block: Move bdev_unhash_inode() after invalidate_partition()

BugLink: http://bugs.launchpad.net/bugs/1659111

Move bdev_unhash_inode() after invalidate_partition() as
invalidate_partition() looks up bdev and it cannot find the right bdev
inode after bdev_unhash_inode() is called. Thus invalidate_partition()
would not invalidate page cache of the previously used bdev. Also use
part_devt() when calling bdev_unhash_inode() instead of manually
creating the device number.
Tested-by: Lekshmi Pillai <lekshmicpillai@in.ibm.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@fb.com>
(cherry picked from commit 4b8c861a)
Signed-off-by: Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Acked-by: Seth Forshee <seth.forshee@canonical.com>
Acked-by: Brad Figg <brad.figg@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>

block/genhd.c

@@ -646,9 +646,8 @@ void del_gendisk(struct gendisk *disk)
 	disk_part_iter_init(&piter, disk,
 			     DISK_PITER_INCL_EMPTY | DISK_PITER_REVERSE);
 	while ((part = disk_part_iter_next(&piter))) {
-		bdev_unhash_inode(MKDEV(disk->major,
-					disk->first_minor + part->partno));
 		invalidate_partition(disk, part->partno);
+		bdev_unhash_inode(part_devt(part));
 		delete_partition(disk, part->partno);
 	}
 	disk_part_iter_exit(&piter);