Re: [PATCH] cpufreq: amd-pstate-ut: fix null pointer dereference
From: Mario Limonciello
Date: Tue Jul 14 2026 - 13:16:38 EST
On 7/14/26 06:08, Zhongqiu Han wrote:
Hi Qianheng,
On 7/14/2026 6:22 PM, Qianheng Peng wrote:
Hello K Prateek,
Thanks for questions.
On 7/14/2026 14:39, K Prateek Nayak wrote:
On 7/14/2026 1:29 PM, Qianheng Peng wrote:No, it's Intel(R) Xeon(R) Gold 5128.
The crash issue may occur when insmod amd_pstate_ut modules.
amd_pstate_ut: 1 amd_pstate_ut_acpi_cpc_valid success!
amd_pstate_ut: 2 amd_pstate_ut_check_enabled success!
BUG: kernel NULL pointer dereference, address: 0000000000000080
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 0 P4D 0
Oops: 0000 [#1] SMP NOPTI
CPU: 0 PID: 20300 Comm: modprobe
Kdump: loaded Tainted: G O 6.6.0-0010.rc1.ctl4.x86_64 #1
Hardware name: FiberHome R2200 V5/Xeon Boards, BIOS 3.1a 02/24/2020
Is this an AMD platform?
In this machine, I got output as follow:RIP: 0010:amd_pstate_ut_check_perf+0x141/0x280 [amd_pstate_ut]
Call Trace:
<TASK>
amd_pstate_ut_init+0x1b/0xff0 [amd_pstate_ut]
? __pfx_amd_pstate_ut_init+0x10/0x10 [amd_pstate_ut]
do_one_initcall+0x42/0x2e0
? kmalloc_trace+0x26/0x90
do_init_module+0x60/0x240
__se_sys_init_module+0x185/0x1c0
do_syscall_64+0x62/0x190
entry_SYSCALL_64_after_hwframe+0x76/0x7e
</TASK>
Add invalidation check of cpudata in amd_pstate_ut_check_perf() and
amd_pstate_ut_check_freq() to avoid unpredicated null pointer dereference.
Fixes: 14eb1c96e3a3 ("cpufreq: amd-pstate: Add test module for amd- pstate driver")
Suggested-by: Li Xiong <xiongl24@xxxxxxxxxxxxxxx>
Suggested-by: Xibo Wang <wangxb12@xxxxxxxxxxxxxxx>
Signed-off-by: Qianheng Peng <pengqh1@xxxxxxxxxxxxxxx>
---
drivers/cpufreq/amd-pstate-ut.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/drivers/cpufreq/amd-pstate-ut.c b/drivers/cpufreq/amd- pstate-ut.c
index 735b29f..3b24260 100644
--- a/drivers/cpufreq/amd-pstate-ut.c
+++ b/drivers/cpufreq/amd-pstate-ut.c
@@ -157,6 +157,10 @@ static int amd_pstate_ut_check_perf(u32 index)
if (!policy)
continue;
cpudata = policy->driver_data;
+ if (!cpudata) {
+ pr_err("%s driver_data of %s is empty!\n", __func__, policy->kobj.name);
+ return -EINVAL;
+ }
if (get_shared_mem()) {
ret = cppc_get_perf_caps(cpu, &cppc_perf);
@@ -229,6 +233,10 @@ static int amd_pstate_ut_check_freq(u32 index)
if (!policy)
continue;
cpudata = policy->driver_data;
+ if (!cpudata) {
+ pr_err("%s driver_data of %s is empty!\n", __func__, policy->kobj.name);
+ return -EINVAL;
+ }
The only time I think this can happen is when the amd-pstate-ut races with a
the amd_pstate.*_cpu_exit() (probably as a result of concurrent mode switch)
or if you are running this without running amd-pstate as the cpufreq driver
(which the ut doesn't check for beforehand)
My setup fails at this exact same point when I have the driver unloaded.
What is the output of following before you run into this issue:
cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_driver
cat /sys/devices/system/cpu/amd_pstate/status
Are you doing any concurrent hotplug / mode switch?
if (!((policy->cpuinfo.max_freq >= cpudata- >nominal_freq) &&
(cpudata->nominal_freq > cpudata- >lowest_nonlinear_freq) &&
======================================================================================
[root@ ~]# cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_driver
intel_cpufreq
[root@ ~]# cat /sys/devices/system/cpu/amd_pstate/status
cat: /sys/devices/system/cpu/amd_pstate/status: No such file or directory (os error 2)
======================================================================================
Otherwise,I didn't do any concurrent hotplug / mode switch, just modprobe amd_pstate_ut.
It may be worth adding driver name detection to this ut driver, for
example via cpufreq_get_current_driver().
Yeah I agree with this direction.