Ceph » rbd

I found during some failure injection testing that the call to
rbd_free_disk() in the error path of rbd_dev_probe_finish() was
dropping an extra reference to the disk queue. The problem
occurred when put_disk tried to drop a reference to the disk's
queue. A call to blk_cleanup_queue() just prior to that will have
also dropped a reference to the queue.

The problem is that the reference dropped by put_disk() is assumed
to have been taken by add_disk(). Our code has error paths that can
occur after the disk and its queue are initialized, but before the
call to add_disk(), and in those paths we won't have that extra
reference.

The fix is easy though. In rbd_free_disk() we're already checking
the disk's GENHD_FL_UP flag. That flag is an indication that
add_disk() has been called, so just call blk_cleanup_queue()
conditional on that flag being set.

Signed-off-by: Alex Elder <elder@inktank.com>