linux-kernel - Re: [PATCH 2/2] ACPI: HMAT: Fix initiator registration for single-initiator systems

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Message-ID: <b29163f4e39d28c3656b468a52a63b34073cb933.camel@intel.com>
Date:   Wed, 16 Nov 2022 18:02:32 +0000
From:   "Verma, Vishal L" <vishal.l.verma@...el.com>
To:     "kirill@...temov.name" <kirill@...temov.name>
CC:     "Piper, Chris D" <chris.d.piper@...el.com>,
        "rafael@...nel.org" <rafael@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        "Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
        "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "nvdimm@...ts.linux.dev" <nvdimm@...ts.linux.dev>,
        "liushixin2@...wei.com" <liushixin2@...wei.com>
Subject: Re: [PATCH 2/2] ACPI: HMAT: Fix initiator registration for
 single-initiator systems

On Wed, 2022-11-16 at 15:46 +0300, Kirill A. Shutemov wrote:
> On Wed, Nov 16, 2022 at 12:57:36AM -0700, Vishal Verma wrote:
> > In a system with a single initiator node, and one or more memory-only
> > 'target' nodes, the memory-only node(s) would fail to register their
> > initiator node correctly. i.e. in sysfs:
> > 
> >   # ls /sys/devices/system/node/node0/access0/targets/
> >   node0
> > 
> > Where as the correct behavior should be:
> > 
> >   # ls /sys/devices/system/node/node0/access0/targets/
> >   node0 node1
> > 
> > This happened because hmat_register_target_initiators() uses list_sort()
> > to sort the initiator list, but the sort comparision function
> > (initiator_cmp()) is overloaded to also set the node mask's bits.
> > 
> > In a system with a single initiator, the list is singular, and list_sort
> > elides the comparision helper call. Thus the node mask never gets set,
> > and the subsequent search for the best initiator comes up empty.
> > 
> > Add a new helper to sort the initiator list, and handle the singular
> > list corner case by setting the node mask for that explicitly.
> > 
> > Reported-by: Chris Piper <chris.d.piper@...el.com>
> > Cc: <stable@...r.kernel.org>
> > Cc: Rafael J. Wysocki <rafael@...nel.org>
> > Cc: Liu Shixin <liushixin2@...wei.com>
> > Cc: Dan Williams <dan.j.williams@...el.com>
> > Signed-off-by: Vishal Verma <vishal.l.verma@...el.com>
> > ---
> >  drivers/acpi/numa/hmat.c | 32 ++++++++++++++++++++++++++++++--
> >  1 file changed, 30 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/acpi/numa/hmat.c b/drivers/acpi/numa/hmat.c
> > index 144a84f429ed..cd20b0e9cdfa 100644
> > --- a/drivers/acpi/numa/hmat.c
> > +++ b/drivers/acpi/numa/hmat.c
> > @@ -573,6 +573,30 @@ static int initiator_cmp(void *priv, const struct list_head *a,
> >         return ia->processor_pxm - ib->processor_pxm;
> >  }
> >  
> > +static int initiators_to_nodemask(unsigned long *p_nodes)
> > +{
> > +       /*
> > +        * list_sort doesn't call @cmp (initiator_cmp) for 0 or 1 sized lists.
> > +        * For a single-initiator system with other memory-only nodes, this
> > +        * means an empty p_nodes mask, since that is set by initiator_cmp().
> > +        * Special case the singular list, and make sure the node mask gets set
> > +        * appropriately.
> > +        */
> > +       if (list_empty(&initiators))
> > +               return -ENXIO;
> > +
> > +       if (list_is_singular(&initiators)) {
> > +               struct memory_initiator *initiator = list_first_entry(
> > +                       &initiators, struct memory_initiator, node);
> > +
> > +               set_bit(initiator->processor_pxm, p_nodes);
> > +               return 0;
> > +       }
> > +
> > +       list_sort(p_nodes, &initiators, initiator_cmp);
> > +       return 0;
> > +}
> > +
> 
> Hm. I think it indicates that these set_bit()s do not belong to
> initiator_cmp().
> 
> Maybe remove both set_bit() from the compare helper and walk the list
> separately to initialize the node mask? I think it will be easier to
> follow.


Yes - I thuoght about this, but went with the seemingly less intrusive
change. I can send a v2 which separates out the set_bit()s. I agree
that's cleaner and easier to follow than overloading initiator_cmp().