On Thu, 2022-05-05 at 10:05 +0300, Dan Carpenter wrote:
> Hello Giovanni Gherdovich,
>
> The patch 51beea8862a3: "x86, sched: Bail out of frequency invariance
> if turbo frequency is unknown" from May 31, 2020, leads to the
> following Smatch static checker warning:
>
> arch/x86/kernel/cpu/aperfmperf.c:274 intel_set_max_freq_ratio()
> error: uninitialized symbol 'turbo_freq'.
>
> arch/x86/kernel/cpu/aperfmperf.c
> 242 static bool __init intel_set_max_freq_ratio(void)
> 243 {
> 244 u64 base_freq, turbo_freq;
> 245 u64 turbo_ratio;
> 246
> 247 if (slv_set_max_freq_ratio(&base_freq, &turbo_freq))
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
> Imagine this fails.
>
> 248 goto out;
> 249
> 250 if (x86_match_cpu(has_glm_turbo_ratio_limits) &&
> 251 skx_set_max_freq_ratio(&base_freq, &turbo_freq, 1))
> 252 goto out;
> 253
> 254 if (x86_match_cpu(has_knl_turbo_ratio_limits) &&
> 255 knl_set_max_freq_ratio(&base_freq, &turbo_freq, 1))
> 256 goto out;
> 257
> 258 if (x86_match_cpu(has_skx_turbo_ratio_limits) &&
> 259 skx_set_max_freq_ratio(&base_freq, &turbo_freq, 4))
> 260 goto out;
> 261
> 262 if (core_set_max_freq_ratio(&base_freq, &turbo_freq))
> 263 goto out;
> 264
> 265 return false;
> 266
> 267 out:
> 268 /*
> 269 * Some hypervisors advertise X86_FEATURE_APERFMPERF
> 270 * but then fill all MSR's with zeroes.
> 271 * Some CPUs have turbo boost but don't declare any turbo ratio
> 272 * in MSR_TURBO_RATIO_LIMIT.
> 273 */
> --> 274 if (!base_freq || !turbo_freq) {
> ^^^^^^^^^^^^^^^^^^^^^^^^^
> Uninitialized. Although I notice that base_freq is also unintialized
> and that predates your patch... So I should probably send this bug
> report to someone else... Sorry?
>
Hello Dan,
I'm the right person for this report, as I think I wrote both the buggy
patch and the buggy code that predates it. I'm taking a moment to check
what's going on, as that really look like a dumb mistake.
Thanks for the report, I'll follow up.
Giovanni
