Deal with page == NULL in the btrfs_unplug_io_fn

	return ret;

}

/*

 * this unplugs every device on the box, and it is only used when page

 * is null

 */

static void __unplug_io_fn(struct backing_dev_info *bdi, struct page *page)

{

	struct list_head *cur;

	struct btrfs_device *device;

	struct btrfs_fs_info *info;

	info = (struct btrfs_fs_info *)bdi->unplug_io_data;

	list_for_each(cur, &info->fs_devices->devices) {

		device = list_entry(cur, struct btrfs_device, dev_list);

		bdi = blk_get_backing_dev_info(device->bdev);

		if (bdi->unplug_io_fn) {

			bdi->unplug_io_fn(bdi, page);

		}

	}

}

void btrfs_unplug_io_fn(struct backing_dev_info *bdi, struct page *page)

{

	struct inode *inode = page->mapping->host;

	struct inode *inode;

	struct extent_map_tree *em_tree;

	struct extent_map *em;

	u64 offset = page_offset(page);

	u64 offset;

	if (!page) {

		__unplug_io_fn(bdi, page);

		return;

	}

	inode = page->mapping->host;

	offset = page_offset(page);

	em_tree = &BTRFS_I(inode)->extent_tree;

	spin_lock(&em_tree->lock);