Is there a way, to receive data in a kernel module without using a callback function?

Question

I am currently writing a Linux kernel module, where I have to send requests to a user-space application out of a callback function.

So what I need in my module is something like this:

int callback_function () {
   ...
   send_request_to_app();
   receive_answer();
   ...
} 

I tried using generic netlink combined with wait_queues somewhat like this:

int response = 0;
DECLARE_WAIT_QUEUE_HEAD(wait_queue);

static int nl_recv_msg(struct sk_buff *skb, struct genl_info* info) {
   ...
   response = 1;
   wake_up_interruptible(&wait_queue);
   ...
}

int callback_function () {
   ...
   send_request_to_app();
   wait_event_interruptible(wait_queue, response);
   ...
} 

Similar to this question: How to send and receive messages from function other than registered callback function in Netlink socket?

This does not work for me, which I believe might be because of race conditions, since the callback_function is called frequently.

Is there another way to receive an answer without using another callback function or is there a different IPC method that solves this problem?

Edit: I am not trying to fix the code above. I am just looking for other methods/ideas.