Is there anything useful I could do with the coredump to help anyone
   figure out what's wrong?  Does NetBSD's kernel postmortem gdb have any
   way to look at things like non-curproc process's kernel stack?

pk told me this a long time ago:
   
   I suggest using `gdb -k /netbsd /dev/mem' in this case. Use `ps -Opaddr' to
   find the process' proc structure address, prefix this with `0xf8' (probably)
   and use this as an argument to gdb's `proc' command. This will set gdb's
   process context to the desired process. `bt' should then give you the process'
   kernel stack.
   
hope it helps,

.mrg.