Why does register_block release a bdev_inode instance at the end?

Hi, all: It has been known that all inodes that represent block devices are kept on the bdev pseudo-filesystem.And I thought that a bdev_inode instance is generated when the function of register_disk is called.But why does register_disk release a bdev_inode instance by calling blkdev_put at the end? BTW, my kernel is linux-2.6.32. RegardsRock Lee