timerfd-panic.c

#include <pthread.h>
#include <stdio.h>
#include <stdint.h>
#include <sys/timerfd.h>
#include <unistd.h>

void* thread_main(void* arg) {
    int fd = *((int*)arg);

    printf("Waiting for the timer to fire.\n");
    uint64_t count;
    read(fd, &count, sizeof(count));

    printf("Closing the timerfd on another thread. PREPARE FOR THE KERNEL PANIC!\n");
    close(fd);

    printf("Wow it survived. We're still alive...\n");
    return NULL;
}

int main() {
    int fd = timerfd_create(CLOCK_REALTIME, 0);
    if (fd == -1) {
        perror("timerfd_create");
        return 1;
    }

    struct itimerspec tim = {{1, 0}, {1, 0}};
    if (timerfd_settime(fd, 0, &tim, NULL) != 0) {
        perror("timerfd_settime");
        return 1;
    }
    printf("Created a timerfd on the main thread: %d\n", fd);

    pthread_t thr;
    if (pthread_create(&thr, NULL, thread_main, &fd) != 0) {
        perror("pthread_create");
        return 1;
    }

    pthread_join(thr, NULL);
    return 0;
}