static int dm_blk_open(struct block_device *bdev, fmode_t mode)
{
	struct mapped_device *md;

	spin_lock(&_minor_lock);

	md = bdev->bd_disk->private_data;
	if (!md)
		goto out;

	if (test_bit(DMF_FREEING, &md->flags) ||
	    dm_deleting_md(md)) {
		md = NULL;
		goto out;
	}

	dm_get(md);
	atomic_inc(&md->open_count);
out:
	spin_unlock(&_minor_lock);

	return md ? 0 : -ENXIO;
}

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.