sched: add init_idle_bootup_task()

add the init_idle_bootup_task() callback to the bootup thread,
unused at the moment. (CFS will use it to switch the scheduling
class of the boot thread to the idle class)
Signed-off-by: Ingo Molnar <mingo@elte.hu>

include/linux/sched.h

@@ -195,6 +195,7 @@ struct task_struct;
 extern void sched_init(void);
 extern void sched_init_smp(void);
 extern void init_idle(struct task_struct *idle, int cpu);
+extern void init_idle_bootup_task(struct task_struct *idle);
 
 extern cpumask_t nohz_cpu_mask;
 #if defined(CONFIG_SMP) && defined(CONFIG_NO_HZ)

init/main.c

@@ -436,8 +436,9 @@ static void noinline __init_refok rest_init(void)
 
 	/*
 	 * The boot idle thread must execute schedule()
-	 * at least one to get things moving:
+	 * at least once to get things moving:
 	 */
+	init_idle_bootup_task(current);
 	preempt_enable_no_resched();
 	schedule();
 	preempt_disable();

kernel/sched.c

@@ -5018,6 +5018,11 @@ void show_state_filter(unsigned long state_filter)
 		debug_show_all_locks();
 }
 
+void __cpuinit init_idle_bootup_task(struct task_struct *idle)
+{
+	/* nothing yet */
+}
+
 /**
  * init_idle - set up an idle thread for a given CPU
  * @idle: task in question