Hello I encountered a problem when I try to unmount the subsystem right after all it's subcgroups are removed, the cgroup_root would remain. Mounting this subsystem to another cgroup_root would return -EBUSY. The problem could be reproduced with the following script. test.sh: mkdir /tmp/test1 mount -t cgroup -o pids pids /tmp/test1 mkdir /tmp/test1/test rmdir /tmp/test1/test umount /tmp/test1 mkdir /tmp/test mount -t cgroup -o pids,cpu none /tmp/test test.sh should return this. mount: mounting none on /tmp/test failed: Device or resource busy. It seems that when unmounting /tmp/test1, the original cgroup_root for this PID is not released. /test # cat /proc/cgroups #subsys_name hierarchy num_cgroups enabled cpuset 0 1 1 cpu 0 1 1 cpuacct 0 1 1 blkio 0 1 1 devices 0 1 1 freezer 0 1 1 net_cls 0 1 1 perf_event 0 1 1 net_prio 0 1 1 hugetlb 0 1 1 pids 1 1 1 rdma 0 1 1 misc 0 1 1 debug 0 1 1
