Joseph,
Patch is not accepted by upstream and below is the comment from one of the reviewer,
There seems to be problem with this patch. bdi_unregister() is also called by blk_cleanup_queue(), and both that and del_gendisk() may be called by cleanup_mapped_device(). This results in a panic when bdi_unregister() is called for the second time.
Joseph,
Patch is not accepted by upstream and below is the comment from one of the reviewer,
There seems to be problem with this patch. bdi_unregister() is also called by blk_cleanup_ queue() , and both that and del_gendisk() may be called by cleanup_ mapped_ device( ). This results in a panic when bdi_unregister() is called for the second time.