linux-kernel - Re: [PATCH v2 2/2] ACPI: HMAT: Fix initiator registration for single-initiator systems

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Date:   Thu, 17 Nov 2022 17:20:01 +0100
From:   "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
To:     Vishal Verma <vishal.l.verma@...el.com>,
        <linux-kernel@...r.kernel.org>,
        Chris Piper <chris.d.piper@...el.com>,
        <nvdimm@...ts.linux.dev>, <linux-acpi@...r.kernel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Liu Shixin <liushixin2@...wei.com>, <stable@...r.kernel.org>
Subject: Re: [PATCH v2 2/2] ACPI: HMAT: Fix initiator registration for
 single-initiator systems

On 11/17/2022 12:37 AM, 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 consume the sorted initiator list, and generate the
> nodemask, decoupling it from the overloaded initiator_cmp() comparision
> callback. This prevents the singular list corner case naturally, and
> makes the code easier to follow as well.
>
> 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>
> Cc: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Reported-by: Chris Piper <chris.d.piper@...el.com>
> Signed-off-by: Vishal Verma <vishal.l.verma@...el.com>

Acked-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>


> ---
>   drivers/acpi/numa/hmat.c | 26 ++++++++++++++++++++------
>   1 file changed, 20 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/acpi/numa/hmat.c b/drivers/acpi/numa/hmat.c
> index 144a84f429ed..6cceca64a6bc 100644
> --- a/drivers/acpi/numa/hmat.c
> +++ b/drivers/acpi/numa/hmat.c
> @@ -562,17 +562,26 @@ static int initiator_cmp(void *priv, const struct list_head *a,
>   {
>   	struct memory_initiator *ia;
>   	struct memory_initiator *ib;
> -	unsigned long *p_nodes = priv;
>   
>   	ia = list_entry(a, struct memory_initiator, node);
>   	ib = list_entry(b, struct memory_initiator, node);
>   
> -	set_bit(ia->processor_pxm, p_nodes);
> -	set_bit(ib->processor_pxm, p_nodes);
> -
>   	return ia->processor_pxm - ib->processor_pxm;
>   }
>   
> +static int initiators_to_nodemask(unsigned long *p_nodes)
> +{
> +	struct memory_initiator *initiator;
> +
> +	if (list_empty(&initiators))
> +		return -ENXIO;
> +
> +	list_for_each_entry(initiator, &initiators, node)
> +		set_bit(initiator->processor_pxm, p_nodes);
> +
> +	return 0;
> +}
> +
>   static void hmat_register_target_initiators(struct memory_target *target)
>   {
>   	static DECLARE_BITMAP(p_nodes, MAX_NUMNODES);
> @@ -609,7 +618,10 @@ static void hmat_register_target_initiators(struct memory_target *target)
>   	 * initiators.
>   	 */
>   	bitmap_zero(p_nodes, MAX_NUMNODES);
> -	list_sort(p_nodes, &initiators, initiator_cmp);
> +	list_sort(NULL, &initiators, initiator_cmp);
> +	if (initiators_to_nodemask(p_nodes) < 0)
> +		return;
> +
>   	if (!access0done) {
>   		for (i = WRITE_LATENCY; i <= READ_BANDWIDTH; i++) {
>   			loc = localities_types[i];
> @@ -643,7 +655,9 @@ static void hmat_register_target_initiators(struct memory_target *target)
>   
>   	/* Access 1 ignores Generic Initiators */
>   	bitmap_zero(p_nodes, MAX_NUMNODES);
> -	list_sort(p_nodes, &initiators, initiator_cmp);
> +	if (initiators_to_nodemask(p_nodes) < 0)
> +		return;
> +
>   	for (i = WRITE_LATENCY; i <= READ_BANDWIDTH; i++) {
>   		loc = localities_types[i];
>   		if (!loc)
>