linux-kernel - Re: Bug in scheduler when using rt

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Date:	Wed, 19 Jan 2011 15:13:19 +0200
From:	Onkalo Samu <samu.p.onkalo@...ia.com>
To:	ext Peter Zijlstra <peterz@...radead.org>
Cc:	Yong Zhang <yong.zhang0@...il.com>, mingo@...e.hu,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	tglx <tglx@...utronix.de>
Subject: Re: Bug in scheduler when using rt_mutex

On Wed, 2011-01-19 at 14:58 +0200, Onkalo Samu wrote:
> On Wed, 2011-01-19 at 12:30 +0100, ext Peter Zijlstra wrote:
> > On Wed, 2011-01-19 at 11:38 +0100, Peter Zijlstra wrote:
> > 
> > > Hrm, I think the to bit is not needed with the from thing in place, the
> > > enqueue from _setprio will already have added min_vruntime
> > 
> > 
> > Would lead to something like this:
> > 
> 
> Doesn't work in my case.

When the task is sleeping rt_mutex_setprio
doesn't call check_class_changed since the task is not 
in queue at that moment I think.

> 
> > ---
> > Index: linux-2.6/kernel/sched.c
> > ===================================================================
> > --- linux-2.6.orig/kernel/sched.c
> > +++ linux-2.6/kernel/sched.c
> > @@ -8108,6 +8108,8 @@ EXPORT_SYMBOL(__might_sleep);
> >  #ifdef CONFIG_MAGIC_SYSRQ
> >  static void normalize_task(struct rq *rq, struct task_struct *p)
> >  {
> > +	struct sched_class *prev_class = p->sched_class;
> > +	int old_prio = p->prio;
> >  	int on_rq;
> >  
> >  	on_rq = p->se.on_rq;
> > @@ -8118,6 +8120,8 @@ static void normalize_task(struct rq *rq
> >  		activate_task(rq, p, 0);
> >  		resched_task(rq->curr);
> >  	}
> > +
> > +	check_class_changed(rq, p, prev_class, old_prio, task_current(rq, p));
> >  }
> >  
> >  void normalize_rt_tasks(void)
> > Index: linux-2.6/kernel/sched_fair.c
> > ===================================================================
> > --- linux-2.6.orig/kernel/sched_fair.c
> > +++ linux-2.6/kernel/sched_fair.c
> > @@ -4066,11 +4066,30 @@ static void prio_changed_fair(struct rq
> >  		check_preempt_curr(rq, p, 0);
> >  }
> >  
> > +static void
> > +switched_from_fair(struct rq *rq, struct task_struct *p, int running)
> > +{
> > +	struct sched_entity *se = &p->se;
> > +	struct cfs_rq *cfs_rq = cfs_rq_of(se);
> > +
> > +	/*
> > +	 * Ensure the task's vruntime is normalized, so that when its
> > +	 * switched back to the fair class the enqueue_entity(.flags=0) will
> > +	 * do the right thing.
> > +	 *
> > +	 * If it was on_rq, then the dequeue_entity(.flags=0) will already
> > +	 * have normalized the vruntime, if it was !on_rq, then only when
> > +	 * the task is sleeping will it still have non-normalized vruntime.
> > +	 */
> > +	if (!se->on_rq && p->state != TASK_RUNNING)
> > +		se->vruntime -= cfs_rq->min_vruntime;
> > +}
> > +
> >  /*
> >   * We switched to the sched_fair class.
> >   */
> > -static void switched_to_fair(struct rq *rq, struct task_struct *p,
> > -			     int running)
> > +static void
> > +switched_to_fair(struct rq *rq, struct task_struct *p, int running)
> >  {
> >  	/*
> >  	 * We were most likely switched from sched_rt, so
> > @@ -4163,6 +4182,7 @@ static const struct sched_class fair_sch
> >  	.task_fork		= task_fork_fair,
> >  
> >  	.prio_changed		= prio_changed_fair,
> > +	.switched_from		= switched_from_fair,
> >  	.switched_to		= switched_to_fair,
> >  
> >  	.get_rr_interval	= get_rr_interval_fair,
> > 
> 
> 


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