Re: [PATCH v2 2/3] mutex: add support for reservation style locks, v2

Peter Zijlstra
2013-04-04T16:49:31Z

On Thu, 2013-04-04 at 15:31 +0200, Daniel Vetter wrote:
> We've discussed this approach of using (rt-prio, age) instead of just
> age
> to determine the the "oldness" of a task for deadlock-breaking with
> -EAGAIN. The problem is that through PI boosting or normal rt-prio
> changes
> while tasks are trying to acquire ww_mutexes you can create acyclic
> loops
> in the blocked-on graph of ww_mutexes after the fact and so cause
> deadlocks. So we've convinced ourselves that this approche doesn't
> work.

Could you pretty please draw me a picture, I'm having trouble seeing
what you mean.

AFAICT as long as you boost Y while its the lock owner things should
work out, no?