netdev - Re: [PATCH v3] tcp: don't ignore ECN CWR on pure ACK

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Message-Id: <20200625.122212.1431059494499957023.davem@davemloft.net>
Date:   Thu, 25 Jun 2020 12:22:12 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     kda@...ux-powerpc.org
Cc:     netdev@...r.kernel.org, ncardwell@...gle.com, edumazet@...gle.com,
        ycheng@...gle.com, Richard.Scheffenegger@...app.com,
        ietf@...briscoe.net
Subject: Re: [PATCH v3] tcp: don't ignore ECN CWR on pure ACK

From: Denis Kirjanov <kda@...ux-powerpc.org>
Date: Thu, 25 Jun 2020 14:51:06 +0300

> there is a problem with the CWR flag set in an incoming ACK segment
> and it leads to the situation when the ECE flag is latched forever
> 
> the following packetdrill script shows what happens:
 ...
> In the situation above we will continue to send ECN ECHO packets
> and trigger the peer to reduce the congestion window. To avoid that
> we can check CWR on pure ACKs received.
> 
> v3:
> - Add a sequence check to avoid sending an ACK to an ACK
> 
> v2:
> - Adjusted the comment
> - move CWR check before checking for unacknowledged packets
> 
> Signed-off-by: Denis Kirjanov <denis.kirjanov@...e.com>

Applied, thanks.