[Bug libc/27398] New: Sporadic failures in tst-cpu-features-cpuinfo

["siddhesh at sourceware dot org" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=27398

            Bug ID: 27398
           Summary: Sporadic failures in tst-cpu-features-cpuinfo
           Product: glibc
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: libc
          Assignee: unassigned at sourceware dot org
          Reporter: siddhesh at sourceware dot org
                CC: drepper.fsp at gmail dot com, hjl.tools at gmail dot com
  Target Milestone: ---

The following tests fail sporadically on my machine:

Checking HAS_CPU_FEATURE (HLE):
  HAS_CPU_FEATURE (HLE): 1
  cpuinfo (hle): 0
 *** failure ***
--
Checking HAS_CPU_FEATURE (RTM):
  HAS_CPU_FEATURE (RTM): 1
  cpuinfo (rtm): 0
 *** failure ***

Whenever it succeeds, HAS_CPU_FEATURE is 0 in both cases but every once in a
while it returns 1.

To reproduce:

while ./testrun.sh elf/tst-cpu-features-cpuinfo; do /bin/true; done

This exits on the first failed run.

My /proc/cpuinfo:

processor       : 7
vendor_id       : GenuineIntel
cpu family      : 6
model           : 142
model name      : Intel(R) Core(TM) i7-8665U CPU @ 1.90GHz
stepping        : 12
microcode       : 0xde
cpu MHz         : 877.111
cache size      : 8192 KB
physical id     : 0
siblings        : 8
core id         : 3
cpu cores       : 4
apicid          : 7
initial apicid  : 7
fpu             : yes
fpu_exception   : yes
cpuid level     : 22
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov
pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb
rdtscp lm constant_tsc art arch_perfmon pebs bts rep_good nopl xtopology
nonstop_tsc cpuid aperfmperf pni pclmulqdq dtes64 monitor ds_cpl vmx smx est
tm2 ssse3 sdbg fma cx16 xtpr pdcm pcid sse4_1 sse4_2 x2apic movbe popcnt
tsc_deadline_timer aes xsave avx f16c rdrand lahf_lm abm 3dnowprefetch
cpuid_fault epb invpcid_single ssbd ibrs ibpb stibp ibrs_enhanced tpr_shadow
vnmi flexpriority ept vpid ept_ad fsgsbase tsc_adjust bmi1 avx2 smep bmi2 erms
invpcid mpx rdseed adx smap clflushopt intel_pt xsaveopt xsavec xgetbv1 xsaves
dtherm ida arat pln pts hwp hwp_notify hwp_act_window hwp_epp md_clear
flush_l1d arch_capabilities
vmx flags       : vnmi preemption_timer invvpid ept_x_only ept_ad ept_1gb
flexpriority tsc_offset vtpr mtf vapic ept vpid unrestricted_guest ple
shadow_vmcs pml ept_mode_based_exec
bugs            : spectre_v1 spectre_v2 spec_store_bypass swapgs taa
itlb_multihit srbds
bogomips        : 4199.88
clflush size    : 64
cache_alignment : 64
address sizes   : 39 bits physical, 48 bits virtual
power management:

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