[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);
+	lock_kernel();
+	if (!--bdev->bd_openers) {
 		switch (kind) {
 		case BDEV_FILE:
 		case BDEV_FS:
 			sync_blockdev(bd_inode->i_bdev);
 			break;
 		}
-	lock_kernel();
-	if (!--bdev->bd_openers)
 		kill_bdev(bdev);
+	}
 	if (bdev->bd_contains == bdev) {
 		if (disk->fops->release)
 			ret = disk->fops->release(bd_inode, NULL);