The idea behind mutexes is to only allow one thread access to a section of memory at any one time. If one thread locks the mutex, any other lock attempts will block until the first one unlocks. However, how is this implemented? To lock itself, the mutex has to set a bit somewhere that says that it is locked. But what if the second mutex is reading at the same time the first is writing. Worse, what if they both lock the mutex at the same time? The mutex would succumb to the same problem it is meant to prevent.
How do mutexes really work?