rapidio: utilize new cdev_device_add helper function

This driver did not originally set kobj.parent so it likely had
potential a use after free bug which this patch fixes.

We convert from device_register to device_initialize/cdev_device_add.
While we are at it we use put_device instead of kfree (as recommended
by the device_initialize documentation). We also remove an unnecessary
extra get_device from the code.
Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/rapidio/devices/rio_mport_cdev.c

@@ -2444,31 +2444,25 @@ static struct mport_dev *mport_cdev_add(struct rio_mport *mport)
 	mutex_init(&md->buf_mutex);
 	mutex_init(&md->file_mutex);
 	INIT_LIST_HEAD(&md->file_list);
-	cdev_init(&md->cdev, &mport_fops);
-	md->cdev.owner = THIS_MODULE;
-	ret = cdev_add(&md->cdev, MKDEV(MAJOR(dev_number), mport->id), 1);
-	if (ret < 0) {
-		kfree(md);
-		rmcd_error("Unable to register a device, err=%d", ret);
-		return NULL;
-	}
 
-	md->dev.devt = md->cdev.dev;
+	device_initialize(&md->dev);
+	md->dev.devt = MKDEV(MAJOR(dev_number), mport->id);
 	md->dev.class = dev_class;
 	md->dev.parent = &mport->dev;
 	md->dev.release = mport_device_release;
 	dev_set_name(&md->dev, DEV_NAME "%d", mport->id);
 	atomic_set(&md->active, 1);
 
-	ret = device_register(&md->dev);
+	cdev_init(&md->cdev, &mport_fops);
+	md->cdev.owner = THIS_MODULE;
+
+	ret = cdev_device_add(&md->cdev, &md->dev);
 	if (ret) {
 		rmcd_error("Failed to register mport %d (err=%d)",
 		       mport->id, ret);
 		goto err_cdev;
 	}
 
-	get_device(&md->dev);
-
 	INIT_LIST_HEAD(&md->doorbells);
 	spin_lock_init(&md->db_lock);
 	INIT_LIST_HEAD(&md->portwrites);
@@ -2513,8 +2507,7 @@ static struct mport_dev *mport_cdev_add(struct rio_mport *mport)
 	return md;
 
 err_cdev:
-	cdev_del(&md->cdev);
-	kfree(md);
+	put_device(&md->dev);
 	return NULL;
 }
 
@@ -2578,7 +2571,7 @@ static void mport_cdev_remove(struct mport_dev *md)
 	atomic_set(&md->active, 0);
 	mport_cdev_terminate_dma(md);
 	rio_del_mport_pw_handler(md->mport, md, rio_mport_pw_handler);
-	cdev_del(&(md->cdev));
+	cdev_device_del(&md->cdev, &md->dev);
 	mport_cdev_kill_fasync(md);
 
 	flush_workqueue(dma_wq);
@@ -2603,7 +2596,6 @@ static void mport_cdev_remove(struct mport_dev *md)
 
 	rio_release_inb_dbell(md->mport, 0, 0x0fff);
 
-	device_unregister(&md->dev);
 	put_device(&md->dev);
 }