ACPI / processor: Fix STARTING/DYING action in acpi_cpu_soft_notify()

During CPU online/offline testing on a large system, one of the
processors got stuck after the message "bad: scheduling from the
idle thread!".  The problem is that acpi_cpu_soft_notify() calls
acpi_bus_get_device() for all action types.  CPU_STARTING and
CPU_DYING do not allow the notify handlers to sleep.  However,
acpi_bus_get_device() can sleep in acpi_ut_acquire_mutex().

Change acpi_cpu_soft_notify() to return immediately for CPU_STARTING
and CPU_DYING as they have no action in this handler.
Signed-off-by: Toshi Kani <toshi.kani@hp.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/processor_driver.c

@@ -121,6 +121,13 @@ static int acpi_cpu_soft_notify(struct notifier_block *nfb,
 	struct acpi_processor *pr = per_cpu(processors, cpu);
 	struct acpi_device *device;
 
+	/*
+	 * CPU_STARTING and CPU_DYING must not sleep. Return here since
+	 * acpi_bus_get_device() may sleep.
+	 */
+	if (action == CPU_STARTING || action == CPU_DYING)
+		return NOTIFY_DONE;
+
 	if (!pr || acpi_bus_get_device(pr->handle, &device))
 		return NOTIFY_DONE;