Prevent a possible race condition when _mutex_timeout fires just after the
mutex was locked but before the xtimer was removed
The flow
int xtimer_mutex_lock_timeout(mutex_t *mutex, uint64_t timeout) {
...
mutex_lock(mutex);
/* mutex locked */
/* _mutex_timeout fires and tries to remove thread from mutex queue */
/* DEBUG: simulate callback call between lock and remove */
xtimer_spin(xtimer_ticks_from_usec(timeout*2));
xtimer_remove(&t);
...
}
f3b13cf90c