Re: [BETA7-panic] sodealloc(): so_count 1

On Fri, 15 Oct 2004, Marc UBM Bocklet wrote:

> > Sounds good.  I know that the problem Brian identified is a real race
> > and a potential source of precisely the panic you were seeing.  One
> > reason I was interested in getting access to a dump from the panic,
> > though, was to(if possible) confirm that it was *the* race causing the
> > problem.  It's a very likely candidate, but it would be good to know
> > if we should be looking for another related race.  If the code now in
> > HEAD fixes it for you, please let me know (or if not, also :-).  If it
> > doesn't, the core would be very helpful.
> 
> Ok, bad news first: 
> 
> I just got exactly the same panic with Brian's
> tcp_accept_race_crash.patch applied. 
> 
> Debug output is attached, but it looks just like the last time. 
> 
> The good news: 
> 
> I got a coredump that I can poke. :-) 
> 
> So now I just need to know what info to extract from the dump :-) 

It would be interesting to have you try with the current head of RELENG_5,
which now includes my fix, which is a little different from Brian's fix in
the sense that it tries to rewrite things less (since that code is very
sensitive to change).

Regarding the dump -- wonderful.  Here's what I'd like you to do.  In one
of the sofree/sodealloc frames, I'd like to see the contents of *so, to
see what state the socket is in.  If you move up a few frames to
in_pcbdetach(), the contents of *inp would be very useful, and up another
frame or so to the tcp_close() frame, *tp.  I don't know how fmiliar you
are with our kernel debugging suite, but if you're not the documentation
in the handbook is fairly decent.  The one caveat I'd give is that that
documentation might still reference "gdb -k" instead of "kgdb" to work
with the core dump.

Thanks for your help on this one -- I'm still unable to reproduce the
problem in my testbeds, so having someone who's willing to keep following
through on the bug is really invaluable!

Thanks,

Robert N M Watson             FreeBSD Core Team, TrustedBSD Projects
robert_at_fledge.watson.org      Principal Research Scientist, McAfee Research