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

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Date:   Wed, 16 Nov 2022 15:46:34 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Vishal Verma <vishal.l.verma@...el.com>
Cc:     linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
        nvdimm@...ts.linux.dev,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Dan Williams <dan.j.williams@...el.com>, liushixin2@...wei.com,
        Chris Piper <chris.d.piper@...el.com>, stable@...r.kernel.org,
        "Rafael J . Wysocki" <rafael@...nel.org>
Subject: Re: [PATCH 2/2] ACPI: HMAT: Fix initiator registration for
 single-initiator systems

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.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov