Sometimes my workstation just feel like crashing:

main# gdb -k kernel.debug vmcore.0
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details. This GDB was configured as "i386-unknown-freebsd"...
panic: privileged instruction fault
panic messages:
---
Fatal trap 1: privileged instruction fault while in kernel mode
instruction pointer     = 0x8:0xc04b1be0
stack pointer           = 0x10:0xd84d7b34
frame pointer           = 0x10:0xd84d7b5c
code segment            = base rx0, limit 0xfffff, type 0x1b
                        = DPL 0, pres 1, def32 1, gran 1
processor eflags        = interrupt enabled, resume, IOPL = 0
current process         = 603 (mixer_applet2)
trap number             = 1
panic: privileged instruction fault
 
syncing disks, buffers remaining... 3034 3034 3034 3034 3034 3034 3034
3034 3034 3034 3034 3034 3034 3034 3034 3034 3034 3034 3034 3034 giving
up on 1905 buffers Uptime: 3h33m37s
Dumping 383 MB
 16 32 48 64 80 96 112 128 144 160 176 192 208 224 240 256 272 288 304
320 336 352 368---
 
Reading symbols from
/usr/obj/usr/src/sys/MAIN/modules/usr/src/sys/modules/acpi/acpi.ko.debu
g...done. Loaded symbols for
/usr/obj/usr/src/sys/MAIN/modules/usr/src/sys/modules/acpi/acpi.ko.debug
Reading symbols from
/usr/obj/usr/src/sys/MAIN/modules/usr/src/sys/modules/linux/linux.ko.de
bug...done. Loaded symbols for
/usr/obj/usr/src/sys/MAIN/modules/usr/src/sys/modules/linux/linux.ko.de
bug#0  doadump () at /usr/src/sys/kern/kern_shutdown.c:240
240             dumping++;
(kgdb) where
#0  doadump () at /usr/src/sys/kern/kern_shutdown.c:240
#1  0xc0516002 in boot (howto=256) at
/usr/src/sys/kern/kern_shutdown.c:372
#2  0xc0516337 in panic () at
/usr/src/sys/kern/kern_shutdown.c:550
#3  0xc06207e6 in trap_fatal
(frame=0xd84d7af4, eva=0)    at /usr/src/sys/i386/i386/trap.c:821
#4  0xc0620252 in trap (frame=
      {tf_fs = -1068367848, tf_es = -1013252080, tf_ds = -1050738672,
tf_edi = -1066860640, tf_esi = -666010752, tf_ebp = -666010788, tf_isp =
-666010848, tf_ebx = -1008446448, tf_edx = -666010752, tf_ecx = 40,
tf_eax = -1066679120, tf_trapno = 1, tf_err = 0, tf_eip = -1068819488,
tf_cs = 8, tf_eflags = 2163270, tf_esp = -1068636644, tf_ss =
-1066679120}) at /usr/src/sys/i386/i386/trap.c:618
#5  0xc0611ec8 in
calltrap () at {standard input}:94
#6  0xc04dddb8 in spec_vnoperate
(ap=0x0)    at /usr/src/sys/fs/specfs/spec_vnops.c:122
#7  0xc0576ca1 in vn_ioctl (fp=0xc3faa044, com=3228106656,
data=0xd84d7c58,    active_cred=0xd84d7b80, td=0xc39b3640) at
vnode_if.h:503
#8  0xc053aff1 in ioctl (td=0xc39b3640, uap=0xd84d7d14)
    at /usr/src/sys/sys/file.h:261
#9  0xc0620b00 in syscall (frame=
      {tf_fs = 47, tf_es = 47, tf_ds = 134545455, tf_edi = 36, tf_esi =
0, tf_ebp = -1077942824, tf_isp = -666010252, tf_ebx = 673121972, tf_edx
= 36, tf_ecx = 135254336, tf_eax = 54, tf_trapno = 22, tf_err = 2,
tf_eip = 684891311, tf_cs = 31, tf_eflags = 2099863, tf_esp =
-1077942868, tf_ss = 47})---Type <return> to continue, or q <return> to
quit---q at /usr/src/sys/i386Quit
(kgdb) up 5
#5  0xc0611ec8 in calltrap () at {standard input}:94
94      {standard input}: No such file or directory.
        in {standard input}
Current language:  auto; currently asm
(kgdb) up 6
#6  0xc04dddb8 in spec_vnoperate (ap=0x0)
    at /usr/src/sys/fs/specfs/spec_vnops.c:122
122             return (VOCALL(spec_vnodeop_p, ap->a_desc->vdesc_offset,
ap));
(kgdb) p spec_vnodeop_p
$3 = (vop_t **) 0xc3704000
(kgdb) p *spec_vnodeop_p
$4 = (vop_t *) 0xc0561c10 <vop_eopnotsupp>
(kgdb) p ap
$5 = (struct vop_generic_args *) 0x0
(kgdb) p ap->a_desc->vdesc_offset
---Can't read userspace from dump, or kernel process---

Fix: 

Wish I had one, but no....
How-To-Repeat: 

Don't think you can