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.
