platform/x86: wmi: Instantiate all devices before adding them

At some point, we will want sub-drivers to get references to other
devices on the same WMI bus. This change is needed to avoid races.

This ends up simplifying the setup code and fixing some leaks, too.

This is based on the original work of Andy Lutomirski <luto@kernel.org>,
but includes several modifications, many in response to review from
Michał Kępień <kernel@kempniu.pl>:

  https://www.spinics.net/lists/platform-driver-x86/msg08201.html

Signed-off-by: Darren Hart (VMware) <dvhart@infradead.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Mario Limonciello <mario_limonciello@dell.com>
Cc: Pali Rohár <pali.rohar@gmail.com>
Cc: linux-kernel@vger.kernel.org
Cc: platform-driver-x86@vger.kernel.org
Cc: linux-acpi@vger.kernel.org
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/platform/x86/wmi.c

@@ -796,7 +796,7 @@ static struct device_type wmi_type_data = {
 	.release = wmi_dev_release,
 };
 
-static int wmi_create_device(struct device *wmi_bus_dev,
+static void wmi_create_device(struct device *wmi_bus_dev,
 			     const struct guid_block *gblock,
 			     struct wmi_block *wblock,
 			     struct acpi_device *device)
@@ -852,7 +852,7 @@ static int wmi_create_device(struct device *wmi_bus_dev,
 
 	}
 
-	return device_register(&wblock->dev.dev);
+	device_initialize(&wblock->dev.dev);
 }
 
 static void wmi_free_devices(struct acpi_device *device)
@@ -863,10 +863,7 @@ static void wmi_free_devices(struct acpi_device *device)
 	list_for_each_entry_safe(wblock, next, &wmi_block_list, list) {
 		if (wblock->acpi_device == device) {
 			list_del(&wblock->list);
-			if (wblock->dev.dev.bus)
-				device_unregister(&wblock->dev.dev);
-			else
-				kfree(wblock);
+			device_unregister(&wblock->dev.dev);
 		}
 	}
 }
@@ -899,11 +896,11 @@ static bool guid_already_parsed(struct acpi_device *device,
 static int parse_wdg(struct device *wmi_bus_dev, struct acpi_device *device)
 {
 	struct acpi_buffer out = {ACPI_ALLOCATE_BUFFER, NULL};
-	union acpi_object *obj;
 	const struct guid_block *gblock;
-	struct wmi_block *wblock;
+	struct wmi_block *wblock, *next;
+	union acpi_object *obj;
 	acpi_status status;
-	int retval;
+	int retval = 0;
 	u32 i, total;
 
 	status = acpi_evaluate_object(device->handle, "_WDG", NULL, &out);
@@ -936,19 +933,15 @@ static int parse_wdg(struct device *wmi_bus_dev, struct acpi_device *device)
 			continue;
 
 		wblock = kzalloc(sizeof(struct wmi_block), GFP_KERNEL);
-		if (!wblock)
-			return -ENOMEM;
+		if (!wblock) {
+			retval = -ENOMEM;
+			break;
+		}
 
 		wblock->acpi_device = device;
 		wblock->gblock = gblock[i];
 
-		retval = wmi_create_device(wmi_bus_dev, &gblock[i],
-					   wblock, device);
-		if (retval) {
-			put_device(&wblock->dev.dev);
-			wmi_free_devices(device);
-			goto out_free_pointer;
-		}
+		wmi_create_device(wmi_bus_dev, &gblock[i], wblock, device);
 
 		list_add_tail(&wblock->list, &wmi_block_list);
 
@@ -958,11 +951,27 @@ static int parse_wdg(struct device *wmi_bus_dev, struct acpi_device *device)
 		}
 	}
 
-	retval = 0;
+	/*
+	 * Now that all of the devices are created, add them to the
+	 * device tree and probe subdrivers.
+	 */
+	list_for_each_entry_safe(wblock, next, &wmi_block_list, list) {
+		if (wblock->acpi_device != device)
+			continue;
+
+		retval = device_add(&wblock->dev.dev);
+		if (retval) {
+			dev_err(wmi_bus_dev, "failed to register %pULL\n",
+				wblock->gblock.guid);
+			if (debug_event)
+				wmi_method_enable(wblock, 0);
+			list_del(&wblock->list);
+			put_device(&wblock->dev.dev);
+		}
+	}
 
 out_free_pointer:
 	kfree(out.pointer);
-
 	return retval;
 }