Proper error-handling of cdev_add() after cdev_alloc() ?

[Philipp Matthias Hahn <pmhahn@pmhahn.de>]

Hello,

How should errors of `cdev_add()` after `cdev_alloc()` be handled?


The basic schema seems to be like this:

	cdev = cdev_alloc();
	if (!cdev)
		return -ENOMEM;
	...
	ret = cdev_add(cdev, ...);
	if (ret < 0) {
		/* WHAT HERE ??? */
		return ret;
	}
	...
	return 0;  // success

I found 5 case of how errors are handled:

1.  kfree(cdev);
	drivers/media/v4l2-core/v4l2-dev.c:1060

2.  kobject_put(&cdev->kobj);
	drivers/char/xillybus/xillybus_class.c:107
	fs/char_dev.c:293
	drivers/s390/char/vmlogrdr.c:780
	drivers/tty/tty_io.c:3171
	drivers/uio/uio.c:925

3.  cdev_del(cdev);
	drivers/char/virtio_console.c:1435
	fs/fuse/cuse.c:419
	drivers/misc/mei/main.c:1318
	drivers/s390/char/tape_class.c:92
	drivers/s390/char/vmur.c:928
	drivers/scsi/sg.c:1560
	drivers/scsi/st.c:4307
	drivers/staging/vme_user/vme_user.c:694

4.  No error handling at all.
	arch/sh/boards/mach-landisk/gio.c:145

5.  panic()

Currently I'm unsure of what's the correct way.
My current understanding is, that `cdev_del()` should only be called if
`cdev_add()` succeeded, so those 8 findings above should be fixed. But
to what?

Thank you in advance
Philipp