It's posiable that criu is able to attach to a process
and then it becomes a zombie.

$ while :; do bash ./zdtm.sh -C --freeze-cgroup /sys/fs/cgroup/freezer/test transition/fork || break; done
...
(00.000978) Error (ptrace.c:154): SEIZE 13666: task not stopped after seize
Signed-off-by: Andrew Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>