Fix TCP FIN handling

We can accidently spit out a huge burst of packets with TSO
when the FIN back is piggybacked onto the final packet.

[TCP]: Don't apply FIN exception to full TSO segments.
Signed-off-by: John Heffner <jheffner@psc.edu>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

net/ipv4/tcp_output.c

@@ -965,7 +965,8 @@ static inline unsigned int tcp_cwnd_test(struct tcp_sock *tp, struct sk_buff *sk
 	u32 in_flight, cwnd;
 
 	/* Don't be strict about the congestion window for the final FIN.  */
-	if (TCP_SKB_CB(skb)->flags & TCPCB_FLAG_FIN)
+	if ((TCP_SKB_CB(skb)->flags & TCPCB_FLAG_FIN) &&
+	    tcp_skb_pcount(skb) == 1)
 		return 1;
 
 	in_flight = tcp_packets_in_flight(tp);