[LTP] [PATCH] cpufreq_intel: Check for per-CPU online file presence before reading

[LTP] [PATCH] cpufreq_intel: Check for per-CPU online file presence before reading

[Wake Liu via ltp]

From: Grzegorz Jaszczyk <jaszczyk@google.com>

In setup(), the test assumes that all secondary CPUs (cpu1..cpuN-1)
expose '/sys/devices/system/cpu/cpu<N>/online' and attempts to read
their status using SAFE_FILE_SCANF().

However, on systems where CPU hotplugging is disabled (e.g. kernels
built without CONFIG_HOTPLUG_CPU or platforms where CPUs are not
hotpluggable), the per-CPU 'online' sysfs attributes are not created.
Calling SAFE_FILE_SCANF() on a non-existent file results in ENOENT
and breaks test setup with TBROK.

Check for the existence of the per-CPU 'online' file with access()
first. If the file exists, read the status via SAFE_FILE_SCANF(); if
it does not exist, assume the CPU is not hotpluggable and is
permanently online.

Signed-off-by: Grzegorz Jaszczyk <jaszczyk@google.com>
Signed-off-by: Wake Liu <wakel@google.com>
---
 testcases/kernel/power_management/cpufreq_intel.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/testcases/kernel/power_management/cpufreq_intel.c b/testcases/kernel/power_management/cpufreq_intel.c
index 11896258e..a2a3f3475 100644
--- a/testcases/kernel/power_management/cpufreq_intel.c
+++ b/testcases/kernel/power_management/cpufreq_intel.c
@@ -94,8 +94,16 @@ static void setup(void)
 		int tmp;
 
 		snprintf(path, sizeof(path), "/sys/devices/system/cpu/cpu%d/online", i);
-		SAFE_FILE_SCANF(path, "%d", &tmp);
-		online[i] = (bool)tmp;
+		if (access(path, F_OK) == 0) {
+			SAFE_FILE_SCANF(path, "%d", &tmp);
+			online[i] = (bool)tmp;
+		} else {
+			/*
+			 * If the 'online' file is missing, the CPU is not
+			 * hotpluggable and is permanently online.
+			 */
+			online[i] = true;
+		}
 	}
 
 	SAFE_FILE_PRINTF("/sys/devices/system/cpu/intel_pstate/status", "active");
-- 
2.55.0.897.gb25b4bd76c-goog


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Re: [LTP] cpufreq_intel: Check for per-CPU online file presence before reading

[linuxtestproject.agent]

Hi Grzegorz,

On Aug 28, 2026, Grzegorz Jaszczyk wrote:
> cpufreq_intel: Check for per-CPU online file presence before reading

Verdict - Reviewed

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Note:

The agent can sometimes produce false positives although often its
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comment this email or ignore the suggestions.

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LTP AI Reviewer

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Re: [LTP] [PATCH] cpufreq_intel: Check for per-CPU online file presence before reading

[Kubaj, Piotr]

W dniu pią, 28.08.2026 o godzinie 23∶09 +0000, użytkownik Wake Liu
napisał:
> From: Grzegorz Jaszczyk <jaszczyk@google.com>
> 
> In setup(), the test assumes that all secondary CPUs (cpu1..cpuN-1)
> expose '/sys/devices/system/cpu/cpu<N>/online' and attempts to read
> their status using SAFE_FILE_SCANF().
> 
> However, on systems where CPU hotplugging is disabled (e.g. kernels
> built without CONFIG_HOTPLUG_CPU or platforms where CPUs are not
> hotpluggable), the per-CPU 'online' sysfs attributes are not created.
> Calling SAFE_FILE_SCANF() on a non-existent file results in ENOENT
> and breaks test setup with TBROK.
> 
> Check for the existence of the per-CPU 'online' file with access()
> first. If the file exists, read the status via SAFE_FILE_SCANF(); if
> it does not exist, assume the CPU is not hotpluggable and is
> permanently online.
> 
> Signed-off-by: Grzegorz Jaszczyk <jaszczyk@google.com>
> Signed-off-by: Wake Liu <wakel@google.com>
> ---
>  testcases/kernel/power_management/cpufreq_intel.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/testcases/kernel/power_management/cpufreq_intel.c
> b/testcases/kernel/power_management/cpufreq_intel.c
> index 11896258e..a2a3f3475 100644
> --- a/testcases/kernel/power_management/cpufreq_intel.c
> +++ b/testcases/kernel/power_management/cpufreq_intel.c
> @@ -94,8 +94,16 @@ static void setup(void)
>  		int tmp;
>  
>  		snprintf(path, sizeof(path),
> "/sys/devices/system/cpu/cpu%d/online", i);
> -		SAFE_FILE_SCANF(path, "%d", &tmp);
> -		online[i] = (bool)tmp;
> +		if (access(path, F_OK) == 0) {
> +			SAFE_FILE_SCANF(path, "%d", &tmp);
> +			online[i] = (bool)tmp;
> +		} else {
> +			/*
> +			 * If the 'online' file is missing, the CPU
> is not
> +			 * hotpluggable and is permanently online.
> +			 */
> +			online[i] = true;
> +		}
>  	}
>  
>  	SAFE_FILE_PRINTF("/sys/devices/system/cpu/intel_pstate/statu
> s", "active");

LGTM.
Reviewed-by: Piotr Kubaj <piotr.kubaj@intel.com>
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Re: [LTP] [PATCH] cpufreq_intel: Check for per-CPU online file presence before reading

[Andrea Cervesato via ltp]

Reviewed-by: Andrea Cervesato <andrea.cervesato@suse.com>

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Andrea Cervesato
SUSE QE Automation Engineer Linux
andrea.cervesato@suse.com

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Re: [LTP] [PATCH] cpufreq_intel: Check for per-CPU online file presence before reading

[Andrea Cervesato via ltp]

Merged, Thanks!

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Andrea Cervesato
SUSE QE Automation Engineer Linux
andrea.cervesato@suse.com

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