Re: [PATCH tip/locking/core v8 1/5] locking/qspinlock: Use _acquire/_release versions of cmpxchg & xchg

[Davidlohr Bueso]

On Tue, 20 Oct 2015, Boqun Feng wrote:

> > @@ -93,7 +94,7 @@ static __always_inline void queued_spin_unlock(struct qspinlock *lock)
> >  	/*
> >  	 * smp_mb__before_atomic() in order to guarantee release semantics
> >  	 */
> > -	smp_mb__before_atomic_dec();
> > +	smp_mb__before_atomic();
> >  	atomic_sub(_Q_LOCKED_VAL, &lock->val);
>
> Just be curious, you don't use atomic_sub_release() here on purpose?

atomic_sub() does not imply barriers, so there's no relaxed variants; that's
only for _return() (and such) to the caller.

Thanks,
Davidlohr

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