RELENG_6 regression: panic: vm_fault on nofault entry, addr: c8000000

[Gavin Atkinson]

On Wed, 2008-05-14 at 17:32 +0200, Ulrich Spoerlein wrote:
> Hi,
> 
> there's a regression going from 6.2 to 6.3, where it will panic upon
> booting the kernel within vm_fault. This problem has been discussed
> before, but I'm seeing it reliably on a RELENG_6 checkout from 5th of
> May.
> 
> It affects multiple (but identical) systems, here's an verbose boot
> leading to the panic. Please note that 6.2 was running fine on these
> machines, they also boot "normally" if I disable ACPI (but this is not
> really an option).

[snip dmesg output]

> What to do?

If you don't get any suggestions from people as to what it may be, and
you have a system you can afford to reboot a few times, the easiest
thing to do is to take the system back to 6.2, and then update your
source to a date midway between 6.2 and 6.3 and see if that crashes.
Use this in your supfile:

*default tag=RELENG_6
*default date=2007.07.01.00.00.00

(For reference, 6.2 was released on 2007.01.15, with 6.3 on 2008.01.18)

>From then, go half way again either forwards or backwards, to narrow
down the window when the problem was introduced - with only eight kernel
recompiles you should be able to narrow it down to a one-day window, and
looking at the spec of the machine you should be able to do that in a
morning :).  Once you've got it down to a window of a couple of days or
less, give csup the "-L 2" option, and it'll give you a list of files
changed between dates.  

Obviously this is dependant on you being able to take one of the
affected machines down for a few hours, but if you can, this may well be
the quickest way of establishing when the problem was introduced.

Out of interest, what type of hardware is this?

Gavin