netdev - Re: [PATCH net-next] tcp: fix TCP

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Date:   Wed, 24 May 2017 16:30:48 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     eric.dumazet@...il.com
Cc:     netdev@...r.kernel.org, soheil@...gle.com, ycheng@...gle.com
Subject: Re: [PATCH net-next] tcp: fix TCP_SYNCNT flakes

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Tue, 23 May 2017 12:38:35 -0700

> From: Eric Dumazet <edumazet@...gle.com>
> 
> After the mentioned commit, some of our packetdrill tests became flaky.
> 
> TCP_SYNCNT socket option can limit the number of SYN retransmits.
> 
> retransmits_timed_out() has to compare times computations based on
> local_clock() while timers are based on jiffies. With NTP adjustments
> and roundings we can observe 999 ms delay for 1000 ms timers.
> We end up sending one extra SYN packet.
> 
> Gimmick added in commit 6fa12c850314 ("Revert Backoff [v3]: Calculate
> TCP's connection close threshold as a time value") makes no
> real sense for TCP_SYN_SENT sockets where no RTO backoff can happen at
> all.
> 
> Lets use a simpler logic for TCP_SYN_SENT sockets and remove @syn_set
> parameter from retransmits_timed_out()
> 
> Fixes: 9a568de4818d ("tcp: switch TCP TS option (RFC 7323) to 1ms clock")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Signed-off-by: Yuchung Cheng <ycheng@...gle.com>

Applied, thanks Eric.