netdev - Re: [PATCH 0/3][v2] tcp: fix ICMP-RTO war

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Date:	Sun, 31 Jan 2010 23:33:38 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	damian@....rwth-aachen.de
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH 0/3][v2] tcp: fix ICMP-RTO war

From: Damian Lukowski <damian@....rwth-aachen.de>
Date: Fri, 29 Jan 2010 23:15:51 +0100

> This patches fix the current RTO calculation routine, when
> srtt and rttvar are zero, yielding an RTO of zero 
> Under some circumstances, TCPs srtt and rttvar are zero,
> yielding a calculated RTO of zero.
> This is particularly unfortunate for ICMP based RTO recalculation
> as introduced in f1ecd5d9e736660 (Revert Backoff [v3]: Revert RTO
> on ICMP destination unreachable), as it results in RTO retransmission
> flooding.
> 
> Thanks to Ilpo Jarvinen for providing debug patches and to
> Denys Fedoryshchenko for reporting and testing.
> 
> Signed-off-by: Damian Lukowski <damian@....rwth-aachen.de>

I still haven't seen a detailed enough analysis of why these
tiny RTOs can come to exist in the first place.

Please show me a list of events, function by function, the value of
relevant variables and per-socket TCP state, in the TCP stack, that
show how this ends up happening.

Thanks for all of your work on this so far.
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