Reproduceable kernel panic on boot

[Cliff L. Biffle]

Using sources updated a couple hours ago, I can't boot kernels.  There's a 
panic at each boot, just after 'start_init: trying /sbin/init'.  The panic is 
generally in swapper, but sometimes does not list a current process.  No dump 
is generated.

This has been happening to me all day, starting with sources from yesterday.

The most distressing part is that with the most recent sources, the kernel 
install process did -not- back up my old kernel in kernel.old, so I have no 
working kernel anywhere on the machine.  I suppose I should probably backup 
/boot/kernel manually rather than relying on the build process.

The panic messages are as follows.

---begin---
Fatal trap 12: page fault while in kernel mode
fault virtual address   = 0x0
fault code              = supervisor write, page not present
instruction pointer     = 0x8:0xc1c1bd75
stack pointer           = 0x10:0xc998e8b4
frame pointer           = 0x10:0x0
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         = 1 (swapper)
trap number             = 12
panic: page fault

syncing disks, buffers remaining...
---end---

I'd like to attach my kernel configuration, but have no working kernel on the 
machine.  Yay.  It's basically GENERIC configured for I586 with at least the 
following added:
options GEOM_AES, GEOM_BDE, GEOM_BSD, GEOM_GPT, GEOM_MBR, GEOM_VOL
options PSM_RESETAFTERSUSPEND
options CPU_SUSP_HLT, CPU_WT_ALLOC, NO_F00F_HACK, NO_MEMORY_HOLE

The machine is a K6-2; I've uncommented the CFLAGS and COPTFLAGS in make.conf 
but left them unchanged, and set cputype to k6-2.

While I am using ccache, I've cleared and reset my caches and the problem 
still occurs.

Please, help!  Now I get to see if I remember how to revert the entire tree to 
a couple days ago. :-)

-Cliff L. Biffle