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

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Date:	Wed, 19 Jan 2011 06:40:57 +0100
From:	Mike Galbraith <efault@....de>
To:	Yong Zhang <yong.zhang0@...il.com>
Cc:	Peter Zijlstra <peterz@...radead.org>, samu.p.onkalo@...ia.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 12:35 +0800, Yong Zhang wrote:

> cfs_rq->curr != se is always true.

If that were always true, we'd illegally enqueue a running task.

        if (running)
                p->sched_class->set_curr_task(rq);
                ==> set_curr_task_fair(rq);
                ==>      struct sched_entity *se = &rq->curr->se;
                ==>      set_next_entity(cfs_rq_of(se), se);
                ==>          cfs_rq->curr = se;
                (prevents running entity from being enqueued below)
        if (on_rq) {
                enqueue_task(rq, p, oldprio < prio ? ENQUEUE_HEAD : 0);

                check_class_changed(rq, p, prev_class, oldprio, running);
        }

	-Mike

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