Re: [PATCH] Revert "ACPI: CPPC: Fix remaining for_each_possible_cpu() to use online CPUs"
From: Jinjie Ruan
Date: Thu Apr 16 2026 - 22:03:41 EST
On 4/17/2026 3:36 AM, Sean Kelley wrote:
> On 4/16/26 1:52 AM, Jinjie Ruan wrote:
>> This reverts commit 56eb0c0ed345da7815274aa821a8546a073d7e97, because
>> this commit cause warning call trace below when concurrently bringing up
>> and down two SMT threads of a physical core.
>>
>> 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, related_cpus: 220, 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.
>>
>> 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.
>
>
> Yep, agree that using for_each_online_cpu() in acpi_get_psd_map()
> drops valid domain members and breaks the hotplug case you described.
>
> But a plain revert also re-exposes the nosmt bug. On systems where a
> possible CPU is never probed, per_cpu(cpc_desc_ptr, i) is NULL and
> acpi_get_psd_map() currently hits goto err_fault instead of just
> skipping that CPU.
I have a question regarding the original issue where it states 'This
breaks systems booted with "nosmt" or "nosmt=force"'. As far as I know,
the 'nosmt' parameter is only supported on x86. However, it seems the
current x86 kernel does not support enabling CONFIG_ACPI_CPPC_CPUFREQ
(only supported on arm64/arm/riscv). Could you please share the details
of your testing environment?
>
> So I think the fix is to restore for_each_possible_cpu() for the PSD
> map, but change the NULL case to continue:
I agree.
>
> --- a/drivers/acpi/cppc_acpi.c
> +++ b/drivers/acpi/cppc_acpi.c
> @@ -530,7 +530,7 @@
>
> match_cpc_ptr = per_cpu(cpc_desc_ptr, i);
> if (!match_cpc_ptr)
> - goto err_fault;
> + continue;
>
> match_pdomain = &(match_cpc_ptr->domain_info);
>
> That way offline CPUs with valid descriptors remain in shared_cpu_map
> (fixing the hotplug trace), while never-probed CPUs are skipped
> instead of failing map construction.
>
> The send_pcc_cmd() hunk already does if (!desc) continue, so reverting
> that loop back to for_each_possible_cpu() looks fine as-is.
>
> Happy to send the continue fix as a patch on top, or please feel free
> to fold it into yours if that makes sense.
Thanks! I will fold your fix into my patch and add your Co-developed-by
tag in the next version.
>
> Sean
>
>>
>> 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")
>> Signed-off-by: Jinjie Ruan <ruanjinjie@xxxxxxxxxx>
>> ---
>> drivers/acpi/cppc_acpi.c | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
>> index f0e513e9ed5d..9ae29f2c6db8 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)
>> @@ -524,7 +524,7 @@ 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;
>>
>
>