linux-kernel - regression(?): starting with 2.6.21 sending packets became broken.

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Message-Id: <1192299385.31908.8.camel@localhost>
Date:	Sat, 13 Oct 2007 22:16:25 +0400
From:	Peter Volkov <pva@...too.org>
To:	linux-kernel@...r.kernel.org
Subject: regression(?): starting with 2.6.21 sending packets became broken.

Hello, all on the list.

Please CC me in answers, I'm not subscribed. Please, if this is wrong
list tell me what is correct.

Starting with 2.6.21 (or may be 2.6.20 as I have not tried it) kernel I
have problem that most tcp based services freeze at some point of
operation. I've noticed this first on ssh but then found out that at
lease one other service became similarly. The problem sites somewhere in
the kernel as I've compiled 2.6.19, 2.6.21, and 2.6.22 with the
similar .config options (of course not exact, as some options does not
exist in some kernels, but seems that enabled options are all the same)
but I have this problem only with the 21 and 22. I've tried to debug the
problem a bit, but not a lot as that is production box working as linux
based firewall/router.

First I took tcpdump. Although ssh connection to the router is not
always possible as it often hangs before I get into router, after some
attempts ssh connection was established. On client computer I've started
tcpdump and worked a bit until hang. tcpdump output showed me that when
I press any keys the packets are sent to the server and proper ack are
received. Later I found that all commands I enter blindly are executed
on router but I receive no reply packets with some data in them (pure
ack). That's why nothing happens on the screen and it looks like
hanging.

Now I've got to the router started ssh connection from router to some
other server. It hanged too. I attached strace and found that ssh
receive keyboard pressings (read() calls in the output) and writes them
further to the kernel (write() calls) but tcpdump on the router shows no
packets. So packets enter kernel and lost somewhere inside.

Now a information about my system. That's a pentium4 system with
hyper-threading enabled. cpuinfo and lspci output attached. kernel built
with "gcc version 4.1.2 (Gentoo 4.1.2 p1.0.2)" and binutils version
2.17. My .config file for all kernels I've mentioned is available here:

http://theor.ran.gpi.ru/linux-2.6.19-gentoo-r5-config (works)
http://theor.ran.gpi.ru/linux-2.6.21-gentoo-r4-config (not works)
http://theor.ran.gpi.ru/linux-2.6.22-gentoo-r8-config (not works)

Besides standard gentoo patchsets all kernels have IMQ and IPSET's
patches.

Does anybody have any idea what's going on with the latest kernels? How
to debug it further?

-- 
Peter.

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