Make idle loop not miss a chance to schedule

Prevents the case where McKernel misses one chance to schedule a
task when an interrupt occurs just after enabling interrupt and
just before executing "halt" in the idle loop (in kernel/process.c).

refs #45

arch/x86/kernel/cpu.c

@@ -510,6 +510,11 @@ void cpu_halt(void)
 	asm volatile("hlt");
 }
 
+void cpu_safe_halt(void)
+{
+    asm volatile("sti; hlt");
+}
+
 void cpu_enable_interrupt(void)
 {
 	asm volatile("sti");

kernel/process.c

@@ -1546,16 +1546,16 @@ void release_process(struct process *proc)
 
 static void idle(void)
 {
-	//unsigned int	flags;
-	//flags = ihk_mc_spinlock_lock(&cpu_status_lock);
-	//ihk_mc_spinlock_unlock(&cpu_status_lock, flags);
 	cpu_local_var(status) = CPU_STATUS_IDLE;
+    cpu_enable_interrupt();
 
 	while (1) {
-		cpu_enable_interrupt();
 		schedule();
-		//cpu_local_var(status) = CPU_STATUS_IDLE;
-		cpu_halt();
+        cpu_disable_interrupt();
+        if (cpu_local_var(status) == CPU_STATUS_IDLE)
+            cpu_safe_halt();
+        else
+            cpu_enable_interrupt();
 	}
 }
 

lib/include/ihk/cpu.h

@@ -19,6 +19,7 @@
 void cpu_enable_interrupt(void);
 void cpu_disable_interrupt(void);
 void cpu_halt(void);
+void cpu_safe_halt(void);
 void cpu_restore_interrupt(unsigned long);
 void cpu_pause(void);