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

[Rafael J. Wysocki]

On Mon, Apr 27, 2026 at 4:29 AM Jinjie Ruan <ruanjinjie@xxxxxxxxxx> wrote:
>
>
>
> On 4/17/2026 12:01 PM, Jinjie Ruan wrote:
> > 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 ]---
>
> Gentle ping.

I've noticed it.

Now applied as 7.1 material, thanks!

> >
> > 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)
>
>