Merge "cpu-hotplug: Always use real time scheduling when hotplugging a CPU"

kernel/cpu.c

@@ -530,9 +530,41 @@ out:
 	return ret;
 }
 
+static int switch_to_rt_policy(void)
+{
+	struct sched_param param = { .sched_priority = MAX_RT_PRIO - 1 };
+	unsigned int policy = current->policy;
+	int err;
+
+	/* Nobody should be attempting hotplug from these policy contexts. */
+	if (policy == SCHED_BATCH || policy == SCHED_IDLE ||
+					policy == SCHED_DEADLINE)
+		return -EPERM;
+
+	if (policy == SCHED_FIFO || policy == SCHED_RR)
+		return 1;
+
+	/* Only SCHED_NORMAL left. */
+	err = sched_setscheduler_nocheck(current, SCHED_FIFO, &param);
+	return err;
+
+}
+
+static int switch_to_fair_policy(void)
+{
+	struct sched_param param = { .sched_priority = 0 };
+
+	return sched_setscheduler_nocheck(current, SCHED_NORMAL, &param);
+}
+
 int cpu_up(unsigned int cpu)
 {
 	int err = 0;
+	int switch_err = 0;
+
+	switch_err = switch_to_rt_policy();
+	if (switch_err < 0)
+		return switch_err;
 
 	if (!cpu_possible(cpu)) {
 		pr_err("can't online cpu %d because it is not configured as may-hotadd at boot time\n",
@@ -558,6 +590,13 @@ int cpu_up(unsigned int cpu)
 
 out:
 	cpu_maps_update_done();
+
+	if (!switch_err) {
+		switch_err = switch_to_fair_policy();
+		pr_err("Hotplug policy switch err. Task %s pid=%d\n",
+					current->comm, current->pid);
+	}
+
 	return err;
 }
 EXPORT_SYMBOL_GPL(cpu_up);