Comment # 1 on bug 968629 from Patrick Schaaf

Possibly relevant to the issue: on all affected VMs, I run a self-built kernel
3.14.59 with most cgroup options disabled:

CONFIG_CGROUPS=y
# CONFIG_CGROUP_DEBUG is not set
# CONFIG_CGROUP_FREEZER is not set
# CONFIG_CGROUP_DEVICE is not set
# CONFIG_CGROUP_CPUACCT is not set
# CONFIG_CGROUP_PERF is not set
# CONFIG_CGROUP_SCHED is not set
# CONFIG_CGROUP_NET_PRIO is not set
CONFIG_CGROUP_NET_CLASSID=y

That was not an issue in the past. Normal cgroup grouping of processes works,
as can be seen with "systemctl status" on normal process groups.