r328113 and affecting SMP systems.
The way the time is set on PowerMacs is racy and relies on all the
CPUs in the system setting a register simultaneously in a rendezvous. A
few-cycle delay can result in out-of-sync times, which can break the
scheduler and result in calls like mtx_sleep() and pause() never timing out
if the thread is migrated while sleeping. r328113 added a call to a no-op
function between the beginning of the rendezvous and setting the time that
was only called on APs and added enough cycles to cause a problematic offset.
For some reason, the fan-management code was the first place this appeared.
Clue from: andreast
Reported by: many
778c8dac96