smp_ihk_release_cpu: Fix error handling

* Range-check CPU ID
* Error-return when trying to online onlined CPU

Change-Id: I437d3046333e54e7525d41c2d2ab1006846d003e

linux/driver/smp/smp-driver.c

@@ -3716,6 +3716,13 @@ static int smp_ihk_release_cpu(ihk_device_t ihk_dev, unsigned long arg)
 	memset(&cpus_to_online, 0, sizeof(cpus_to_online));
 
 	for (i = 0; i < req.num_cpus; i++) {
+		if (req_cpus[i] < 0 || req_cpus[i] >= nr_cpu_ids) {
+			pr_info("%s: error: CPU %d is out of range\n",
+				__func__, req_cpus[i]);
+
+			ret = -EINVAL;
+			goto out;
+		}
 		cpumask_set_cpu(req_cpus[i], &cpus_to_online);
 	}
 
@@ -3740,7 +3747,10 @@ static int smp_ihk_release_cpu(ihk_device_t ihk_dev, unsigned long arg)
 		}
 
 		if (cpu_online(cpu)) {
-			continue;
+			printk("IHK-SMP: error: CPU %d is online\n",
+			       cpu);
+			ret = -EINVAL;
+			goto err;
 		}
 
 		if (ihk_smp_cpus[cpu].status != IHK_SMP_CPU_AVAILABLE) {