[LTP] cpufreq.c: add new test for cpufreq sysfs interface validation

[linuxtestproject.agent@gmail.com]

Hi Piotr,

On 2026-04-22, Piotr Kubaj wrote:
> cpufreq.c: add new test for cpufreq sysfs interface validation

> +static long *previous_scaling_max_freq, *previous_scaling_min_freq;
> +
> +static void cleanup(void)
> +{
> [...]
> +               SAFE_FILE_PRINTF(path, "%ld", previous_scaling_max_freq[i]);
> [...]
> +               SAFE_FILE_PRINTF(path, "%ld", previous_scaling_min_freq[i]);

Both arrays are zeroed by SAFE_CALLOC in setup() and only populated
inside run(). If run() aborts before reaching the per-CPU save loops
(e.g. a SAFE_OPEN or SAFE_FILE_SCANF fails on an earlier cpufreq node),
cleanup() writes 0 to scaling_max_freq and scaling_min_freq for every
online CPU, leaving the system in an invalid state.

Read the original per-CPU values in setup() instead.

Pre-existing issues noticed in the surrounding code (not introduced
by this patch):

- cpufreq.c:116 — strstr(contents, "performance powersave") assumes
  a specific governor ordering that the kernel does not guarantee.
- cpufreq.c:170 — same issue for "performance schedutil".

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