long keyctl_revoke_key(key_serial_t id)
{
	key_ref_t key_ref;
	long ret;

	key_ref = lookup_user_key(id, 0, KEY_NEED_WRITE);
	if (IS_ERR(key_ref)) {
		ret = PTR_ERR(key_ref);
		if (ret != -EACCES)
			goto error;
		key_ref = lookup_user_key(id, 0, KEY_NEED_SETATTR);
		if (IS_ERR(key_ref)) {
			ret = PTR_ERR(key_ref);
			goto error;
		}
	}

	key_revoke(key_ref_to_ptr(key_ref));
	ret = 0;

	key_ref_put(key_ref);
error:
	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.