Commit 3256a2d6 authored Sep 30, 2019 by Eric Dumazet Committed by David S. Miller Oct 01, 2019

tcp: adjust rto_base in retransmits_timed_out()



The cited commit exposed an old retransmits_timed_out() bug
which assumed it could call tcp_model_timeout() with
TCP_RTO_MIN as rto_base for all states.

But flows in SYN_SENT or SYN_RECV state uses a different
RTO base (1 sec instead of 200 ms, unless BPF choses
another value)

This caused a reduction of SYN retransmits from 6 to 4 with
the default /proc/sys/net/ipv4/tcp_syn_retries value.

Fixes: a41e8a88 ("tcp: better handle TCP_USER_TIMEOUT in SYN_SENT state")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Yuchung Cheng <ycheng@google.com>
Cc: Marek Majkowski <marek@cloudflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 0d9138ff

net/ipv4/tcp_timer.c

+7 −2

Original line number	Diff line number	Diff line
		@@ -198,8 +198,13 @@ static bool retransmits_timed_out(struct sock *sk,
		return false;

		start_ts = tcp_sk(sk)->retrans_stamp;
		if (likely(timeout == 0))
		timeout = tcp_model_timeout(sk, boundary, TCP_RTO_MIN);
		if (likely(timeout == 0)) {
		unsigned int rto_base = TCP_RTO_MIN;

		if ((1 << sk->sk_state) & (TCPF_SYN_SENT \| TCPF_SYN_RECV))
		rto_base = tcp_timeout_init(sk);
		timeout = tcp_model_timeout(sk, boundary, rto_base);
		}

		return (s32)(tcp_time_stamp(tcp_sk(sk)) - start_ts - timeout) >= 0;
		}

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