netdev - Re: WARNING: at net/ipv4/tcp

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Date:	Mon, 28 Apr 2008 20:07:28 +0100
From:	Andy Furniss <lists@...yfurniss.entadsl.com>
To:	Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>
CC:	Netdev <netdev@...r.kernel.org>
Subject: Re: WARNING: at net/ipv4/tcp_input.c

Ilpo Järvinen wrote:
> On Mon, 28 Apr 2008, Andy Furniss wrote:
> 
>> Since upgrading to 2.6.25 from 2.6.21.1 I've noticed a few of these.
> 
> ...Thanks for the report, you could actually reproduce it in non-infinite 
> time?? ...Finally somebody who might actually have a change to catch 
> this shows up... :-)

Hopefully - grepping shows I've had a few, I was running -rc7 for a 
while and see a different message from that. I changed to .25 on the 21st.

andy@...i:~$ grep WARNING /var/log/kern.log
Mar 29 20:35:03 noki kernel: WARNING: at net/ipv4/tcp_input.c:2510 
tcp_fastretrans_alert+0x685/0x6b0()
Mar 30 03:02:04 noki kernel: WARNING: at net/ipv4/tcp_input.c:2510 
tcp_fastretrans_alert+0x685/0x6b0()
Apr 15 05:11:02 noki kernel: WARNING: at net/ipv4/tcp_input.c:2510 
tcp_fastretrans_alert+0x685/0x6b0()
Apr 19 17:11:36 noki kernel: WARNING: at net/ipv4/tcp_input.c:2510 
tcp_fastretrans_alert+0x685/0x6b0()
Apr 26 19:42:33 noki kernel: WARNING: at net/ipv4/tcp_input.c:2539 
tcp_ack+0x1dc2/0x1df0()
Apr 28 08:35:58 noki kernel: WARNING: at net/ipv4/tcp_input.c:2539 
tcp_ack+0x1dc2/0x1df0()
Apr 28 17:38:00 noki kernel: WARNING: at net/ipv4/tcp_input.c:2539 
tcp_ack+0x1dc2/0x1df0()

> I've tried to catch these with torrent but never got anything, it seems to 
> be quite sensitive to "network weather", which varies too much for me to 
> catch it. Maybe I'll try w/o timestamps if that helps me to reproduce it 
> (more likely).

Could be my qos shaking things up. bt uses piggy backed acks and I must 
drop a fair few. I probably reorder a bit as well by treating small tcp 
as higher prio than large. Egress tcp is also mss clamped to 1150.

> The debug patch below will add considerable amount of processing per ACK 
> to verify where this invariant gets broken for the first time, in case 
> that's fine with your server, please consider adding that and waiting 
> until it spits something out... :-)

No problem it's 90% idle most of the time and my wan isn't that fast.

I'll rebuild tonight.

Andy.


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