Ok, I'm close to tracking this one down. It's a critical section
mismatch somewhere. A critical section gets entered and never gets
released, the user process then runs in a critical section which as
you can imagine can lead to, oh, things like interrupts not working
any more, and infinite loops locking up the box as well.
I am adding INVARIANTS code to panic if the critical section count
becomes mismatched and hopefully I'll track down the current mismatch
soon.
-Matt
