md: suspend i/o during runtime blk_integrity_unregister

Synchronize pending i/o against a change in the integrity profile to
avoid the possibility of spurious integrity errors.  Given linear_add()
is suspending the mddev before manipulating the mddev, do the same for
the other personalities.

Acked-by: NeilBrown <neilb@suse.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

drivers/md/md.c

@@ -1994,6 +1994,7 @@ void md_integrity_add_rdev(struct md_rdev *rdev, struct mddev *mddev)
 	if (bi_rdev && blk_integrity_compare(mddev->gendisk,
 					     rdev->bdev->bd_disk) >= 0)
 		return;
+	WARN_ON_ONCE(!mddev->suspended);
 	printk(KERN_NOTICE "disabling data integrity on %s\n", mdname(mddev));
 	blk_integrity_unregister(mddev->gendisk);
 }