cgroup_regression_test.sh: test 2 TFAIL: Failed to mount cgroup filesystem

[quantienvu]

I'm testing LTP (20250530) on a custom arm64 board with Linux kernel 6.12 (aarch64).

The test cgroup_regression_test.sh fails when running full script:

• test1 PASS (no kernel bug found)
• test2 TFAIL: Failed to mount cgroup filesystem _(Fail randomly when testing on Non-RT and always Fail on RT).

cgroup_regression_test 1 TINFO: Running: cgroup_regression_test.sh
cgroup_regression_test 1 TINFO: Tested kernel: Linux rzt2h-dev 6.12.43-cip7-rt12-yocto-standard-g2d0564b7f225 #1 SMP PREEMPT_RT Thu Nov 20 07:48:25 UTC 2025 aarch64 GNU/Linux
cgroup_regression_test 1 TINFO: Using /tmp/ltp-XXXX7zpxiz/LTP_cgroup_regression_test.XXXXyTYH7B as tmpdir (tmpfs filesystem)
cgroup_regression_test 1 TINFO: timeout per run is 0h 5m 0s
cgroup_regression_test 1 TPASS: no kernel bug was found
mount: /tmp/ltp-XXXX7zpxiz/LTP_cgroup_regression_test.XXXXyTYH7B/cgroup: cgroup already mounted or mount point busy.
       dmesg(1) may have more information after failed mount system call.
cgroup_regression_test 2 TFAIL: Failed to mount cgroup filesystem
cgroup_regression_test 3 TCONF: CONFIG_SCHED_DEBUG is not enabled
cgroup_regression_test 4 TCONF: CONFIG_LOCKDEP is not enabled
cgroup_regression_test 5 TINFO: The '/tmp/ltp-XXXX7zpxiz/LTP_cgroup_regression_test.XXXXyTYH7B/cgroup' is not mounted, skipping umount
cgroup_regression_test 5 TPASS: no kernel bug was found
cgroup_regression_test 6 TPASS: no kernel bug was found
cgroup_regression_test 7 TPASS: no kernel bug was found for test 1
[ 2669.048048] option changes via remount are deprecated (pid=171382 comm=mount)
cgroup_regression_test 7 TCONF: skip rest of testing due possible oops triggered by reading /proc/sched_debug
cgroup_regression_test 7 TPASS: no kernel bug was found for test 2
[ 2669.124206] netlink: 'cgroup_regressi': attribute type 1 has an invalid length.
cgroup_regression_test 8 TPASS: no kernel bug was found

Reason Fail: Script runs too fast, doesn't wait for kernel to clean up.→ next mount fails.

When skip test1 or run individual test2 => PASS.

Workaround:

• Add sleep 1 or sync after umount cgroup/ in test1() (proven workaround from cgroup_regression_test.sh easily FAILs with "Device or resource busy" #839).

Please help me check it.

Thanks!