NOTE: I think there's races with timer_spkr_{acquire,release} since there's no interlock in those routines, despite there being a spin lock to protect the clock. Current other users appear to use no extra locking protocol, though they themselves appear to be at least attempting to make sure that only a single thread calls these routines. I suspect the right answer is to update these routines to take/release the clock spin lock since they are short and to the point, but that's beyond the scope of this commit.