[PATCH] sync blockdevs on the final close only

From: davej@codemonkey.org.uk

We currently run sync_blockdev() on every close of a blockdev.  This patch
arranges for the sync to happen only on the final close.

fs/block_dev.c

@@ -653,15 +653,16 @@ int blkdev_put(struct block_device *bdev, int kind)
 	struct gendisk *disk = bdev->bd_disk;
 
 	down(&bdev->bd_sem);
-	switch (kind) {
-	case BDEV_FILE:
-	case BDEV_FS:
-		sync_blockdev(bd_inode->i_bdev);
-		break;
-	}
 	lock_kernel();
-	if (!--bdev->bd_openers)
+	if (!--bdev->bd_openers) {
+		switch (kind) {
+		case BDEV_FILE:
+		case BDEV_FS:
+			sync_blockdev(bd_inode->i_bdev);
+			break;
+		}
 		kill_bdev(bdev);
+	}
 	if (bdev->bd_contains == bdev) {
 		if (disk->fops->release)
 			ret = disk->fops->release(bd_inode, NULL);