linux-kernel - Re: [RFC 0/12][PATCH] SCHED_DEADLINE: fork and terminate task logic

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Date:	Wed, 13 Jan 2010 17:15:11 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Raistlin <raistlin@...ux.it>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	michael trimarchi <michael@...dence.eu.com>,
	Fabio Checconi <fabio@...dalf.sssup.it>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Dhaval Giani <dhaval.giani@...il.com>,
	Johan Eker <johan.eker@...csson.com>,
	"p.faure" <p.faure@...tech.ch>,
	Chris Friesen <cfriesen@...tel.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Henrik Austad <henrik@...tad.us>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Darren Hart <darren@...art.com>,
	Sven-Thorsten Dietrich <sven@...bigcorporation.com>,
	Claudio Scordino <claudio@...dence.eu.com>,
	Tommaso Cucinotta <tommaso.cucinotta@...up.it>,
	"giuseppe.lipari" <giuseppe.lipari@...up.it>,
	Juri Lelli <juri.lelli@...il.com>
Subject: Re: [RFC 0/12][PATCH] SCHED_DEADLINE: fork and terminate task logic

On Wed, 2010-01-13 at 12:11 +0100, Raistlin wrote:

> > > +       } else if (rt_prio(p->prio))
> > > +               p->sched_class = &rt_sched_class;
> > > +       else
> > >                 p->sched_class = &fair_sched_class;
> > >  
> > >  #ifdef CONFIG_SMP
> > > @@ -2744,6 +2756,10 @@ static void finish_task_switch(struct rq *rq, struct task_struct *prev)
> > >         if (mm)
> > >                 mmdrop(mm);
> > >         if (unlikely(prev_state == TASK_DEAD)) {
> > > +               /* a deadline task is dying: stop the bandwidth timer */
> > > +               if (deadline_task(prev))
> > > +                       hrtimer_cancel(&prev->dl.dl_timer);
> > > +
> > >                 /*
> > >                  * Remove function-return probe instances associated with this
> > >                  * task and put them back on the free list. 
> > 
> > Shouldn't this be done in the ->dequeue_task() callback?
> >
> Not sure of this snippet... Actually, it is one of the most disturbing
> piece of code of this whole scheduler. :-(
> 
> The reason why it is here is that I think it is needed to call
> hrtimer_cancel() _without_ holding the rq->lock, is that correct?

I think we can nest the hrtimer base lock inside the rq->lock these
days, so it should be safe to call while holding it, anyway, lockdep
will quickly tell you if you try ;-)

> It is 

Is that a stmt or an unfinished sentence?

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