> #define mutex_init(m,s)		(m).spl=(s)
> 
> #define mutex_enter(m)		(m).oldspl = splraise((m).spl)
> #define mutex_exit(m)		splx((m).oldspl)
> 
> You will need to replace all the spl stuff with this.  Then you can
> start worrying about isolating critical sections that are not currently
> protected due to our single-threaded kernel design.  

The problem with this implementation is that `oldspl' needs to be
stuffed in a temporary variable with a scope covering the lock/unlock,
not in a global variable..

i.e., it's currently legal to do:

	x = splfoo();
	y = splfoo();

	splx(y);
	splx(x);

Nesting your mutex_enter/mutex_exit, on the other hand, leave things
locked on exit...