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To: davidg@root.com
cc: current@freebsd.org, "Garrett A. Wollman" <wollman@lcs.mit.edu>
Subject: Re: m_copydata panic & tcp_extensions: some results 
In-reply-to: Your message of "Wed, 03 Jan 1996 09:15:21 PST."
             <199601031716.JAA00406@corbin.Root.COM> 
Date: Thu, 04 Jan 1996 18:44:37 +0100
Message-ID: <19542.820777477@curie.cs.utwente.nl>
From: Andras Olah <olah@cs.utwente.nl>
Sender: owner-current@freebsd.org
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On Wed, 03 Jan 1996 09:15:21 PST, David Greenman wrote:
> >In several days I don't have such panic after disabling
> >tcp_extensions, David's guess was right.
> 
>    Okay. I think the problems started happening when Andras fixed some bugs
> related to T/TCP...but I might be wrong.

I think I've found the source of the bug which is likely to be
caused by the following change:

> olah        95/11/03 14:19:52
> 
>   Modified:    sys/netinet  tcp_timer.c
>   Log:
>   Setting the TF_ACKNOW flag was redundant in the REXMT timeout because
>   tcp_output() checks for the condition snd_nxt == snd_una.
>   
>   Reviewed by:	davidg, wollman, olah
>   Suggested by:	Richard Stevens

This was not related to T/TCP, just a cosmetic change suggested by
Richard Stevens on comp.protocols.tcp-ip some time ago. 
Unfortunately, this change can cause the m_copydata panic if T/TCP
is used (even if the application uses TCP in the traditional sense)
and some segments are lost.  For the people interested in the
anatomy of this bug, I'll describe the problem in full details.

Andras