> I think that (with %0 being "=m" (sem->waiting)) : "0" (sem->waiting))
> the following code ought to work.
>
> 1: lock; decl %0
> jns 2f /* If result >= 0, success */
> lock; incl %0 /* Went too far; go back */
> jg 1b /* If result > 0, retry */
> return 0;
> 2:
> return 1;
>
> Here, we're transiently letting sem->waiting drop below zero.
> As long as nobody gets confused, that should be fine.
It's probably worth preceding this with the original test, `cmpl $0,%0;
jg 2f', to avoid a thundering herd of locked operations.
Remember to do atomic_inc(&sem->waking) in wake_one_more() too.
Having given your code some thought, it looks ok. The retry loop is
obviously very important.
I can't think of any livelock scenarious either, which is a good sign.
-- Jamie
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