riz@boogers.sf.ca.us said:
> My suspicion is that I've removed something from the kernel config

I don't see anything obvious - my only recommendation would be
to just add DIAGNOSTIC to your custom configuration.
(It might be that an FPU context is saved for a process which
doesn't exist anymore. There are some diagnostic assertions
which could catch some - not all - of these cases.)
And it might be helpful to provide a stacktrace of the other CPU
("machine cpu X").

best regards
Matthias