ACPI: Fix stale pointer access to flags.lockable

During hot-remove, acpi_bus_hot_remove_device() calls ACPI _LCK
method when device->flags.lockable is set. However, this device
pointer is stale since the target acpi_device object has been
already kfree'd by acpi_bus_trim().

The flags.lockable indicates whether or not this ACPI object
implements _LCK method. Fix the stable pointer access by replacing
it with acpi_get_handle() to check if _LCK is implemented.

Signed-off-by: Toshi Kani <toshi.kani@hp.com>
Reviewed-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/scan.c

@@ -97,6 +97,7 @@ void acpi_bus_hot_remove_device(void *context)
 	struct acpi_eject_event *ej_event = (struct acpi_eject_event *) context;
 	struct acpi_device *device;
 	acpi_handle handle = ej_event->handle;
+	acpi_handle temp;
 	struct acpi_object_list arg_list;
 	union acpi_object arg;
 	acpi_status status = AE_OK;
@@ -117,13 +118,16 @@ void acpi_bus_hot_remove_device(void *context)
 		goto err_out;
 	}
 
+	/* device has been freed */
+	device = NULL;
+
 	/* power off device */
 	status = acpi_evaluate_object(handle, "_PS3", NULL, NULL);
 	if (ACPI_FAILURE(status) && status != AE_NOT_FOUND)
 		printk(KERN_WARNING PREFIX
 				"Power-off device failed\n");
 
-	if (device->flags.lockable) {
+	if (ACPI_SUCCESS(acpi_get_handle(handle, "_LCK", &temp))) {
 		arg_list.count = 1;
 		arg_list.pointer = &arg;
 		arg.type = ACPI_TYPE_INTEGER;