netdev - Re: tcp crash in net-2.6 tree

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Message-ID: <mFVio6um.1175336346.4693300.ijjarvin@cs.helsinki.fi>
Date:	Sat, 31 Mar 2007 13:19:06 +0300 (EEST)
From:	ijjarvin@...helsinki.fi
To:	davem@...emloft.net, tgraf@...g.ch
CC:	"ilpo.jarvinen@...sinki.fi" <ilpo.jarvinen@...sinki.fi>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: tcp crash in net-2.6 tree


On 3/31/2007, "David Miller" <davem@...emloft.net> wrote:
> From: Thomas Graf <tgraf@...g.ch>
> Date: Sat, 31 Mar 2007 00:10:54 +0200
> 
> > * David Miller <davem@...emloft.net> 2007-03-30 14:43
> > > Let's not speculate, let's find out for sure if snd_una is
> > > surpassing high_seq while we're in this state.
> > >
> > > Andrew please give this debugging patch a spin, and also what
> > > is your workload?  I'd like to play with it too.
> > >
> > > I've tried to code this patch so that if the bug triggers your
> > > machine shouldn't crash and burn completely, just spit out the
> > > log message.
> >
> > I'm running into the same bug as Andew, i was able to reproduce
> > using Dave's patch within minutes:
> >
> > TCP BUG: high_seq==NULL [c3c9cc54] q[c3c94edc] t[c3c9cc54]
> >
> > The after(snd_una, high_seq) check is not triggered.
> 
> So tp->high_seq points to the tail packet end sequence.
> 
> Ilpo does this clear things up?

Thanks for the info.

I think that the if condition before the write_queue_find should check if
skb is valid before doing after(TCP_SKB_CB(skb)->seq, tp->high_seq), it
is pointing to sk_write_queue rather than a valid skb when the previous
loop exits (there might be a similar problem later in the code too). I
apologize I cannot provide a good patch at this point of time because I
moved on Thursday and the ISP hasn't yet activated the access link
(writing this from a library machine).

--
 i.
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