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Date:   Wed, 16 Nov 2022 23:44:51 +0300
From:   "kirill@shutemov.name" <kirill@shutemov.name>
To:     "Verma, Vishal L" <vishal.l.verma@intel.com>
Cc:     "Piper, Chris D" <chris.d.piper@intel.com>,
        "rafael@kernel.org" <rafael@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "Williams, Dan J" <dan.j.williams@intel.com>,
        "Wysocki, Rafael J" <rafael.j.wysocki@intel.com>,
        "linux-acpi@vger.kernel.org" <linux-acpi@vger.kernel.org>,
        "stable@vger.kernel.org" <stable@vger.kernel.org>,
        "nvdimm@lists.linux.dev" <nvdimm@lists.linux.dev>,
        "liushixin2@huawei.com" <liushixin2@huawei.com>
Subject: Re: [PATCH 2/2] ACPI: HMAT: Fix initiator registration for
 single-initiator systems
Message-ID: <20221116204451.rmh6lq7vilajg7ss@box.shutemov.name>
References: <20221116075736.1909690-1-vishal.l.verma@intel.com>
 <20221116075736.1909690-3-vishal.l.verma@intel.com>
 <20221116124634.nlvnsirdnlafdfeh@box.shutemov.name>
 <b29163f4e39d28c3656b468a52a63b34073cb933.camel@intel.com>
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On Wed, Nov 16, 2022 at 06:02:32PM +0000, Verma, Vishal L wrote:
> 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().

Yes, please make v2.

With current implementation set_bit() can be called multiple times on the
same initiator, depending on placement of the initiator in the list.
It is totally wrong place.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov