linux-kernel - Re: [PATCH] hmat: Register attributes for memory hot add

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Date:   Thu, 11 Apr 2019 09:00:57 -0600
From:   Keith Busch <keith.busch@...el.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Brice Goglin <Brice.Goglin@...ia.fr>
Subject: Re: [PATCH] hmat: Register attributes for memory hot add

On Thu, Apr 11, 2019 at 04:42:45PM +0200, Rafael J. Wysocki wrote:
> On Tue, Apr 9, 2019 at 11:42 PM Keith Busch <keith.busch@...el.com> wrote:
> > -static __init void hmat_register_targets(void)
> > +static void hmat_register_targets(void)
> >  {
> >         struct memory_target *target;
> >
> >         list_for_each_entry(target, &targets, node) {
> > +               if (!node_online(pxm_to_node(target->memory_pxm)))
> > +                       continue;
> > +
> >                 hmat_register_target_initiators(target);
> >                 hmat_register_target_perf(target);
> > +               target->registered = true;
> >         }
> >  }
> >
> > +static int hmat_callback(struct notifier_block *self,
> > +                        unsigned long action, void *arg)
> > +{
> > +       struct memory_notify *mnb = arg;
> > +       int pxm, nid = mnb->status_change_nid;
> > +       struct memory_target *target;
> > +
> > +       if (nid == NUMA_NO_NODE || action != MEM_ONLINE)
> > +               return NOTIFY_OK;
> > +
> > +       pxm = node_to_pxm(nid);
> > +       target = find_mem_target(pxm);
> > +       if (!target || target->registered)
> > +               return NOTIFY_OK;
> > +
> > +       hmat_register_target_initiators(target);
> > +       hmat_register_target_perf(target);
> > +       target->registered = true;
> > +
> > +       return NOTIFY_OK;
> > +}
> 
> This appears to assume that there will never be any races between the
> two functions above.
> 
> It this guaranteed to be the case?

The hmat_init() will call this directly before registering the memory
notifier callback, so those two paths should be 'ok'.

I may have assumed memory notification callbacks were single threaded,
but after taking a quick look, I think I do need additional locking for
this to be safe. I'll get that fixed up, thanks for the catch.