alloc_disk() should set the kobject's subsystem before calling kobject_init(), 
which would increment the subsystem's refcount (to be decremented in 
kobject_cleanup()). Since it was being set after the call, the subsystem's 
refcount was being pushed to 0 if the floppy driver was enabled, but there 
were no floppy drives found (the driver would alloc_disk(), then put_disk() if 
no drives were found).


Partitions use kobject_register(), so they don't have to do kobject_init()
(it's done for them).

add_disk() should use kobject_add() instead of kobject_register(), since 
it's already done kobject_init() in alloc_disk().

Also, del_gendisk() doesn't have to do extra refcount and call
kobject_unregister(); it should just call kobject_del(). The block device
will be freed up later when put_disk() pushes the refcount to 0.