netdev - Re: [PATCH][v4] tcp: fix ICMP-RTO war

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Message-Id: <20100210.110843.230773162.davem@davemloft.net>
Date:	Wed, 10 Feb 2010 11:08:43 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	damian@....rwth-aachen.de
Cc:	netdev@...r.kernel.org, ilpo.jarvinen@...sinki.fi
Subject: Re: [PATCH][v4] tcp: fix ICMP-RTO war

From: Damian Lukowski <damian@....rwth-aachen.de>
Date: Wed, 10 Feb 2010 20:06:42 +0100

> Make sure, that TCP has a nonzero RTT estimation after three-way
> handshake. Currently, a listening TCP has a value of 0 for srtt,
> rttvar and rto right after the three-way handshake is completed
> with TCP timestamps disabled.
> This will lead to corrupt RTO recalculation and retransmission
> flood when RTO is recalculated on backoff reversion as introduced
> in "Revert RTO on ICMP destination unreachable"
> (f1ecd5d9e7366609d640ff4040304ea197fbc618).
> This behaviour can be provoked by connecting to a server which
> "responds first" (like SMTP) and rejecting every packet after
> the handshake with dest-unreachable, which will lead to softirq
> load on the server (up to 30% per socket in some tests).
> 
> Thanks to Ilpo Jarvinen for providing debug patches and to
> Denys Fedoryshchenko for reporting and testing.
> 
> Changes since v3: Removed bad characters in patchfile.
> 
> Reported-by: Denys Fedoryshchenko <denys@...p.net.lb>
> Signed-off-by: Damian Lukowski <damian@....rwth-aachen.de>

Thanks for doing this work, I'll study these issues
and review this patch today.
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