On Thu, Jun 19, 2014 at 09:31:04AM -0400, Tejun Heo wrote:
> On Thu, Jun 19, 2014 at 11:01:26AM +0800, Lai Jiangshan wrote:
> > > + /*
> > > + * Restore per-cpu operation. smp_store_release() is paired with
> > > + * smp_load_acquire() in __pcpu_ref_alive() and guarantees that the
> >
> > s/smp_load_acquire()/smp_read_barrier_depends()/
>
> Will update.
>
> > s/smp_store_release()/smp_mb()/ if you accept my next comment.
> >
> > > + * zeroing is visible to all percpu accesses which can see the
> > > + * following PCPU_REF_DEAD clearing.
> > > + */
> > > + for_each_possible_cpu(cpu)
> > > + *per_cpu_ptr(pcpu_count, cpu) = 0;
> > > +
> > > + smp_store_release(&ref->pcpu_count_ptr,
> > > + ref->pcpu_count_ptr & ~PCPU_REF_DEAD);
> >
> > I think it would be better if smp_mb() is used.
>
> smp_wmb() would be better here. We don't need the reader side.
>
> > it is documented that smp_read_barrier_depends() and smp_mb() are paired.
> > Not smp_read_barrier_depends() and smp_store_release().
Well, sounds like the documentation needs an update, then. ;-)
For example, current rcu_assign_pointer() is a wrapper around
smp_store_release().
> I don't know. I thought about doing that but the RCU accessors are
> pairing store_release with read_barrier_depends, so I don't think the
> particular paring is problematic and store_release is better at
> documenting what's being barriered.
Which Tejun noted as well.
Thanx, Paul
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