Re: [PATCH RT v2] Fix a lockup in wait_for_completion() and friends

From: Sebastian Andrzej Siewior
Date: Tue May 14 2019 - 11:27:11 EST

On 2019-05-14 13:35:38 [+0200], Peter Zijlstra wrote:
> On Tue, May 14, 2019 at 11:12:19AM +0200, Sebastian Andrzej Siewior wrote:
> > On 2019-05-14 10:43:56 [+0200], Peter Zijlstra wrote:
> > > Now.. that will fix it, but I think it is also wrong.
> > >
> > > The problem being that it violates FIFO, something that might be more
> > > important on -RT than elsewhere.
> >
> > Wouldn't -RT be more about waking the task with the highest priority
> > instead the one that waited the longest?
> Possibly, but that's a far larger patch. Also, even with that
> completions do not avoid inversions and thus don't really make nice RT
> primitives anyway.

See. So it does not really matter if a particular waiter ends up at the
end of the queue.
Anyway, I don't really think we need this but if you want it, let me add
What about the other question I had regarding completion_done()?