block: unhash the whole device inode earlier

Unhash the whole device inode early in del_gendisk.  This allows to
remove the first GENHD_FL_UP check in the open path as we simply
won't find a just removed inode.  The second non-racy check after
taking open_mutex is still kept.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20210722075402.983367-4-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/genhd.c

@@ -585,6 +585,7 @@ void del_gendisk(struct gendisk *disk)
 	disk_del_events(disk);
 
 	mutex_lock(&disk->open_mutex);
+	remove_inode_hash(disk->part0->bd_inode);
 	disk->flags &= ~GENHD_FL_UP;
 	blk_drop_partitions(disk);
 	mutex_unlock(&disk->open_mutex);
@@ -592,12 +593,6 @@ void del_gendisk(struct gendisk *disk)
 	fsync_bdev(disk->part0);
 	__invalidate_device(disk->part0, true);
 
-	/*
-	 * Unhash the bdev inode for this device so that it can't be looked
-	 * up any more even if openers still hold references to it.
-	 */
-	remove_inode_hash(disk->part0->bd_inode);
-
 	set_capacity(disk, 0);
 
 	if (!(disk->flags & GENHD_FL_HIDDEN)) {

fs/block_dev.c

@@ -1340,7 +1340,7 @@ struct block_device *blkdev_get_no_open(dev_t dev)
 	disk = bdev->bd_disk;
 	if (!kobject_get_unless_zero(&disk_to_dev(disk)->kobj))
 		goto bdput;
-	if ((disk->flags & (GENHD_FL_UP | GENHD_FL_HIDDEN)) != GENHD_FL_UP)
+	if (disk->flags & GENHD_FL_HIDDEN)
 		goto put_disk;
 	if (!try_module_get(bdev->bd_disk->fops->owner))
 		goto put_disk;