Stopping an epoll runloop with kthread_stop - linux-kernel

Question

I'm using epoll in a kernel module.
I'm creating a kthread on module_init, and I want to stop it on module_exit.
However, this thread is always almost waiting in epoll_wait.
In my exit function, how can I stop the created thread even if it's waiting in epoll_wait?
This is my attempt, but every now and then it hangs, I assume because the interrupt doesn't get to the thread before kthread_stop does.
struct task_struct *thread;
bool should_stop = false;
static int __init init(void) {
thread = kthread_run(run, NULL, "hora");
return 0;
}
static void __exit exit(void) {
l("end");
should_stop = true;
force_sig(SIGUSR1, thread);
l("kthread_stop");
kthread_stop(thread);
l("ended");
}
int run(void *data) {
...
while (true) {
int nfd = epoll_wait(epfd, events, MAX_EVENTS, -1);
l("got event");
if (should_stop) {
l("should_stop");
break;
}
...
}
...
l("closed");
set_current_state(TASK_INTERRUPTIBLE);
while (!kthread_should_stop()) {
schedule();
set_current_state(TASK_INTERRUPTIBLE);
}
set_current_state(TASK_RUNNING);
l("exiting");
return 0;
}
The output is:
end
kthread_stop
got event
should_stop
closed
exiting
ended
I've looked into eventfd as an alternative to sending a signal, but it's quite a bit of work (only a couple of eventfd functions are exported) and I don't know for sure whether it'll solve this.
Any insights and help much appreciated.