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Date:      Wed, 3 Jan 2001 16:11:31 +1030
From:      Greg Lehey <grog@lemis.com>
To:        Manfred Antar <null@pozo.com>
Cc:        FreeBSD SMP list <FreeBSD-smp@FreeBSD.org>
Subject:   Re: Fatal trap while printing under SMP
Message-ID:  <20010103161131.K4336@wantadilla.lemis.com>
In-Reply-To: <5.0.2.1.2.20010102210933.046d3d70@pozo.com>; from null@pozo.com on Tue, Jan 02, 2001 at 09:17:24PM -0800
References:  <5.0.2.1.2.20010102204401.00b13e88@pozo.com> <5.0.2.1.2.20010102204401.00b13e88@pozo.com> <20010103153459.J4336@wantadilla.lemis.com> <5.0.2.1.2.20010102210933.046d3d70@pozo.com>

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On Tuesday,  2 January 2001 at 21:17:24 -0800, Manfred Antar wrote:
> At 03:34 PM 1/3/2001 +1030, you wrote:
>> On Tuesday,  2 January 2001 at 20:49:04 -0800, Manfred Antar wrote:
>>> When trying to print using a current SMP kernel, I get the following:
>>>
>>> Fatal trap 12: page fault while in kernel mode
>>> cpuid = 1; lapic.id = 0c000000
>>> fault virtual address   = 0xe1810412
>>> fault code              = supervisor write, page not present
>>> instruction pointer     = 0x8:0xcb0a7977
>>> stack pointer           = 0x10:0xcb08cf84
>>> frame pointer           = 0x10:0xcb08cf9c
>>> code segment            = base 0x0, limit 0xfffff, type 0x1b
>>>                         = DPL 0, pres 1, def32 1, gran 1
>>> processor eflags        = interrupt enabled, resume, IOPL = 0
>>> current process         = 30652 (irq7: lpt0)
>>> trap number             = 12
>>> panic: page fault
>>> cpuid = 1; lapic.id = 0c000000
>>> boot() called on cpu#1
>>
>> We really need more information than this.  Can you get a dump, or at
>> least a stack trace?
>
> The machine freezes solid.

You mean you can't even press Enter to get it to reboot?  Bad news.

> I have to do a reset to get it going again.  I'm running it headless
> off a serial port. I could hook a monitor and a keyboard to it and
> try to get to the debugger but I have a feeling its going to be
> wedged.  How do i get a stack trace from debugger ?

If you can get into the debugger, the ddb command is 't'.  If you're
doing remote serial debug with gdb, it's 'bt'.

Unfortunately, it's not likely to help you much here.  The IP value
(cb0a7977) is almost certainly wrong.  In other words, the real
problem has already been lost.  Under more normal circumstances, you
could try this:

  # nm /boot/kernel/kernel | sort | less

Then look for the fault IP address.  Don't forget to remove the 0x at
the beginning.  But I strongly doubt you'll find anything.

Greg
--
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