Philippe Gerum wrote:
> Gilles Chanteperdrix wrote:
> > Philippe Gerum wrote:
> > > prio(task1) > prio(task2)
> > >
> > > 1. task1 grabs a resource
> > > 2. task1 sleeps for some time
> > > 3. task2 blocks requesting the resource
> > > 4. task1 wakes up from the sleep and releases the resource to task2
> > > 5. task1 wants the resource back immediately and calls
> > > xnsynch_sleep_on() since the ownership has been transferred to task2
> > > since step 4.
> > > 6a. old way: task1 would block and task2 would run anyway, with a PIP
> > > boost, blocking task1 until the resource is released
> > > 6b. new way: task1 steals the resource previously granted to task2
> > > directly from xnsynch_sleep_on(), but doing so, nobody downstream has
> > > had a chance to update any skin-specific data, such as an additional
> > > "owner" field.
> > Posix skin mutexes work the new way without calling xnsynch_sleep_on, so
> > probably need fixing.
> I don't see any additional information maintained by the skin, aside of
> the sem->count field, so that should be ok as it is. Is there anything
> else recorded for tracking the current ownership of a sem-mutex object?
The mutex->count field is unconditionnaly set to 0 and task2 woken up
when task1 releases the mutex, so that when task1 want the mutex again,
it will appear as free, and task1 will get it without calling
xnsynch_sleep_on, task2 will eventually wakeup spuriously or not
depending on whether the mutex is free. So, setting the count to 0 when
waking up seems wrong.
In a nut shell, the posix skin should be changed to use the new feature
instead of implementing its own behaviour.
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