btrfs: Add check to avoid cleanup roots already in fs_info->dead_roots.

{

	u64 root_objectid = 0;

	struct btrfs_root *gang[8];

	int i;

	int ret;

	int i = 0;

	int err = 0;

	unsigned int ret = 0;

	int index;

	while (1) {

		index = srcu_read_lock(&fs_info->subvol_srcu);

		ret = radix_tree_gang_lookup(&fs_info->fs_roots_radix,

					     (void **)gang, root_objectid,

					     ARRAY_SIZE(gang));

		if (!ret)

		if (!ret) {

			srcu_read_unlock(&fs_info->subvol_srcu, index);

			break;

		}

		root_objectid = gang[ret - 1]->root_key.objectid + 1;

		for (i = 0; i < ret; i++) {

			int err;

			/* Avoid to grab roots in dead_roots */

			if (btrfs_root_refs(&gang[i]->root_item) == 0) {

				gang[i] = NULL;

				continue;

			}

			/* grab all the search result for later use */

			gang[i] = btrfs_grab_fs_root(gang[i]);

		}

		srcu_read_unlock(&fs_info->subvol_srcu, index);

		for (i = 0; i < ret; i++) {

			if (!gang[i])

				continue;

			root_objectid = gang[i]->root_key.objectid;

			err = btrfs_orphan_cleanup(gang[i]);

			if (err)

				return err;

				break;

			btrfs_put_fs_root(gang[i]);

		}

		root_objectid++;

	}

	return 0;

	/* release the uncleaned roots due to error */

	for (; i < ret; i++) {

		if (gang[i])

			btrfs_put_fs_root(gang[i]);

	}

	return err;

}

int btrfs_commit_super(struct btrfs_root *root)