Me too.
My system hang many time after update to the latest kernel
# uname -a
Linux proxmox2 4.2.8-1-pve #1 SMP Fri Feb 26 16:37:36 CET 2016 x86_64 GNU/Linux
This happen to me.
After investigate I found Proxmox 4.1 created VM with acltype=posixacl
# zfs get -r acltype /rpool/vm
NAME PROPERTY VALUE SOURCE
rpool/vm acltype off default
rpool/vm/subvol-100-disk-1 acltype off default...