Merge branch 'tcp_delack_max'

Eric Dumazet says:

====================
tcp: add tcp_delack_max()

First patches are adding const qualifiers to four existing helpers.

Third patch adds a much needed companion feature to RTAX_RTO_MIN.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/sock.h

@@ -2141,14 +2141,14 @@ static inline bool sk_rethink_txhash(struct sock *sk)
 }
 
 static inline struct dst_entry *
-__sk_dst_get(struct sock *sk)
+__sk_dst_get(const struct sock *sk)
 {
 	return rcu_dereference_check(sk->sk_dst_cache,
 				     lockdep_sock_is_held(sk));
 }
 
 static inline struct dst_entry *
-sk_dst_get(struct sock *sk)
+sk_dst_get(const struct sock *sk)
 {
 	struct dst_entry *dst;
 

include/net/tcp.h

@@ -718,8 +718,10 @@ static inline void tcp_fast_path_check(struct sock *sk)
 		tcp_fast_path_on(tp);
 }
 
+u32 tcp_delack_max(const struct sock *sk);
+
 /* Compute the actual rto_min value */
-static inline u32 tcp_rto_min(struct sock *sk)
+static inline u32 tcp_rto_min(const struct sock *sk)
 {
 	const struct dst_entry *dst = __sk_dst_get(sk);
 	u32 rto_min = inet_csk(sk)->icsk_rto_min;
@@ -729,7 +731,7 @@ static inline u32 tcp_rto_min(struct sock *sk)
 	return rto_min;
 }
 
-static inline u32 tcp_rto_min_us(struct sock *sk)
+static inline u32 tcp_rto_min_us(const struct sock *sk)
 {
 	return jiffies_to_usecs(tcp_rto_min(sk));
 }

net/ipv4/tcp.c

@@ -3762,7 +3762,8 @@ void tcp_get_info(struct sock *sk, struct tcp_info *info)
 		info->tcpi_options |= TCPI_OPT_SYN_DATA;
 
 	info->tcpi_rto = jiffies_to_usecs(icsk->icsk_rto);
-	info->tcpi_ato = jiffies_to_usecs(icsk->icsk_ack.ato);
+	info->tcpi_ato = jiffies_to_usecs(min(icsk->icsk_ack.ato,
+					      tcp_delack_max(sk)));
 	info->tcpi_snd_mss = tp->mss_cache;
 	info->tcpi_rcv_mss = icsk->icsk_ack.rcv_mss;
 

net/ipv4/tcp_output.c

@@ -3977,6 +3977,20 @@ int tcp_connect(struct sock *sk)
 }
 EXPORT_SYMBOL(tcp_connect);
 
+u32 tcp_delack_max(const struct sock *sk)
+{
+	const struct dst_entry *dst = __sk_dst_get(sk);
+	u32 delack_max = inet_csk(sk)->icsk_delack_max;
+
+	if (dst && dst_metric_locked(dst, RTAX_RTO_MIN)) {
+		u32 rto_min = dst_metric_rtt(dst, RTAX_RTO_MIN);
+		u32 delack_from_rto_min = max_t(int, 1, rto_min - 1);
+
+		delack_max = min_t(u32, delack_max, delack_from_rto_min);
+	}
+	return delack_max;
+}
+
 /* Send out a delayed ack, the caller does the policy checking
  * to see if we should even be here.  See tcp_input.c:tcp_ack_snd_check()
  * for details.
@@ -4012,7 +4026,7 @@ void tcp_send_delayed_ack(struct sock *sk)
 		ato = min(ato, max_ato);
 	}
 
-	ato = min_t(u32, ato, inet_csk(sk)->icsk_delack_max);
+	ato = min_t(u32, ato, tcp_delack_max(sk));
 
 	/* Stay within the limit we were given */
 	timeout = jiffies + ato;