nbd: fix how we set bd_invalidated

bd_invalidated is kind of a pain wrt partitions as it really only
triggers the partition rescan if it is set after bd_ops->open() runs, so
setting it when we reset the device isn't useful.  We also sporadically
would still have partitions left over in some disconnect cases, so fix
this by always setting bd_invalidated on open if there's no
configuration or if we've had a disconnect action happen, that way the
partition table gets invalidated and rescanned properly.

Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/nbd.c

@@ -964,10 +964,6 @@ static void nbd_bdev_reset(struct block_device *bdev)
 	if (bdev->bd_openers > 1)
 		return;
 	bd_set_size(bdev, 0);
-	if (max_part > 0) {
-		blkdev_reread_part(bdev);
-		bdev->bd_invalidated = 1;
-	}
 }
 
 static void nbd_parse_flags(struct nbd_device *nbd)
@@ -1282,6 +1278,9 @@ static int nbd_open(struct block_device *bdev, fmode_t mode)
 		refcount_set(&nbd->config_refs, 1);
 		refcount_inc(&nbd->refs);
 		mutex_unlock(&nbd->config_lock);
+		bdev->bd_invalidated = 1;
+	} else if (nbd_disconnected(nbd->config)) {
+		bdev->bd_invalidated = 1;
 	}
 out:
 	mutex_unlock(&nbd_index_mutex);