x86: add C1E aware idle function, fix

On Tue, 17 Jun 2008, Rafael J. Wysocki wrote:
>
> BTW, with the C1E patches reverted I don't get the
> WARNING: at /home/rafael/src/linux-next/kernel/smp.c:215 smp_call_function_single+0x3d/0xa2
> in the log.  Thomas?

The BROADCAST_FORCE notification uses smp_function_call and therefor
must be run with interrupts enabled.

While at it, add a comment for the BROADCAST_EXIT notifier as well.
Reported-and-bisected-by: Rafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/process.c

@@ -267,14 +267,26 @@ static void c1e_idle(void)
 
 		if (!cpu_isset(cpu, c1e_mask)) {
 			cpu_set(cpu, c1e_mask);
-			/* Force broadcast so ACPI can not interfere */
+			/*
+			 * Force broadcast so ACPI can not interfere. Needs
+			 * to run with interrupts enabled as it uses
+			 * smp_function_call.
+			 */
+			local_irq_enable();
 			clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_FORCE,
 					   &cpu);
 			printk(KERN_INFO "Switch to broadcast mode on CPU%d\n",
 			       cpu);
+			local_irq_disable();
 		}
 		clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ENTER, &cpu);
+
 		default_idle();
+
+		/*
+		 * The switch back from broadcast mode needs to be
+		 * called with interrupts disabled.
+		 */
 		 local_irq_disable();
 		 clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_EXIT, &cpu);
 		 local_irq_enable();