cpu_hotplug test failed because there is only 1 CPU

[Po-Hsu Lin]

On a KVM node, this test in the ubuntu_kernel_selftest will fail if there is only one CPU

 selftests: cpu-on-off-test.sh
 ========================================
 pid 479's current affinity mask: 1
 pid 479's new affinity mask: 1
 CPU online/offline summary:
 skip all tests:: since there is only one cpu: 0
 not ok 1..1 selftests: cpu-on-off-test.sh [FAIL]

Maybe we should not mark this as failed if it's skipped.

[Po-Hsu Lin (cypressyew)]

The script will return 4 if the test was skipped.

ksft_skip=4

 if [[ "$online_cpus" = "$online_max" ]]; then
  echo "$msg: since there is only one cpu: $online_cpus"
  exit $ksft_skip
 fi

[Po-Hsu Lin (cypressyew)]

To make the skip code work, we will need to fix 1812352 first.
And bring the CPU hotplug skip code change to older releases if needed.

[Po-Hsu Lin (cypressyew)]

With bug 1812352 fixed, this is now affecting Xenial.

The kselftest framework in Xenial needs to be fixed as well. (bug 1851486)

[Po-Hsu Lin (cypressyew)]

Still visible in Xenial 4.4.0-1118.132 AWS t2.small

[Krzysztof Kozlowski (krzk)]

Found on xenial/linux-aws/4.4.0-1132.146