block: fix blk_integrity_register to use template's interval_exp if not 0

When registering an integrity profile: if the template's interval_exp is
not 0 use it, otherwise use the ilog2() of logical block size of the
provided gendisk.

This fixes a long-standing DM linear target bug where it cannot pass
integrity data to the underlying device if its logical block size
conflicts with the underlying device's logical block size.

Cc: stable@vger.kernel.org
Reported-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Acked-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

block/blk-integrity.c

@@ -412,7 +412,8 @@ void blk_integrity_register(struct gendisk *disk, struct blk_integrity *template
 
 	bi->flags = BLK_INTEGRITY_VERIFY | BLK_INTEGRITY_GENERATE |
 		template->flags;
-	bi->interval_exp = ilog2(queue_logical_block_size(disk->queue));
+	bi->interval_exp = template->interval_exp ? :
+		ilog2(queue_logical_block_size(disk->queue));
 	bi->profile = template->profile ? template->profile : &nop_profile;
 	bi->tuple_size = template->tuple_size;
 	bi->tag_size = template->tag_size;