tcp: fix no cwnd growth after timeout

In commit 0f7cc9a3 "tcp: increase throughput when reordering is high",
it only allows cwnd to increase in Open state. This mistakenly disables
slow start after timeout (CA_Loss). Moreover cwnd won't grow if the
state moves from Disorder to Open later in tcp_fastretrans_alert().

Therefore the correct logic should be to allow cwnd to grow as long
as the data is received in order in Open, Loss, or even Disorder state.

Signed-off-by: Yuchung Cheng <ycheng@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/tcp_input.c

@@ -3162,16 +3162,14 @@ static inline bool tcp_may_raise_cwnd(const struct sock *sk, const int flag)
 
 	/* If reordering is high then always grow cwnd whenever data is
 	 * delivered regardless of its ordering. Otherwise stay conservative
-	 * and only grow cwnd on in-order delivery in Open state, and retain
-	 * cwnd in Disordered state (RFC5681). A stretched ACK with
+	 * and only grow cwnd on in-order delivery (RFC5681). A stretched ACK w/
 	 * new SACK or ECE mark may first advance cwnd here and later reduce
 	 * cwnd in tcp_fastretrans_alert() based on more states.
 	 */
 	if (tcp_sk(sk)->reordering > sysctl_tcp_reordering)
 		return flag & FLAG_FORWARD_PROGRESS;
 
-	return inet_csk(sk)->icsk_ca_state == TCP_CA_Open &&
-	       flag & FLAG_DATA_ACKED;
+	return flag & FLAG_DATA_ACKED;
 }
 
 /* Check that window update is acceptable.