memcg is disabled in v5.15 RT kernel (known issue)

[Krzysztof Kozlowski]

From v5.15.2-rt20 announcement:
  Known issues:
  - The "Memory controller" (CONFIG_MEMCG) has been disabled.

This might be the cause of ubuntu_ltp_controllers failure - ubuntu_ltp_controllers.pids_1_100:
##########
COMMAND: /opt/ltp/bin/ltp-pan -q -e -S -a 466487 -n 466487 -f /tmp/ltp-DbBcUelSWj/alltests -l /dev/null -C /dev/null -T /dev/null
LOG File: /dev/null
FAILED COMMAND File: /dev/null
TCONF COMMAND File: /dev/null
Running tests.......
pids 1 TINFO: timeout per run is 0h 5m 0s
mount: /dev/cgroup: none already mounted on /sys/fs/bpf.
pids 1 TBROK: mount -t cgroup -o pids none /dev/cgroup failed
pids 1 TINFO: removing created directories
rmdir: failed to remove '/dev/cgroup/ltp_pids_1': No such file or directory
pids 1 TINFO: Umounting pids
umount: /dev/cgroup: not mounted.
pids 1 TINFO: AppArmor enabled, this may affect test results
pids 1 TINFO: it can be disabled with TST_DISABLE_APPARMOR=1 (requires super/root)
pids 1 TINFO: loaded AppArmor profiles: none
##########

[Ubuntu Kernel Bot (ubuntu-kernel-bot)]

This bug is missing log files that will aid in diagnosing the problem. While running an Ubuntu kernel (not a mainline or third-party kernel) please enter the following command in a terminal window:

apport-collect 1953345

and then change the status of the bug to 'Confirmed'.

If, due to the nature of the issue you have encountered, you are unable to run this command, please add a comment stating that fact and change the bug status to 'Confirmed'.

This change has been made by an automated script, maintained by the Ubuntu Kernel Team.

[Po-Hsu Lin (cypressyew)]

This issue does not exist on J-realtime anymore.

 INFO: Test start time: Tue Aug 16 06:08:56 UTC 2022
 COMMAND: /opt/ltp/bin/ltp-pan -q -e -S -a 648348 -n 648348 -f /tmp/ltp-qVqxKBH0Bi/alltests -l /dev/null -C /dev/null -T /dev/null
 LOG File: /dev/null
 FAILED COMMAND File: /dev/null
 TCONF COMMAND File: /dev/null
 Running tests.......
 pids 1 TINFO: timeout per run is 0h 5m 0s
 pids 1 TINFO: test starts with cgroup version 2
 pids 1 TINFO: Running testcase 1 with 1 processes
 pids 1 TPASS: fork didn't fail

 Summary:
 passed 1
 failed 0
 broken 0
 skipped 0
 warnings 0
 INFO: ltp-pan reported all tests PASS
 LTP Version: 20220527
 INFO: Test end time: Tue Aug 16 06:08:56 UTC 2022