sched: prevent out of bound access in sched_group_energy()

group_idle_state() can return INT_MAX + 1 which is undefined behaviour
when there is no CPUs in sched_group.  Prevent such by error correctly.

Change-Id: If9796c829c091e461231569dc38c5e5456f58037
Signed-off-by: Joonwoo Park <joonwoop@codeaurora.org>
Signed-off-by: Satya Durga Srinivasu Prabhala <satyap@codeaurora.org>
[clingutla@codeaurora.org: Fixed trivial merge conflicts and squashed
  msm-4.14 change]
Signed-off-by: Lingutla Chandrasekhar <clingutla@codeaurora.org>
(cherry picked from commit bb5b0e61527011e4ebfc4058713a9068da9e7492)

Author: Joonwoo Park

kernel/sched/fair.c

@@ -5792,6 +5792,9 @@ static int group_idle_state(struct energy_env *eenv, int cpu_idx)
 	for_each_cpu(i, sched_group_cpus(sg))
 		state = min(state, idle_get_state_idx(cpu_rq(i)));
 
+	if (unlikely(state == INT_MAX))
+		return -EINVAL;
+
 	/* Take non-cpuidle idling into account (active idle/arch_cpu_idle()) */
 	state++;
 
@@ -5858,7 +5861,7 @@ static int group_idle_state(struct energy_env *eenv, int cpu_idx)
  * The required scaling will be performed just one time, by the calling
  * functions, once we accumulated the contributons for all the SGs.
  */
-static void calc_sg_energy(struct energy_env *eenv)
+static int calc_sg_energy(struct energy_env *eenv)
 {
 	struct sched_group *sg = eenv->sg;
 	int busy_energy, idle_energy;
@@ -5887,6 +5890,8 @@ static void calc_sg_energy(struct energy_env *eenv)
 
 		/* Compute IDLE energy */
 		idle_idx = group_idle_state(eenv, cpu_idx);
+		if (unlikely(idle_idx < 0))
+			return idle_idx;
 		idle_power = sg->sge->idle_states[idle_idx].power;
 
 		idle_energy   = SCHED_CAPACITY_SCALE - sg_util;
@@ -5895,6 +5900,7 @@ static void calc_sg_energy(struct energy_env *eenv)
 		total_energy = busy_energy + idle_energy;
 		eenv->cpu[cpu_idx].energy += total_energy;
 	}
+	return 0;
 }
 
 /*
@@ -5956,7 +5962,8 @@ static int compute_energy(struct energy_env *eenv)
 				 * CPUs in the current visited SG.
 				 */
 				eenv->sg = sg;
-				calc_sg_energy(eenv);
+				if (calc_sg_energy(eenv))
+					return -EINVAL;
 
 				/* remove CPUs we have just visited */
 				if (!sd->child) {