cgroup: misc cleanups

* cgrp_dfl_implicit_ss_mask is ulong instead of u16 unlike other
  ss_masks.  Make it a u16.

* Move have_canfork_callback together with other callback ss_masks.

Signed-off-by: Tejun Heo <tj@kernel.org>

kernel/cgroup/cgroup.c

@@ -159,7 +159,7 @@ static bool cgrp_dfl_visible;
 static u16 cgrp_dfl_inhibit_ss_mask;
 
 /* some controllers are implicitly enabled on the default hierarchy */
-static unsigned long cgrp_dfl_implicit_ss_mask;
+static u16 cgrp_dfl_implicit_ss_mask;
 
 /* The list of hierarchy roots */
 LIST_HEAD(cgroup_roots);
@@ -178,13 +178,13 @@ static DEFINE_IDR(cgroup_hierarchy_idr);
 static u64 css_serial_nr_next = 1;
 
 /*
- * These bitmask flags indicate whether tasks in the fork and exit paths have
- * fork/exit handlers to call. This avoids us having to do extra work in the
- * fork/exit path to check which subsystems have fork/exit callbacks.
+ * These bitmasks identify subsystems with specific features to avoid
+ * having to do iterative checks repeatedly.
  */
 static u16 have_fork_callback __read_mostly;
 static u16 have_exit_callback __read_mostly;
 static u16 have_free_callback __read_mostly;
+static u16 have_canfork_callback __read_mostly;
 
 /* cgroup namespace for init task */
 struct cgroup_namespace init_cgroup_ns = {
@@ -195,9 +195,6 @@ struct cgroup_namespace init_cgroup_ns = {
 	.root_cset	= &init_css_set,
 };
 
-/* Ditto for the can_fork callback. */
-static u16 have_canfork_callback __read_mostly;
-
 static struct file_system_type cgroup2_fs_type;
 static struct cftype cgroup_base_files[];