cpu_fork() mistakenly created processes forked by proc0, including
kthreads, in splhigh condition, because [1] proc0's PCB was zero
cleared during initialization, and [2] value 0 in status register
field made processes to have splhigh condition when CPU tick was
assigned for them. This mostly doesn't matter as forked processes
dive immediately into user mode through proc_trampoline code path,
however, kthreads never do that and remain in splhigh.
Reported by Ethan Solomita <ethan@geocast.com>.
nisimura