Fix a preemption race.  I was reenabling interrupts in the fast system call handler before it was safe.  It was possible for to lose context and for something else to clobber the PCPU scratch variable.  This moves the interrupt enable *way* too late, but its better safe than sorry for the moment.
Fix a preemption race.  I was reenabling interrupts in the fast system
call handler before it was safe.  It was possible for to lose context
and for something else to clobber the PCPU scratch variable.  This
moves the interrupt enable *way* too late, but its better safe than
sorry for the moment.

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