2.5.44 Fix uninitialized device struct w/ add_disk()

This occurs w/ 2.5 device-mapper; add_disk() is called (w/ a possibly invalid gendisk). add_disk() calls register_disk(), which constructs the device struct (gendisk::disk_dev). First, the bus_id field is initialized, and then device_add() is called. However, device_add() does no initialization of the device struct. So, since the gendisk::disk_dev::parent list is NULL, the gendisk::disk_dev::node field is never initialized. Later on in device_add(), if an error has occurred, list_del_init(&dev->node) is called; dev->node is {NULL,NULL}, and an oops occurs.

Instead of calling device_add(), my patch makes register_disk() call device_register(). This appear to do the same thing as device_add(), but initializes the device struct before calling device_add().

It's not denial.  I'm just selective about the reality I accept.
	-- Bill Watterson

@@ -455,7 +455,7 @@
 	s = strchr(dev->bus_id, '/');
 	if (s)
 		*s = '!';
-	device_add(dev);
+	device_register(dev);
 	device_create_file(dev, &disk_attr_dev);
 	device_create_file(dev, &disk_attr_range);
 	device_create_file(dev, &disk_attr_size);

Wrong. If device-mapper doesn't create gendisk with alloc_disk() - it's their bug; if it does - initialization is already done at alloc_disk() time.

Fix driver instead of breaking generic code.