Interesting panic in current

[Doug Rabson]

I just had this panic on a current box. This machine is running 
post-gcc-3.4 current with PREEMPTION disabled. The hardware is a Tyan 
Tiger MP motherboard with two Athlon 1900 MP processors. I was running 
an SMP kernel.



Fatal trap 12: page fault while in kernel mode
cpuid = 0; apic id = 01
fault virtual address   = 0xbfca0704
fault code              = supervisor read, page not present
instruction pointer     = 0x8:0xc065d145
stack pointer           = 0x10:0xd3adbc78
frame pointer           = 0x10:0xd3adbc84
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         = 91207 (sh)
[thread 100071]
Stopped at      pmap_remove_pages+0xa9: movl    PTmap(%eax),%ecx
db> tr
pmap_remove_pages(c2e63d30,0,bfc00000) at pmap_remove_pages+0xa9
exit1(c1fa16e0,0,d3adbd40,c065fdcb,c1fa16e0) at exit1+0x4dd
exit1(c1fa16e0,d3adbd14,1,46,296) at exit1
syscall(2f,2f,2f,bfbfe66c,bfbfe650) at syscall+0x217
Xint0x80_syscall() at Xint0x80_syscall+0x1f
--- syscall (1, FreeBSD ELF32, sys_exit), eip = 0x2813233f, esp = 
0xbfbfe50c, ebp = 0xbfbfe588 ---
db> p $eax
   a0704
db> p/x
   a0704
db> x/x PTmap
PTmap:  *** error reading from address bfc00000 ***
db>
PTmap:  *** error reading from address bfc00000 ***
db> x/x PTmap + 0xa0704
0xbfca0704:     *** error reading from address bfca0704 ***
db> c