>  > (gdb) print *mbp
>  try "print *bp" instead.
  
(gdb) print *bp
can not access 0x800, invalid translation (invalid PTE)
can not access 0x800, invalid translation (invalid PTE)
Cannot access memory at address 0x800

>  what's your underlying disk driver?

viaide.

Also, I've found that gmplayer (and not mplayer, oddly enough) will
repeatably cause the panic, so it's not I/O load related.

I can upload the corefile/netbsd.gdb to mail.netbsd.org if you like.