Re: [PATCH] locking/percpu_rwsem: Rewrite to not use rwsem

Boqun Feng
2019-08-05T14:58:25Z

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On Mon, Aug 05, 2019 at 10:43:18PM +0800, Boqun Feng wrote:
> On Mon, Aug 05, 2019 at 04:02:41PM +0200, Peter Zijlstra wrote:
> [...]
> >
> > static inline void percpu_up_read(struct percpu_rw_semaphore *sem)
> > {
> > + rwsem_release(&sem->dep_map, 1, _RET_IP_);
> > +
> > preempt_disable();
> > /*
> > * Same as in percpu_down_read().
> > */
> > - if (likely(rcu_sync_is_idle(&sem->rss)))
> > + if (likely(rcu_sync_is_idle(&sem->rss))) {
> > __this_cpu_dec(*sem->read_count);
> > - else
> > - __percpu_up_read(sem); /* Unconditional memory barrier */
> > - preempt_enable();
> > + preempt_enable();
> > + return;
> > + }
> >
> > - rwsem_release(&sem->rw_sem.dep_map, 1, _RET_IP_);
>
> Missing a preempt_enable() here?
>

Ah.. you modified the semantics of __percpu_up_read() to imply a
preempt_enable(), sorry for the noise...

Regards,
Boqun

> Regards,
> Boqun
>
> > + __percpu_up_read(sem); /* Unconditional memory barrier */
> > }
> >
> [...]

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