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    SubjectRe: [PATCH 2/2] ACPI: HMAT: Fix initiator registration for single-initiator systems
    Date
    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@intel.com>
    > > Cc: <stable@vger.kernel.org>
    > > Cc: Rafael J. Wysocki <rafael@kernel.org>
    > > Cc: Liu Shixin <liushixin2@huawei.com>
    > > Cc: Dan Williams <dan.j.williams@intel.com>
    > > Signed-off-by: Vishal Verma <vishal.l.verma@intel.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().
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