tcp: add the ability to control max RTO

Currently, TCP stack uses a constant (120 seconds)
to limit the RTO value exponential growth.

Some applications want to set a lower value.

Add TCP_RTO_MAX_MS socket option to set a value (in ms)
between 1 and 120 seconds.

It is discouraged to change the socket rto max on a live
socket, as it might lead to unexpected disconnects.

Following patch is adding a netns sysctl to control the
default value at socket creation time.

Signed-off-by: Eric Dumazet <[email protected]>
Reviewed-by: Jason Xing <[email protected]>
Reviewed-by: Neal Cardwell <[email protected]>
Reviewed-by: Kuniyuki Iwashima <[email protected]>
Signed-off-by: Paolo Abeni <[email protected]>

1 files changed, 1 insertions, 1 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 9153fae2ebd8..4686783b70de 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -3558,7 +3558,7 @@ 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, true);