http://lwn.net/Articles/167034/ This is a special feed containing comments posted to the individual LWN article titled "The mutex API". hourly 2 http://lwn.net/Articles/167355/rss 2006-01-12T09:41:39+00:00 simlo <I> Note that mutex_unlock() cannot be called from interrupt context. This restriction appears to have more to do with keeping mutexes from ever being used as completions than a fundamental restriction caused by the mutex design itself.</I> <p> If you could it would not be a mutex but a semaphore! A mutex can only be unlocked by the owner - which must be a task. But when you turn off the debug code, Ingo's mutex is indeed just a binary semaphore. <p> At computer science we were indeed told to use binary semaphores as mutual exclusion locks. But it is a bad advice. The semantics is very different. To help debugging and make the code more understandable it is really a good idea to use seperate types for completion type semaphores and mutex and to enforce the mutex semantics. On real-time systems you must use a mutex with some kind of priority inversion prevention (priority inheritance or priority ceiling). Therefore it is essential not to mix up mutex with completions on that kind of systems.<p> Furthermore: When a mutex can't be touched from interrupts, you don't have to disable interrupts while performing mutex operations.