static int dm_call_pr(struct block_device *bdev, iterate_devices_callout_fn fn,
		      void *data)
{
	struct mapped_device *md = bdev->bd_disk->private_data;
	struct dm_table *table;
	struct dm_target *ti;
	int ret = -ENOTTY, srcu_idx;

	table = dm_get_live_table(md, &srcu_idx);
	if (!table || !dm_table_get_size(table))
		goto out;

	/* We only support devices that have a single target */
	if (dm_table_get_num_targets(table) != 1)
		goto out;
	ti = dm_table_get_target(table, 0);

	ret = -EINVAL;
	if (!ti->type->iterate_devices)
		goto out;

	ret = ti->type->iterate_devices(ti, fn, data);
out:
	dm_put_live_table(md, srcu_idx);
	return ret;
}

The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.