deadlock on event_del_nolock_()

[legale]

aarch64 system kernel 5.4.164
libevent2 master fc9bfd2

I got flickering bug with deadlock on event_del_nolock_()

bt:

stuck on the libmosquito loop event EV_PERSIST callback.

This is callback

void mqtt_loop_callback(int fd, short event, void *arg) {
  // syslog2(LOG_INFO, "%s\n", __func__);
  int ret;

  struct timespec ts;
  ts.tv_sec = 0;
  ts.tv_nsec = 100000000; // 100ms

  int ret_misc = 0, ret_read = 0, ret_write = 0;

  fd_set read_fds, write_fds;

  FD_ZERO(&read_fds);
  FD_ZERO(&write_fds);

  FD_SET(fd, &read_fds);

  ret = locksafe_ms(mqtt_lock, 2000);
  if (ret){
    // syslog2(LOG_INFO, "%s END\n", __func__);
    return;
  }

  if (mosquitto_want_write(mosq)) {
    FD_SET(fd, &write_fds);
  }
  unlocksafe(mqtt_lock);

  ret = pselect(fd + 1, &read_fds, &write_fds, NULL, &ts, NULL);
  if (ret == -1) {
    syslog2(LOG_ERR, "pselect failed: returned: %d\n", ret);
    return;
  }

  ret = locksafe_ms(mqtt_lock, 1000);
  if (ret){
    // syslog2(LOG_INFO, "%s END\n", __func__);
    return;
  }

  if (FD_ISSET(fd, &read_fds)) {
    ret_read = mosquitto_loop_read(mosq, 1);
  }

  if (FD_ISSET(fd, &write_fds)) {
    ret_write = mosquitto_loop_write(mosq, 10);
  }

  mosquitto_loop_misc(mosq);
  unlocksafe(mqtt_lock);
  // syslog2(LOG_INFO, "%s END\n", __func__);
}

This is init function

static int setup_mqtt_loop_event(agent_config_t *ac) {
  syslog2(LOG_INFO, "%s\n", __func__);
  if (locksafe_ms(ac_events_lock, 1000)) return 1;
  if (locksafe_ms(mqtt_lock, 1000)) {
    unlocksafe(ac_lock);
    return 1;
  }

  ac->events.mqtt_loop.fd = mosquitto_socket(mosq);
  if (ac->events.mqtt_loop.fd == -1) {
    syslog2(LOG_ERR, "get mqtt fd failed\n");
    unlocksafe(mqtt_lock);
    unlocksafe(ac_events_lock);
    return 1;
  }

  if (event_initialized(&ac->events.mqtt_loop.ev)) {
    if (event_del(&ac->events.mqtt_loop.ev))
      syslog2(LOG_ERR, "unable to delete prev. mqtt_loop event\n");
  }

  event_assign(&ac->events.mqtt_loop.ev, ac->events.base, ac->events.mqtt_loop.fd, EV_READ | EV_WRITE | EV_PERSIST, mqtt_loop_callback, (void *)ac);
  event_add(&ac->events.mqtt_loop.ev, NULL);
  unlocksafe(mqtt_lock);
  unlocksafe(ac_events_lock);
  return 0;
}

[azat]

Looks like lines does not match.

Anyway it is hard to say something based on provided samples. But you can try to compile with TSan at least, and see what it will report about deadlocks. Also if you have threads, please make that you enabled pthread support (evthread_use_pthreads())