ACPI / scan: Make namespace scanning and trimming mutually exclusive

There is no guarantee that acpi_bus_scan() and acpi_bus_trim() will
not be run in parallel for the same scope of the ACPI namespace,
which may lead to a great deal of confusion, so introduce a new mutex
to prevent that from happening.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Yinghai Lu <yinghai@kernel.org>

drivers/acpi/scan.c

@@ -52,6 +52,7 @@ static const struct acpi_device_id acpi_platform_device_ids[] = {
 
 static LIST_HEAD(acpi_device_list);
 static LIST_HEAD(acpi_bus_id_list);
+static DEFINE_MUTEX(acpi_scan_lock);
 DEFINE_MUTEX(acpi_device_lock);
 LIST_HEAD(acpi_wakeup_device_list);
 
@@ -1587,19 +1588,22 @@ static acpi_status acpi_bus_device_attach(acpi_handle handle, u32 lvl_not_used,
 int acpi_bus_scan(acpi_handle handle)
 {
 	void *device = NULL;
+	int error = 0;
+
+	mutex_lock(&acpi_scan_lock);
 
 	if (ACPI_SUCCESS(acpi_bus_check_add(handle, 0, NULL, &device)))
 		acpi_walk_namespace(ACPI_TYPE_ANY, handle, ACPI_UINT32_MAX,
 				    acpi_bus_check_add, NULL, NULL, &device);
 
 	if (!device)
-		return -ENODEV;
-
-	if (ACPI_SUCCESS(acpi_bus_device_attach(handle, 0, NULL, NULL)))
+		error = -ENODEV;
+	else if (ACPI_SUCCESS(acpi_bus_device_attach(handle, 0, NULL, NULL)))
 		acpi_walk_namespace(ACPI_TYPE_ANY, handle, ACPI_UINT32_MAX,
 				    acpi_bus_device_attach, NULL, NULL, NULL);
 
-	return 0;
+	mutex_unlock(&acpi_scan_lock);
+	return error;
 }
 EXPORT_SYMBOL(acpi_bus_scan);
 
@@ -1628,6 +1632,8 @@ static acpi_status acpi_bus_remove(acpi_handle handle, u32 lvl_not_used,
 
 void acpi_bus_trim(struct acpi_device *start)
 {
+	mutex_lock(&acpi_scan_lock);
+
 	/*
 	 * Execute acpi_bus_device_detach() as a post-order callback to detach
 	 * all ACPI drivers from the device nodes being removed.
@@ -1642,6 +1648,8 @@ void acpi_bus_trim(struct acpi_device *start)
 	acpi_walk_namespace(ACPI_TYPE_ANY, start->handle, ACPI_UINT32_MAX, NULL,
 			    acpi_bus_remove, NULL, NULL);
 	acpi_bus_remove(start->handle, 0, NULL, NULL);
+
+	mutex_unlock(&acpi_scan_lock);
 }
 EXPORT_SYMBOL_GPL(acpi_bus_trim);