cgroup: don't online subsystems before cgroup_name/path() are operational

While refactoring cgroup creation, a5bca2152036 ("cgroup: factor out
cgroup_create() out of cgroup_mkdir()") incorrectly onlined subsystems
before the new cgroup is associated with it kernfs_node.  This is fine
for cgroup proper but cgroup_name/path() depend on the associated
kernfs_node and if a subsystem makes the new cgroup_subsys_state
visible, which they're allowed to after onlining, it can lead to NULL
dereference.

The current code performs cgroup creation and subsystem onlining in
cgroup_create() and cgroup_mkdir() makes the cgroup and subsystems
visible afterwards.  There's no reason to online the subsystems early
and we can simply drop cgroup_apply_control_enable() call from
cgroup_create() so that the subsystems are onlined and made visible at
the same time.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Fixes: a5bca2152036 ("cgroup: factor out cgroup_create() out of cgroup_mkdir()") 
Cc: stable@vger.kernel.org # v4.6+

path: root/net/8021q/Makefile

#
# Makefile for the Linux VLAN layer.
#
obj-$(subst m,y,$(CONFIG_VLAN_8021Q))	+= vlan_core.o
obj-$(CONFIG_VLAN_8021Q)		+= 8021q.o

8021q-y					:= vlan.o vlan_dev.o vlan_netlink.o
8021q-$(CONFIG_VLAN_8021Q_GVRP)		+= vlan_gvrp.o
8021q-$(CONFIG_VLAN_8021Q_MVRP)		+= vlan_mvrp.o
8021q-$(CONFIG_PROC_FS)			+= vlanproc.o