Re: [PATCH] Revert "ACPI: CPPC: Fix remaining for_each_possible_cpu() to use online CPUs"
From: Sean Kelley
Date: Thu Apr 16 2026 - 23:00:43 EST
On 4/16/26 7:00 PM, Jinjie Ruan wrote:
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?
Yeah, good question. However, nosmt is actually defined generically in kernel/cpu.c
(early_param("nosmt", smt_cmdline_disable)), not in any
arch-specific code, so it works on anything that selects HOTPLUG_SMT.
arm64 does:
arch/arm64/Kconfig select HOTPLUG_SMT if HOTPLUG_CPU
And acpi_get_psd_map() is called from drivers/cpufreq/cppc_cpufreq.c,
which has: depends on ARM || ARM64 || RISCV.
So the overlap where this bug actually triggers is arm64. Testing was
on an NVIDIA Vera (Olympus) platform booted with "nosmt". That's the
environment where the original -EFAULT failure in acpi_get_psd_map()
was reproduced.
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.
Sounds good, thanks.
Sean
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;