block: call blk_register_queue earlier in device_add_disk

Ensure that all the sysfs bits are set up before bdev_add is called,
as that will make the upcomding error handling much easier.  However
this means the call to disk_update_readahead has to be split as that
requires a bdi.  Also remove various sanity checks that don't make
sense now that blk_register_queue only has a single caller.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20210818144542.19305-7-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-sysfs.c

@@ -856,15 +856,6 @@ int blk_register_queue(struct gendisk *disk)
 	struct device *dev = disk_to_dev(disk);
 	struct request_queue *q = disk->queue;
 
-	if (WARN_ON(!q))
-		return -ENXIO;
-
-	WARN_ONCE(blk_queue_registered(q),
-		  "%s is registering an already registered queue\n",
-		  kobject_name(&dev->kobj));
-
-	disk_update_readahead(disk);
-
 	ret = blk_trace_init_sysfs(dev);
 	if (ret)
 		return ret;

block/genhd.c

@@ -508,6 +508,8 @@ void device_add_disk(struct device *parent, struct gendisk *disk,
 		disk->slave_dir = NULL;
 	}
 
+	blk_register_queue(disk);
+
 	if (disk->flags & GENHD_FL_HIDDEN) {
 		/*
 		 * Don't let hidden disks show up in /proc/partitions,
@@ -537,8 +539,7 @@ void device_add_disk(struct device *parent, struct gendisk *disk,
 		disk_uevent(disk, KOBJ_ADD);
 	}
 
-	blk_register_queue(disk);
-
+	disk_update_readahead(disk);
 	disk_add_events(disk);
 }
 EXPORT_SYMBOL(device_add_disk);