	struct inet_connection_sock *icsk = inet_csk(sk);
 	struct tcp_congestion_ops *ca;
 
-	if (icsk->icsk_ca_ops != &tcp_init_congestion_ops)
-		return;
+	/* if no choice made yet assign the current value set as default */
+	if (icsk->icsk_ca_ops == &tcp_init_congestion_ops) {
+		rcu_read_lock();
+		list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
+			if (try_module_get(ca->owner)) {
+				icsk->icsk_ca_ops = ca;
+				break;
+			}
 
-	rcu_read_lock();
-	list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
-		if (try_module_get(ca->owner)) {
-			icsk->icsk_ca_ops = ca;
-			break;
+			/* fallback to next available */
 		}
-
+		rcu_read_unlock();
 	}
-	rcu_read_unlock();
 
 	if (icsk->icsk_ca_ops->init)
 		icsk->icsk_ca_ops->init(sk);
@@ -236,6 +237,7 @@ int tcp_set_congestion_control(struct sock *sk, const char *name)
 
 	rcu_read_lock();
 	ca = tcp_ca_find(name);
+
 	/* no change asking for existing value */
 	if (ca == icsk->icsk_ca_ops)
 		goto out;
@@ -261,7 +263,8 @@ int tcp_set_congestion_control(struct sock *sk, const char *name)
 	else {
 		tcp_cleanup_congestion_control(sk);
 		icsk->icsk_ca_ops = ca;
-		if (icsk->icsk_ca_ops->init)
+
+		if (sk->sk_state != TCP_CLOSE && icsk->icsk_ca_ops->init)
 			icsk->icsk_ca_ops->init(sk);
 	}
  out: