genhd: Make put_disk() safe for disks that have not been registered

genhd: Make put_disk() safe for disks that have not been registered

Since commit 523e1d3 ('block: make gendisk hold a reference to its
queue'), add_disk() adds a reference to disk->queue, which is then
dropped by disk_release().  But if a disk is destroyed without being
registered through add_disk() (or if add_disk() fails at the first
hurdle) then we have a reference imbalance.

Use the GENHD_FL_UP flag to tell whether this extra reference has been
added.  Remove the incomplete workaround from the floppy driver.

Cc: stable@vger.kernel.org
Acked-by: Herton Ronaldo Krzesinski <herton.krzesinski@canonical.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>