I can replicate this on a Thinkpad X230i running archlinux with latest
4.14.7 kernel, without the ZFS modules.

Steps to reproduce:
1) create a virtual machine using libvirt (attached xml)
2) virsh start vm
3) head /sys/fs/cgroup/unified/machine.slice/machine-
qemu\\x2d2\\x2dvm.scope/cgroup.procs

This hangs the laptop requiring a hard reset.

Regards,
George