Re: [PATCH 04/21] Generic percpu refcounting

[Oleg Nesterov]

On 05/14, Tejun Heo wrote:
>
> > +int percpu_ref_tryget(struct percpu_ref *ref)
> > +{
> > +	int ret = 1;
> > +
> > +	preempt_disable();
> > +
> > +	if (!percpu_ref_dead(ref))
> > +		percpu_ref_get(ref);
> > +	else
> > +		ret = 0;
> > +
> > +	preempt_enable();
> > +
> > +	return ret;
> > +}
...
> BTW, why is this
> function necessary?  What's the use case?

Yes, I was wondering too.

And please note that this code _looks_ wrong, percpu_ref_get() still
can increment ref->count.

Hmm. Just noticed this comment above percpu_ref_kill()

	* The caller must issue a synchronize_rcu()/call_rcu() before calling
	* percpu_ref_put() to drop the initial ref.

Really?

Oleg.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/