Tried with commenting out cgroup_controllers but with no change.
Tried also unmounting /sys/fs/cgroup and mount the cgroups in a subfolder hierarchy manually but it remounted still all together (I think this is related at the unmounting support going away, I'm with kernel 3.10-rc4 on the test machine).
So I had a look at Slackware's init system's scripts: /sys/fs/cgroup is mounted in /etc/rc.d/rc.S, the main one, so I tried changed it to automount in subfolders the available controllers
--- ./etc/rc.d/rc.S.orig 2012-09-13 21:38:34.000000000 +0200 +++ ./etc/rc.d/rc.S 2013-06-07 19:56:06.176366278 +0200 @@ -51,7 +51,14 @@ # Mount Control Groups filesystem interface:
if grep -wq cgroup /proc/filesystems ; then if [ -d /sys/fs/cgroup ]; then - mount -t cgroup cgroup /sys/fs/cgroup + # Mount a tmpfs as the cgroup filesystem root + /sbin/mount -t tmpfs cgroup_root /sys/fs/cgroup
+ # Mount individual cgroup controllers: + controllers="$(/usr/bin/lssubsys -a 2>/dev/null | tr '\n' ' ' | /usr/bin/sed s/.$//)" + for i in $controllers; do + /usr/bin/mkdir /sys/fs/cgroup/$i
+ /sbin/mount -t cgroup -o $i $i /sys/fs/cgroup/$i + done else mkdir -p /dev/cgroup mount -t cgroup cgroup /dev/cgroup
This way virtual machines start fine, thanks a lot Daniel :)