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tcp: avoid too many retransmit packets
If a TCP socket is using TCP_USER_TIMEOUT, and the other peer retracted its window to zero, tcp_retransmit_timer() can retransmit a packet every two jiffies (2 ms for HZ=1000), for about 4 minutes after TCP_USER_TIMEOUT has 'expired'. The fix is to make sure tcp_rtx_probe0_timed_out() takes icsk->icsk_user_timeout into account. Before blamed commit, the socket would not timeout after icsk->icsk_user_timeout, but would use standard exponential backoff for the retransmits. Also worth noting that before commite89688e3e9
("net: tcp: fix unexcepted socket die when snd_wnd is 0"), the issue would last 2 minutes instead of 4. Fixes:b701a99e43
("tcp: Add tcp_clamp_rto_to_user_timeout() helper to improve accuracy") Signed-off-by: Eric Dumazet <edumazet@google.com> Cc: Neal Cardwell <ncardwell@google.com> Reviewed-by: Jason Xing <kerneljasonxing@gmail.com> Reviewed-by: Jon Maxwell <jmaxwell37@gmail.com> Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com> Link: https://patch.msgid.link/20240710001402.2758273-1-edumazet@google.com Signed-off-by: Jakub Kicinski <kuba@kernel.org>
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@ -483,15 +483,26 @@ static bool tcp_rtx_probe0_timed_out(const struct sock *sk,
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const struct sk_buff *skb,
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u32 rtx_delta)
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{
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const struct inet_connection_sock *icsk = inet_csk(sk);
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u32 user_timeout = READ_ONCE(icsk->icsk_user_timeout);
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const struct tcp_sock *tp = tcp_sk(sk);
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const int timeout = TCP_RTO_MAX * 2;
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int timeout = TCP_RTO_MAX * 2;
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s32 rcv_delta;
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if (user_timeout) {
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/* If user application specified a TCP_USER_TIMEOUT,
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* it does not want win 0 packets to 'reset the timer'
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* while retransmits are not making progress.
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*/
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if (rtx_delta > user_timeout)
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return true;
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timeout = min_t(u32, timeout, msecs_to_jiffies(user_timeout));
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}
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/* Note: timer interrupt might have been delayed by at least one jiffy,
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* and tp->rcv_tstamp might very well have been written recently.
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* rcv_delta can thus be negative.
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*/
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rcv_delta = inet_csk(sk)->icsk_timeout - tp->rcv_tstamp;
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rcv_delta = icsk->icsk_timeout - tp->rcv_tstamp;
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if (rcv_delta <= timeout)
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return false;
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