[PATCH v2] ACPI: CPPC: Fix related_cpus inconsistency during CPU hotplug

[Jinjie Ruan]

When concurrently bringing up and down two SMT threads of a physical
core, many warning call traces occur as below:

The issue timeline is as follows:

1. when the system starts,
	cpufreq: cpu: 220, policy->related_cpus: 220-221, policy->cpus: 220-221

2. Offline cpu 220 and cpu 221.

3. Online cpu 220
- cpu 221 is now offline, as acpi_get_psd_map() use for_each_online_cpu(),
  so the cpu_data->shared_cpu_map, policy->cpus, and related_cpus has only
  cpu 220.
	cpufreq: cpu: 220, policy->related_cpus: 220, policy->cpus: 220

4. offline cpu 220

5. online cpu 221, the below call trace occurs:
- Because cpu 220 and cpu 221 share one policy, and policy->related_cpus
  = 220 after step 3, so cpu 221 is not in policy->related_cpus
  but per_cpu(cpufreq_cpu_data, cpu221) is not NULL.

After revert commit 56eb0c0ed345 ("ACPI: CPPC: Fix remaining
for_each_possible_cpu() to use online CPUs"), the issue disappeared.

The _PSD (P-State Dependency) defines the hardware-level dependency of
frequency control across CPU cores. Since this relationship is a physical
attribute of the hardware topology, it remains constant regardless of the
online or offline status of the CPUs.

Using for_each_online_cpu() in acpi_get_psd_map() is problematic. If a
CPU is offline, it will be excluded from the shared_cpu_map.
Consequently, if that CPU is brought online later, the kernel will fail to
recognize it as part of any shared frequency domain.

Switch back to for_each_possible_cpu() to ensure that all cores defined
in the ACPI tables are correctly mapped into their respective performance
domains from the start. This aligns with the logic of policy->related_cpus,
which must encompass all potentially available cores in the domain to
prevent logic gaps during CPU hotplug operations.

To resolve the original issue regarding the "nosmt" or "nosmt=force"
boot parameter, as send_pcc_cmd() function already does if (!desc)
continue, so reverting that loop back to for_each_possible_cpu() is ok,
only need to change the match_cpc_ptr NULL case in acpi_get_psd_map() to
continue as Sean suggested.

How to reproduce, on arm64 machine with SMT support which use acpi cppc
cpufreq driver:

	bash test.sh 220 & bash test.sh 221 &

	The test.sh is as below:
		while true
			do
			echo 0 > /sys/devices/system/cpu/cpu${1}/online
			sleep 0.5
			cat /sys/devices/system/cpu/cpu${1}/cpufreq/related_cpus
			echo 1 >  /sys/devices/system/cpu/cpu${1}/online
			cat /sys/devices/system/cpu/cpu${1}/cpufreq/related_cpus
		done

	CPU: 221 PID: 1119 Comm: cpuhp/221 Kdump: loaded Not tainted 6.6.0debug+ #5
	Hardware name: To be filled by O.E.M. S920X20/BC83AMDA01-7270Z, BIOS 20.39 09/04/2024
	pstate: a1400009 (NzCv daif +PAN -UAO -TCO +DIT -SSBS BTYPE=--)
	pc : cpufreq_online+0x8ac/0xa90
	lr : cpuhp_cpufreq_online+0x18/0x30
	sp : ffff80008739bce0
	x29: ffff80008739bce0 x28: 0000000000000000 x27: ffff28400ca32200
	x26: 0000000000000000 x25: 0000000000000003 x24: ffffd483503ff000
	x23: ffffd483504051a0 x22: ffffd48350024a00 x21: 00000000000000dd
	x20: 000000000000001d x19: ffff28400ca32000 x18: 0000000000000000
	x17: 0000000000000020 x16: ffffd4834e6a3fc8 x15: 0000000000000020
	x14: 0000000000000008 x13: 0000000000000001 x12: 00000000ffffffff
	x11: 0000000000000040 x10: ffffd48350430728 x9 : ffffd4834f087c78
	x8 : 0000000000000001 x7 : ffff2840092bdf00 x6 : ffffd483504264f0
	x5 : ffffd48350405000 x4 : ffff283f7f95cc60 x3 : 0000000000000000
	x2 : ffff53bc2f94b000 x1 : 00000000000000dd x0 : 0000000000000000
	Call trace:
	 cpufreq_online+0x8ac/0xa90
	 cpuhp_cpufreq_online+0x18/0x30
	 cpuhp_invoke_callback+0x128/0x580
	 cpuhp_thread_fun+0x110/0x1b0
	 smpboot_thread_fn+0x140/0x190
	 kthread+0xec/0x100
	 ret_from_fork+0x10/0x20
	---[ end trace 0000000000000000 ]---

Cc: stable@xxxxxxxxxxxxxxx
Fixes: 56eb0c0ed345 ("ACPI: CPPC: Fix remaining for_each_possible_cpu() to use online CPUs")
Co-developed-by: Sean Kelley <skelley@xxxxxxxxxx>
Signed-off-by: Sean Kelley <skelley@xxxxxxxxxx>
Signed-off-by: Jinjie Ruan <ruanjinjie@xxxxxxxxxx>
---
v2:
- Fix the original issue by continue if per_cpu(cpc_desc_ptr, i) is NULL.
- Update the commit message
---
 drivers/acpi/cppc_acpi.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
index f0e513e9ed5d..bcfe2e6b8445 100644
--- a/drivers/acpi/cppc_acpi.c
+++ b/drivers/acpi/cppc_acpi.c
@@ -362,7 +362,7 @@ static int send_pcc_cmd(int pcc_ss_id, u16 cmd)
 end:
 	if (cmd == CMD_WRITE) {
 		if (unlikely(ret)) {
-			for_each_online_cpu(i) {
+			for_each_possible_cpu(i) {
 				struct cpc_desc *desc = per_cpu(cpc_desc_ptr, i);
 
 				if (!desc)
@@ -524,13 +524,13 @@ int acpi_get_psd_map(unsigned int cpu, struct cppc_cpudata *cpu_data)
 	else if (pdomain->coord_type == DOMAIN_COORD_TYPE_SW_ANY)
 		cpu_data->shared_type = CPUFREQ_SHARED_TYPE_ANY;
 
-	for_each_online_cpu(i) {
+	for_each_possible_cpu(i) {
 		if (i == cpu)
 			continue;
 
 		match_cpc_ptr = per_cpu(cpc_desc_ptr, i);
 		if (!match_cpc_ptr)
-			goto err_fault;
+			continue;
 
 		match_pdomain = &(match_cpc_ptr->domain_info);
 		if (match_pdomain->domain != pdomain->domain)
-- 
2.34.1