[bug report] x86, sched: Bail out of frequency invariance if turbo frequency is unknown

[Dan Carpenter <dan.carpenter@oracle.com>]

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