Merge branch 'tcp-allow-to-reduce-max-rto'

Eric Dumazet says:

====================
tcp: allow to reduce max RTO

This is a followup of a discussion started 6 months ago
by Jason Xing.

Some applications want to lower the time between each
retransmit attempts.

TCP_KEEPINTVL and TCP_KEEPCNT socket options don't
work around the issue.

This series adds:

- a new TCP level socket option (TCP_RTO_MAX_MS)
- a new sysctl (/proc/sys/net/ipv4/tcp_rto_max_ms)

Admins and/or applications can now change the max rto value
at their own risk.

Link: https://lore.kernel.org/netdev/20240715033118.32322-1-kerneljasonxing@gmail.com/T/
====================

Link: https://patch.msgid.link/20250207152830.2527578-1-edumazet@google.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

1 files changed, 8 insertions, 11 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 286f15e4994a..4686783b70de 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -2252,8 +2252,7 @@ static bool tcp_check_sack_reneging(struct sock *sk, int *ack_flag)
 		unsigned long delay = max(usecs_to_jiffies(tp->srtt_us >> 4),
 					  msecs_to_jiffies(10));
 
-		inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
-					  delay, TCP_RTO_MAX);
+		tcp_reset_xmit_timer(sk, ICSK_TIME_RETRANS, delay, false);
 		*ack_flag &= ~FLAG_SET_XMIT_TIMER;
 		return true;
 	}
@@ -3282,8 +3281,7 @@ void tcp_rearm_rto(struct sock *sk)
 			 */
 			rto = usecs_to_jiffies(max_t(int, delta_us, 1));
 		}
-		tcp_reset_xmit_timer(sk, ICSK_TIME_RETRANS, rto,
-				     TCP_RTO_MAX);
+		tcp_reset_xmit_timer(sk, ICSK_TIME_RETRANS, rto, true);
 	}
 }
 
@@ -3560,10 +3558,10 @@ static void tcp_ack_probe(struct sock *sk)
 		 * This function is not for random using!
 		 */
 	} else {
-		unsigned long when = tcp_probe0_when(sk, TCP_RTO_MAX);
+		unsigned long when = tcp_probe0_when(sk, tcp_rto_max(sk));
 
 		when = tcp_clamp_probe0_to_user_timeout(sk, when);
-		tcp_reset_xmit_timer(sk, ICSK_TIME_PROBE0, when, TCP_RTO_MAX);
+		tcp_reset_xmit_timer(sk, ICSK_TIME_PROBE0, when, true);
 	}
 }
 
@@ -6469,9 +6467,8 @@ static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
 		    after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt)) {
 			/* Previous FIN/ACK or RST/ACK might be ignored. */
 			if (icsk->icsk_retransmits == 0)
-				inet_csk_reset_xmit_timer(sk,
-						ICSK_TIME_RETRANS,
-						TCP_TIMEOUT_MIN, TCP_RTO_MAX);
+				tcp_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
+						     TCP_TIMEOUT_MIN, false);
 			SKB_DR_SET(reason, TCP_INVALID_ACK_SEQUENCE);
 			goto reset_and_undo;
 		}
@@ -6586,8 +6583,8 @@ consume:
 			 */
 			inet_csk_schedule_ack(sk);
 			tcp_enter_quickack_mode(sk, TCP_MAX_QUICKACKS);
-			inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
-						  TCP_DELACK_MAX, TCP_RTO_MAX);
+			tcp_reset_xmit_timer(sk, ICSK_TIME_DACK,
+					     TCP_DELACK_MAX, false);
 			goto consume;
 		}
 		tcp_send_ack(sk);