/etc/init.d/sysfs does not check if /sys/fs/cgroup is mounted, and fails to start properly with older kernels. The workaround is to create $ cat /etc/conf.d/sysfs rc_cgroups="NO" but it would be better if the init script would check for the mountpoint. The mount_misc() does check it, but mount_cgroups() does not.
This is fixed in git, commit de5cee2. Thanks for the report.