block: Don't revalidate bdev of hidden gendisk

When hidden gendisk is revalidated, there's no point in revalidating
associated block device as there's none. We would thus just create new
bdev inode, report "detected capacity change from 0 to XXX" message and
evict the bdev inode again. Avoid this pointless dance and confusing
message in the kernel log.
Reviewed-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/block_dev.c

@@ -1406,20 +1406,27 @@ void check_disk_size_change(struct gendisk *disk, struct block_device *bdev,
  */
 int revalidate_disk(struct gendisk *disk)
 {
-	struct block_device *bdev;
 	int ret = 0;
 
 	if (disk->fops->revalidate_disk)
 		ret = disk->fops->revalidate_disk(disk);
-	bdev = bdget_disk(disk, 0);
-	if (!bdev)
-		return ret;
 
-	mutex_lock(&bdev->bd_mutex);
-	check_disk_size_change(disk, bdev, ret == 0);
-	bdev->bd_invalidated = 0;
-	mutex_unlock(&bdev->bd_mutex);
-	bdput(bdev);
+	/*
+	 * Hidden disks don't have associated bdev so there's no point in
+	 * revalidating it.
+	 */
+	if (!(disk->flags & GENHD_FL_HIDDEN)) {
+		struct block_device *bdev = bdget_disk(disk, 0);
+
+		if (!bdev)
+			return ret;
+
+		mutex_lock(&bdev->bd_mutex);
+		check_disk_size_change(disk, bdev, ret == 0);
+		bdev->bd_invalidated = 0;
+		mutex_unlock(&bdev->bd_mutex);
+		bdput(bdev);
+	}
 	return ret;
 }
 EXPORT_SYMBOL(revalidate_disk);