Re: Panic "Fatal trap 18: integer divide fault while in kernel mode"

2009/5/1 Jung-uk Kim <jkim_at_freebsd.org>:
> On Thursday 30 April 2009 04:25 pm, pluknet wrote:
>> 2009/4/30 Jung-uk Kim <jkim_at_freebsd.org>:
>> > On Thursday 30 April 2009 12:37 pm, pluknet wrote:
>> >> 2009/4/30 Andriy Gapon <avg_at_icyb.net.ua>:
>> >> > on 30/04/2009 18:58 David Wolfskill said the following:
>> >> >> On Thu, Apr 30, 2009 at 06:35:32PM +0300, Andriy Gapon wrote:
>> >> >>> on 30/04/2009 18:18 David Wolfskill said the following:
>> >> >>>> On Wed, Apr 29, 2009 at 09:16:26AM -0700, David Wolfskill
>> >
>> > wrote:
>> >> >>>>> Is there anything of use I might get from DDB?
>> >> >>>>
>> >> >>>> I can still poke around there for a bit, if that would be
>> >> >>>> useful.
>> >> >>>
>> >> >>> In general the stack trace[*] should be provided at the very
>> >> >>> least, otherwise people have hard figuring out where the
>> >> >>> problem occurred, so right people may just not notice a
>> >> >>> report.
>> >> >>
>> >> >> Sorry; it happened so quickly, I wasn't at all certain there
>> >> >> would be enough to show:
>> >> >>
>> >> >> db> bt
>> >> >> Tracing pid 0 tid 100000 td 0xc0d43610
>> >> >> cpu_topo(2,c1420d34,c081ff07,c1420d58,c0820042,...) at
>> >> >> cpu_topo+0x43 smp_topo(c0804378,2,c4145a5c,fffffff,0,...) at
>> >> >> smp_topo+0x10b
>> >> >> sched_setup(0,141ec00,141ec00,141e000,1425000,...) at
>> >> >> sched_setup+0x1a mi_startup() at mi_startup+0x96
>> >> >> begin() at begin+0x2c
>> >> >
>> >> > My guess is that (cpu_cores * cpu_logical) somehow equals to
>> >> > zero.
>> >>
>> >> That was masked earlier by  additional checks on zero,
>> >> and now that routine moved to the separate function
>> >> (and to separate call path from subr_smp.c:mp_start()
>> >> which seems not to be called).
>> >>
>> >> > Have you by a chance saved this crash dump?
>> >> > I think that t would be interesting to look at it in kgdb.
>> >
>> > Please try the attached patch.
>> >
>> > Jung-uk Kim
>>
>> The strange thing is why cpu_mp_start() is called at all in case
>> when there is only one CPU in system. It should early return in
>> mp_start(). (I saw two reports and both of them were UP systems).
>
> I don't think cpu_mp_start() is the culprit.
Actually you are right. I was wrong and cpu_mp_start() is not called here on UP.

> When SMP kernel is used
> on UP system, scheduler still tries to probe topology although it
> should be simply smp_topo_none() instead of calling MD cpu_topo().
> In fact, I had a simple band-aid in cpu_topo() in my local tree to
> shut up annoying:
>
>        WARNING: Non-uniform processors.
>        WARNING: Using suboptimal topology.
>
> messages when SMP is forced off or a core is disabled on multi-core
> systems, etc.  It wasn't critical before but it is now,
> unfortunately.
>
> Jung-uk Kim
>

I decided to go another way. Before last changes in mp_machdep.c
cpu_topo() included
previously that piece of code which now is in topo_probe().

What if just return that part back to cpu_topo() ?

David, can you thy this? It works for me now at least.

$ diff -urp sys/amd64/amd64/mp_machdep.c.orig sys/amd64/amd64/mp_machdep.c
--- sys/amd64/amd64/mp_machdep.c.orig   2009-05-01 00:59:55.000000000 +0400
+++ sys/amd64/amd64/mp_machdep.c        2009-05-01 01:00:20.000000000 +0400
_at__at_ -309,6 +309,8 _at__at_ cpu_topo(void)
 {
        int cg_flags;

+       topo_probe();
+
        /*
         * Determine whether any threading flags are
         * necessry.
$ diff -urp sys/i386/i386/mp_machdep.c.orig sys/i386/i386/mp_machdep.c
--- sys/i386/i386/mp_machdep.c.orig     2009-05-01 01:01:53.000000000 +0400
+++ sys/i386/i386/mp_machdep.c  2009-05-01 01:01:41.000000000 +0400
_at__at_ -362,6 +362,8 _at__at_ cpu_topo(void)
 {
        int cg_flags;

+       topo_probe();
+
        /*
         * Determine whether any threading flags are
         * necessry.


-- 
wbr,
pluknet