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?
275 pr_debug("Couldn't determine cpu base or turbo frequency, necessary for scale-invariant accounting.\n");
276 return false;
277 }
278
279 turbo_ratio = div_u64(turbo_freq * SCHED_CAPACITY_SCALE, base_freq);
280 if (!turbo_ratio) {
281 pr_debug("Non-zero turbo and base frequencies led to a 0 ratio.\n");
282 return false;
283 }
284
285 arch_turbo_freq_ratio = turbo_ratio;
286 arch_set_max_freq_ratio(turbo_disabled());
287
288 return true;
289 }
regards,
dan carpenter
