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Date:	Sat, 05 Apr 2008 18:40:34 +0200
From:	Soeren Sonnenburg <kernel@....de>
To:	Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>
Cc:	Linux Kernel <linux-kernel@...r.kernel.org>,
	Netdev <netdev@...r.kernel.org>
Subject: Re: 2.6.25-rc8: WARNING: at net/ipv4/tcp_input.c:2173
	tcp_mark_head_lost+0x11d/0x150()

On Fri, 2008-04-04 at 21:51 +0300, Ilpo Järvinen wrote:
> On Thu, 3 Apr 2008, Soeren Sonnenburg wrote:
> 
> > On Thu, 2008-04-03 at 16:26 +0300, Ilpo Järvinen wrote:
> > > On Thu, 3 Apr 2008, Soeren Sonnenburg wrote:
> > > 
> > > > trying to download things, I am seeing this (ignore the tainted, it is
> > > > from madwifi and although the module is loaded the device was never
> > > > used)
> > > > 
> > > > Could anyone make sense of this please?
> > > 
> > > ...I'm just trying to find out who and where invariants of the TCP code
> > > are broken. These were relatively recently enabled (pre-2.6.24 just didn't 
> > > care too much). A number of long standing issues plus bugs from my 
> > > modifications have been fixed because of the more rigid checking :-).
> > > 
> > > > ------------[ cut here ]------------
> > > > WARNING: at net/ipv4/tcp_input.c:2173 tcp_mark_head_lost+0x11d/0x150()
> > > 
> > > > ------------[ cut here ]------------
> > > > WARNING: at net/ipv4/tcp_input.c:1771 tcp_enter_frto+0x267/0x270()
> > > 
> > > > ------------[ cut here ]------------
> > > > WARNING: at net/ipv4/tcp_input.c:2532 tcp_ack+0x1a6f/0x1d60()
> > > 
> > > Can you reproduce it? 
> > 
> > Yes, by massively downloading things :-) But I have no real recipe to
> > make it easily reproducible...
> 
> Good :-), no need for recipes, just that you can trigger it more often 
> tha once per month or so :-). I probably couldn't trigger it anyway here 
> because they're often rather sensitive to network "weather", thus if you 
> have problems in reproducing, doing tests around the same phase of the 
> date cycle you saw it the first time might help.
> 
> Here's a debug patch which expensively verifies TCP's state in a number
> of places during ACK to find first spot where the actual bug occurs.

OK I am getting this now as the first spot:

P: 4 L: 2 vs 2 S: 0 vs 3 F: 0 vs 0 w: 4023500226-4023505874 (0)
skb 0 f495c180
skb 1 f480a180
skb 2 f4994600
head 3 f495c780
skb 4 f5b32480
TCP wq(s) LL  <
WARNING: at net/ipv4/tcp_ipv4.c:240 tcp_verify_wq+0x319/0x3c0()

another one:
WARNING: at net/ipv4/tcp_output.c:1475 __tcp_push_pending_frames+0x70/0x830()


P: 4 L: 2 vs 2 S: 0 vs 3 F: 0 vs 0 w: 4023500226-4023505874 (0)
skb 0 f495c180
skb 1 f480a180
skb 2 f4994600
head 3 f495c780
skb 4 f5b32480
TCP wq(s) LL  <
TCP wq(h) +-++<
l2 s3 f0 p4 seq: su4023500226 hs241530103 sn4023505874
------------[ cut here ]------------
WARNING: at net/ipv4/tcp_ipv4.c:240 tcp_verify_wq+0x319/0x3c0()

Soeren
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