The articles code for mutex_lock is this mutex_lock(unsigned int mutex) { while (!cmpxchg(&mutex, UNLOCKED, LOCKED)) futex(&mutex, FUTEX_WAIT, LO

The articles code for mutex_lock is this mutex_lock(unsigned int mutex) { while (!cmpxchg(&mutex, UNLOCKED, LOCKED)) futex(&mutex, FUTEX_WAIT, LOCKED); } Now consider what happens if someone calls it volatile unsigned int my_mutex = UNLOCKED; mutex_lock(my_mutex); ... mutex_unlock(my_mutex); my_mutex is copied into the mutex parameter. The mutex parameter is updated to locked. mutex_lock exits, which destroys the mutex variable. my_mutex still has the variable UNLOCKED.