On Tue, 2007-01-09 at 10:09 +0100, Oliver Neukum wrote: > Am Dienstag, 9. Januar 2007 10:02 schrieb Peter Zijlstra:
> > Its a fundamental property of a mutex, not a shortcoming. A mutex has an > > owner, the one that takes and releases the resource. This allows things > > such as Priority Inheritance to boost owners. > > > > 'fixing' this takes away much of what a mutex is. > > > > That said, it seems some folks really want this to happen, weird as it > > may be. I'm not sure if all these cases are because of wrong designs. A > > possible extension to the mutex interface might be something like this: > > > > mutex_pass_owner(struct task_struct *task); > > > > which would be an atomic unlock/lock pair where the current task > > releases the resource and the indicated task gains it. However it must > > be understood that from the POV of 'current' this should be treated as > > an unlock action. > > This won't help if I want to release from an interrupt handler or tasklet. Then that shouldn't use a mutex. A mutex is for "mutual exclusion", and not "shared exclusion". Peter is right that the fundamental property of a mutex, is that it is for a single thread. And it should never be released by a separate thread than the one that grabbed it. A semaphore can be used as a mutex, but not the other way around. I wouldn't even recommend doing the mutex_pass_owner(). To do so, the process calling this must be the owner, and the parameter must be a thread waiting on the mutex. If it is not, then that could introduce some really nasty races and bugs. The mutex_unlock_dont_warn_if_a_different_task_did_it() is also a bad idea. -- Steve - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
