panic: mutex vm object not owned at ../../../vm/vm_page.c:762

I got this upon attempting to burn a CD with cdrecord on my
freshly-updated current machine:

panic: mutex vm object not owned at ../../../vm/vm_page.c:762

syncing disks, buffers remaining... 3842 3842 3842 3842 3842 3842 3842 3842 3842 3842 3842 3842 3842 3842 3842 3842 3842 3842 3842 3842
giving up on 218 buffers
Uptime: 16m51s
Dumping 511 MB
 16 32 48 64 80 96 112 128 144 160 176 192 208 224 240 256 272 288 304 320 336 352 368 384 400 416 432 448 464 480 496
---
Reading symbols from /boot/kernel/nvidia.ko...done.
Loaded symbols for /boot/kernel/nvidia.ko
#0  doadump () at ../../../kern/kern_shutdown.c:240
240             dumping++;
(kgdb) bt
#0  doadump () at ../../../kern/kern_shutdown.c:240
#1  0xc054a32d in boot (howto=256) at ../../../kern/kern_shutdown.c:372
#2  0xc054a6b7 in panic () at ../../../kern/kern_shutdown.c:550
#3  0xc05410cc in _mtx_assert (m=0xc4ea4c24, what=0, file=0xc06f8518 "../../../vm/vm_page.c", line=762)
    at ../../../kern/kern_mutex.c:855
#4  0xc065c03c in vm_page_alloc (object=0xc4ea4c24, pindex=0, req=0) at ../../../vm/vm_page.c:762
#5  0xc064e68b in vm_fault_copy_entry (dst_map=0xc4f527e0, src_map=0xc4d653f0, dst_entry=0xc537fd5c,
    src_entry=0x0) at ../../../vm/vm_fault.c:1167
#6  0xc0654e81 in vm_map_copy_entry (src_map=0xc4d653f0, dst_map=0xc4f527e0, src_entry=0xc537f834,
    dst_entry=0xc537fd5c) at ../../../vm/vm_map.c:2379
#7  0xc06551c6 in vmspace_fork (vm1=0xc4d653f0) at ../../../vm/vm_map.c:2494
#8  0xc064fcce in vm_forkproc (td=0xc4ebe130, p2=0xc53855ac, td2=0xc4ebeab0, flags=20)
    at ../../../vm/vm_glue.c:624
#9  0xc05353f5 in fork1 (td=0xc4ebe130, flags=20, pages=0, procp=0xd9d38cd8) at ../../../kern/kern_fork.c:654
#10 0xc053441b in fork (td=0xc4ebe130, uap=0xd9d38d10) at ../../../kern/kern_fork.c:102
#11 0xc06a4d93 in syscall (frame=
      {tf_fs = 47, tf_es = 47, tf_ds = 47, tf_edi = 4096, tf_esi = 65536, tf_ebp = -1077948008, tf_isp = -640447116, tf_ebx = 64, tf_edx = 1307, tf_ecx = 672806144, tf_eax = 2, tf_trapno = 0, tf_err = 2, tf_eip = 672202079, tf_cs = 31, tf_eflags = 582, tf_esp = -1077948052, tf_ss = 47}) at ../../../i386/i386/trap.c:1006
#12 0xc069505d in Xint0x80_syscall () at {standard input}:144
---Can't read userspace from dump, or kernel process---
(kgdb)

The annoying thing was that something apparently overwrote the
partition table on the disk holding the swap partition - I had to
recreate it by hand before I could bring the system back up, although
it then came back up without further problems.

Kris