Fwd: Problems with ipv4 part of Kernels post-2.6.16

Sorry - reply-all got a bounce, didn't check the bad netdev address...

---------- Forwarded message ----------
From: Alessandro Suardi <redacted>
Date: Sep 4, 2006 12:07 AM
Subject: Re: Problems with ipv4 part of Kernels post-2.6.16
To: Willy Tarreau <w@1wt.eu>
Cc: Rogério Brito <redacted>, linux-kernel@vger.kernel.org,
linux-netdev@vger.kernel.org, John Heffner [off-list ref], "David
S. Miller" [off-list ref]


On 9/3/06, Willy Tarreau [off-list ref] wrote:

Hi Rogério,

On Sun, Sep 03, 2006 at 05:13:35PM -0300, Rogério Brito wrote:

quoted

Hi, John, David and others developers.

I have been trying to keep up with the kernel releases (not only the
-rc ones, but also some -mm's) and I noticed something quite strange:
with some post 2.6.16 kernels (say, 2.6.17), I can't access (from where
I am) the site www.everymac.com, while I can access other sites.

I believe I read on LKML last month that there's a problem on this site
with window scaling. There's a patch floating around to allow per
destination window clamping. I believe that you can workaround the
problem by disabling TCP window scaling :

   echo 0 >/proc/sys/net/ipv4/tcp_window_scaling

Hoping this helps,
Willy

The above does help while hitting certain websites from behind my
 corporate proxy (while others are okay); same websites can be
 accessed without any issue from my home ISP connection.

I logged an internal ticket for this, will check whether there's been
 any update as of recently; both happens with recent 2.6.18-rc and
 with FC5-latest kernel.

quoted

This has made me quite curious, because just booting back with a
2.6.16.x kernel, I could access it, which, of course, led me to think
this was a problem with the networking part of the kernel.

Well, to cut a long story short, yesterday I decided to learn how to use
git, grabbed Linus's tree and started a bisection session.

After 12 recompilations, I found the following patch being the first
suspect (sorry for the line wrapping, but I copied this one from one
console to another, since I don't know how to generate it again with
git):

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
rbrito@dumont:/usr/local/media/progs/linux/kernel/linux-git$ git bisect
good
7b4f4b5ebceab67ce440a61081a69f0265e17c2a is first bad commit
commit 7b4f4b5ebceab67ce440a61081a69f0265e17c2a
Author: John Heffner [off-list ref]
Date:   Sat Mar 25 01:34:07 2006 -0800

    [TCP]: Set default max buffers from memory pool size

    This patch sets the maximum TCP buffer sizes (available to automatic
    buffer tuning, not to setsockopt) based on the TCP memory pool size.
    The maximum sndbuf and rcvbuf each will be up to 4 MB, but no more
    than 1/128 of the memory pressure threshold.

    Signed-off-by: John Heffner [off-list ref]
    Signed-off-by: David S. Miller [off-list ref]

:040000 040000 514849b6a38c5fb671f3aeae1c0108a0e8e897dc
3b912fd10db444b22262f995fac99f2851363531 M      net
rbrito@dumont:/usr/local/media/progs/linux/kernel/linux-git$
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

I'm currently connected to my provider via cable modem and I'm assigned
an IP address via DHCP (actually, I'm using a D-Link DI-524 router in
between, but I already tested *without* the router in the middle and the
problem remains). The contents of my /etc/sysctl.conf file are attached.

My userspace is Debian's testing/etch, regularly upgraded every day. My
system is a Duron 1.1GHz, with 512MB of RAM and a KT133 (VIA) chipset,
with the network card being a Realtek RTL8139.

I would like to point out that this has prevented me from using/testing
other newer kernels. :-(

If anything else is required, please, don't hesitate to ask. I will try
my best to use any patches that may seem relevant, until we can point
out what may be happening.


Thanks, Rogério Brito.

P.S.: Please, I'm not (currently) subscribed to any mailing list.  I'd
appreciate if the CCs weren't trimmed.
--
Rogério Brito : rbrito@ime.usp.br : http://www.ime.usp.br/~rbrito
Homepage of the algorithms package : http://algorithms.berlios.de
Homepage on freshmeat:  http://freshmeat.net/projects/algorithms/

quoted

#
# /etc/sysctl.conf - Configuration file for setting system variables
# See sysctl.conf (5) for information.
#

# Uncomment the following to stop low-level messages on console
#kernel.printk = 4 4 1 7

##############################################################3
# Functions previously found in netbase
#
#net.ipv4.conf.default.forwarding=1
#net.ipv6.conf.default.forwarding=1

dev.rtc.max-user-freq=1024
net.ipv4.conf.all.accept_redirects=0
net.ipv4.conf.all.accept_source_route=0
net.ipv4.conf.all.log_martians=1
net.ipv4.conf.all.rp_filter=1
net.ipv4.conf.default.accept_redirects=0
net.ipv4.conf.default.accept_source_route=0
net.ipv4.conf.default.log_martians=1
net.ipv4.conf.default.rp_filter=1
net.ipv4.icmp_echo_ignore_broadcasts=1
net.ipv4.tcp_syncookies=1

--alessandro

"What's the name of the word for the precise moment when you
 realize that you've actually forgotten how it felt to make love
 to somebody you really liked a long time ago?"
"There isn't one."
"Oh. I thought maybe there was."
     (The Sandman, dialogue between Delirium and Dream)


-- 
--alessandro

"What's the name of the word for the precise moment when you
 realize that you've actually forgotten how it felt to make love
 to somebody you really liked a long time ago?"
"There isn't one."
"Oh. I thought maybe there was."
     (The Sandman, dialogue between Delirium and Dream)

-- 
VGER BF report: H 3.88436e-05