tcp: fix ssthresh u16 leftover

It was once upon time so that snd_sthresh was a 16-bit quantity.
...That has not been true for long period of time. I run across
some ancient compares which still seem to trust such legacy.
Put all that magic into a single place, I hopefully found all
of them.

Compile tested, though linking of allyesconfig is ridiculous
nowadays it seems.
Signed-off-by: NIlpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/net/tcp.h

@@ -793,6 +793,13 @@ static inline unsigned int tcp_packets_in_flight(const struct tcp_sock *tp)
 	return tp->packets_out - tcp_left_out(tp) + tp->retrans_out;
 }
 
+#define TCP_INFINITE_SSTHRESH	0x7fffffff
+
+static inline bool tcp_in_initial_slowstart(const struct tcp_sock *tp)
+{
+	return tp->snd_ssthresh >= TCP_INFINITE_SSTHRESH;
+}
+
 /* If cwnd > ssthresh, we may raise ssthresh to be half-way to cwnd.
  * The exception is rate halving phase, when cwnd is decreasing towards
  * ssthresh.

net/ipv4/tcp.c

@@ -2012,7 +2012,7 @@ int tcp_disconnect(struct sock *sk, int flags)
 	tp->snd_cwnd = 2;
 	icsk->icsk_probes_out = 0;
 	tp->packets_out = 0;
-	tp->snd_ssthresh = 0x7fffffff;
+	tp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
 	tp->snd_cwnd_cnt = 0;
 	tp->bytes_acked = 0;
 	tcp_set_ca_state(sk, TCP_CA_Open);

net/ipv4/tcp_input.c

@@ -761,7 +761,7 @@ void tcp_update_metrics(struct sock *sk)
 			set_dst_metric_rtt(dst, RTAX_RTTVAR, var);
 		}
 
-		if (tp->snd_ssthresh >= 0xFFFF) {
+		if (tcp_in_initial_slowstart(tp)) {
 			/* Slow start still did not finish. */
 			if (dst_metric(dst, RTAX_SSTHRESH) &&
 			    !dst_metric_locked(dst, RTAX_SSTHRESH) &&

net/ipv4/tcp_ipv4.c

@@ -1808,7 +1808,7 @@ static int tcp_v4_init_sock(struct sock *sk)
 	/* See draft-stevens-tcpca-spec-01 for discussion of the
 	 * initialization of these values.
 	 */
-	tp->snd_ssthresh = 0x7fffffff;	/* Infinity */
+	tp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
 	tp->snd_cwnd_clamp = ~0;
 	tp->mss_cache = 536;
 
@@ -2284,7 +2284,7 @@ static void get_tcp4_sock(struct sock *sk, struct seq_file *f, int i, int *len)
 		jiffies_to_clock_t(icsk->icsk_ack.ato),
 		(icsk->icsk_ack.quick << 1) | icsk->icsk_ack.pingpong,
 		tp->snd_cwnd,
-		tp->snd_ssthresh >= 0xFFFF ? -1 : tp->snd_ssthresh,
+		tcp_in_initial_slowstart(tp) ? -1 : tp->snd_ssthresh,
 		len);
 }
 

net/ipv4/tcp_minisocks.c

@@ -410,7 +410,7 @@ struct sock *tcp_create_openreq_child(struct sock *sk, struct request_sock *req,
 		newtp->retrans_out = 0;
 		newtp->sacked_out = 0;
 		newtp->fackets_out = 0;
-		newtp->snd_ssthresh = 0x7fffffff;
+		newtp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
 
 		/* So many TCP implementations out there (incorrectly) count the
 		 * initial SYN frame in their delayed-ACK and congestion control

net/ipv6/tcp_ipv6.c

@@ -1846,7 +1846,7 @@ static int tcp_v6_init_sock(struct sock *sk)
 	/* See draft-stevens-tcpca-spec-01 for discussion of the
 	 * initialization of these values.
 	 */
-	tp->snd_ssthresh = 0x7fffffff;
+	tp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
 	tp->snd_cwnd_clamp = ~0;
 	tp->mss_cache = 536;
 
@@ -1969,7 +1969,8 @@ static void get_tcp6_sock(struct seq_file *seq, struct sock *sp, int i)
 		   jiffies_to_clock_t(icsk->icsk_rto),
 		   jiffies_to_clock_t(icsk->icsk_ack.ato),
 		   (icsk->icsk_ack.quick << 1 ) | icsk->icsk_ack.pingpong,
-		   tp->snd_cwnd, tp->snd_ssthresh>=0xFFFF?-1:tp->snd_ssthresh
+		   tp->snd_cwnd,
+		   tcp_in_initial_slowstart(tp) ? -1 : tp->snd_ssthresh
 		   );
 }