From: Ingo Molnar <mingo@elte.hu>,

Voyager is getting odd deadlocks due to the taking of xtime_lock() in
sched_clock()->get_jiffies_64().

I had this patch queued up to fix a different deadlock, which occurs when we
relax the requirement that TSC's be synchronised across CPUs.  But it will
fix James' deadlock too.