sched/core: Fix compilation error when cgroup not selected

When cgroup is disabled the following compilation error was hit

	kernel/sched/core.c: In function ‘uclamp_update_active_tasks’:
	kernel/sched/core.c:1081:23: error: storage size of ‘it’ isn’t known
	  struct css_task_iter it;
			       ^~
	kernel/sched/core.c:1084:2: error: implicit declaration of function ‘css_task_iter_start’; did you mean ‘__sg_page_iter_start’? [-Werror=implicit-function-declaration]
	  css_task_iter_start(css, 0, &it);
	  ^~~~~~~~~~~~~~~~~~~
	  __sg_page_iter_start
	kernel/sched/core.c:1085:14: error: implicit declaration of function ‘css_task_iter_next’; did you mean ‘__sg_page_iter_next’? [-Werror=implicit-function-declaration]
	  while ((p = css_task_iter_next(&it))) {
		      ^~~~~~~~~~~~~~~~~~
		      __sg_page_iter_next
	kernel/sched/core.c:1091:2: error: implicit declaration of function ‘css_task_iter_end’; did you mean ‘get_task_cred’? [-Werror=implicit-function-declaration]
	  css_task_iter_end(&it);
	  ^~~~~~~~~~~~~~~~~
	  get_task_cred
	kernel/sched/core.c:1081:23: warning: unused variable ‘it’ [-Wunused-variable]
	  struct css_task_iter it;
			       ^~
	cc1: some warnings being treated as errors
	make[2]: *** [kernel/sched/core.o] Error 1

Fix by protetion uclamp_update_active_tasks() with
CONFIG_UCLAMP_TASK_GROUP

Fixes: babbe17 ("sched/uclamp: Update CPU's refcount on TG's clamp changes")
Reported-by: Randy Dunlap <[email protected]>
Signed-off-by: Qais Yousef <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Tested-by: Randy Dunlap <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Vincent Guittot <[email protected]>
Cc: Patrick Bellasi <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Dietmar Eggemann <[email protected]>
Cc: Juri Lelli <[email protected]>
Cc: Ben Segall <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

Author: Qais Yousef

kernel/sched/core.c

@@ -1073,6 +1073,7 @@ uclamp_update_active(struct task_struct *p, enum uclamp_id clamp_id)
 	task_rq_unlock(rq, p, &rf);
 }
 
+#ifdef CONFIG_UCLAMP_TASK_GROUP
 static inline void
 uclamp_update_active_tasks(struct cgroup_subsys_state *css,
 			   unsigned int clamps)
@@ -1091,7 +1092,6 @@ uclamp_update_active_tasks(struct cgroup_subsys_state *css,
 	css_task_iter_end(&it);
 }
 
-#ifdef CONFIG_UCLAMP_TASK_GROUP
 static void cpu_util_update_eff(struct cgroup_subsys_state *css);
 static void uclamp_update_root_tg(void)
 {