block: ublk_drv: mark device as LIVE before adding disk

IO can be started before add_disk() returns, such as reading parititon table,
then the monitor work should work for making forward progress.

So mark device as LIVE before adding disk, meantime change to
DEAD if add_disk() fails.

Fixed: 71f28f3 ("ublk_drv: add io_uring based userspace block driver")
Reviewed-by: Ziyang Zhang <ZiyangZhang@linux.alibaba.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20230318141231.55562-1-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: Ming Lei

drivers/block/ublk_drv.c

@@ -1602,17 +1602,18 @@ static int ublk_ctrl_start_dev(struct ublk_device *ub, struct io_uring_cmd *cmd)
 		set_bit(GD_SUPPRESS_PART_SCAN, &disk->state);
 
 	get_device(&ub->cdev_dev);
+	ub->dev_info.state = UBLK_S_DEV_LIVE;
 	ret = add_disk(disk);
 	if (ret) {
 		/*
 		 * Has to drop the reference since ->free_disk won't be
 		 * called in case of add_disk failure.
 		 */
+		ub->dev_info.state = UBLK_S_DEV_DEAD;
 		ublk_put_device(ub);
 		goto out_put_disk;
 	}
 	set_bit(UB_STATE_USED, &ub->state);
-	ub->dev_info.state = UBLK_S_DEV_LIVE;
 out_put_disk:
 	if (ret)
 		put_disk(disk);