ublk: detach gendisk from ublk device if add_disk() fails

Inside ublk_abort_requests(), gendisk is grabbed for aborting all
inflight requests. And ublk_abort_requests() is called when exiting
the uring context or handling timeout.

If add_disk() fails, the gendisk may have been freed when calling
ublk_abort_requests(), so use-after-free can be caused when getting
disk's reference in ublk_abort_requests().

Fixes the bug by detaching gendisk from ublk device if add_disk() fails.

Fixes: bd23f6c2 ("ublk: quiesce request queue when aborting queue")
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20241225110640.351531-1-ming.lei@redhat.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>