netdev - Re: [PATCH net] tcp: better handle TCP_USER_TIMEOUT in SYN

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Date:   Fri, 27 Sep 2019 20:42:55 +0200 (CEST)
From:   David Miller <davem@...emloft.net>
To:     edumazet@...gle.com
Cc:     netdev@...r.kernel.org, eric.dumazet@...il.com, ycheng@...gle.com,
        marek@...udflare.com, jmaxwell37@...il.com
Subject: Re: [PATCH net] tcp: better handle TCP_USER_TIMEOUT in SYN_SENT
 state

From: Eric Dumazet <edumazet@...gle.com>
Date: Thu, 26 Sep 2019 15:42:51 -0700

> Yuchung Cheng and Marek Majkowski independently reported a weird
> behavior of TCP_USER_TIMEOUT option when used at connect() time.
> 
> When the TCP_USER_TIMEOUT is reached, tcp_write_timeout()
> believes the flow should live, and the following condition
> in tcp_clamp_rto_to_user_timeout() programs one jiffie timers :
> 
>     remaining = icsk->icsk_user_timeout - elapsed;
>     if (remaining <= 0)
>         return 1; /* user timeout has passed; fire ASAP */
> 
> This silly situation ends when the max syn rtx count is reached.
> 
> This patch makes sure we honor both TCP_SYNCNT and TCP_USER_TIMEOUT,
> avoiding these spurious SYN packets.
> 
> Fixes: b701a99e431d ("tcp: Add tcp_clamp_rto_to_user_timeout() helper to improve accuracy")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reported-by: Yuchung Cheng <ycheng@...gle.com>
> Reported-by: Marek Majkowski <marek@...udflare.com>
> Cc: Jon Maxwell <jmaxwell37@...il.com>
> Link: https://marc.info/?l=linux-netdev&m=156940118307949&w=2

Applied and queued up for -stable.