On Tue, 24 Sep 2013 18:03:59 +0200
Oleg Nesterov <oleg@xxxxxxxxxx> wrote:
> On 09/24, Peter Zijlstra wrote:
> >
> > +static inline void get_online_cpus(void)
> > +{
> > + might_sleep();
> > +
> > + if (current->cpuhp_ref++) {
> > + barrier();
> > + return;
>
> I don't undestand this barrier()... we are going to return if we already
> hold the lock, do we really need it?
I'm confused too. Unless gcc moves this after the release, but the
release uses preempt_disable() which is its own barrier.
If anything, it requires a comment.
-- Steve
>
> The same for put_online_cpus().
>
> > +void __get_online_cpus(void)
> > {
> > - if (cpu_hotplug.active_writer == current)
> > + if (cpuhp_writer_task == current)
> > return;
>
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