ublk_drv: cancel device even though disk isn't up

Each ublk queue is started before adding disk, we have to cancel queues in
ublk_stop_dev() so that ubq daemon can be exited, otherwise DEL_DEV command
may hang forever.

Also avoid to cancel queues two times by checking if queue is ready,
otherwise use-after-free on io_uring may be triggered because ublk_stop_dev
is called by ublk_remove() too.

Fixes: 71f28f3 ("ublk_drv: add io_uring based userspace block driver")
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20220730092750.1118167-2-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: Ming Lei

drivers/block/ublk_drv.c

@@ -788,16 +788,27 @@ static void ublk_daemon_monitor_work(struct work_struct *work)
 				UBLK_DAEMON_MONITOR_PERIOD);
 }
 
+static inline bool ublk_queue_ready(struct ublk_queue *ubq)
+{
+	return ubq->nr_io_ready == ubq->q_depth;
+}
+
 static void ublk_cancel_queue(struct ublk_queue *ubq)
 {
 	int i;
 
+	if (!ublk_queue_ready(ubq))
+		return;
+
 	for (i = 0; i < ubq->q_depth; i++) {
 		struct ublk_io *io = &ubq->ios[i];
 
 		if (io->flags & UBLK_IO_FLAG_ACTIVE)
 			io_uring_cmd_done(io->cmd, UBLK_IO_RES_ABORT, 0);
 	}
+
+	/* all io commands are canceled */
+	ubq->nr_io_ready = 0;
 }
 
 /* Cancel all pending commands, must be called after del_gendisk() returns */
@@ -818,19 +829,14 @@ static void ublk_stop_dev(struct ublk_device *ub)
 	del_gendisk(ub->ub_disk);
 	ub->dev_info.state = UBLK_S_DEV_DEAD;
 	ub->dev_info.ublksrv_pid = -1;
-	ublk_cancel_dev(ub);
 	put_disk(ub->ub_disk);
 	ub->ub_disk = NULL;
  unlock:
+	ublk_cancel_dev(ub);
 	mutex_unlock(&ub->mutex);
 	cancel_delayed_work_sync(&ub->monitor_work);
 }
 
-static inline bool ublk_queue_ready(struct ublk_queue *ubq)
-{
-	return ubq->nr_io_ready == ubq->q_depth;
-}
-
 /* device can only be started after all IOs are ready */
 static void ublk_mark_io_ready(struct ublk_device *ub, struct ublk_queue *ubq)
 {