Re: [PATCH-tip 04/22] locking/rwsem: Remove arch specific rwsem files

[Peter Zijlstra]

On Thu, Feb 07, 2019 at 08:36:56PM +0100, Peter Zijlstra wrote:
> On Thu, Feb 07, 2019 at 02:07:08PM -0500, Waiman Long wrote:
> 
> > +static inline int __down_read_trylock(struct rw_semaphore *sem)
> > +{
> > +	long tmp;
> > +
> > +	while ((tmp = atomic_long_read(&sem->count)) >= 0) {
> > +		if (tmp == atomic_long_cmpxchg_acquire(&sem->count, tmp,
> > +				   tmp + RWSEM_ACTIVE_READ_BIAS)) {
> > +			return 1;
> > +		}
> > +	}
> 
> Nah, you're supposed to write that like:
> 
> 	for (;;) {
> 		val = atomic_long_cond_read_relaxed(&sem->count, VAL < 0);
> 		if (atomic_long_try_cmpxchg_acquire(&sem->count, &val,
> 						    val + RWSEM_ACTIVE_READ_BIAS))
> 			break;
> 	}

N/m that's not in fact the same...

> > +	return 0;
> > +}
> 
> 
> Anyway, yuck, you're keeping all that BIAS nonsense :/ I was so hoping
> for a rwsem implementation without that impenetrable crap.