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Subject: Re: Bug in scheduler when using rt_mutex
From: Mike Galbraith <efault@gmx.de>
To: Yong Zhang <yong.zhang0@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>, samu.p.onkalo@nokia.com,
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Date: Wed, 19 Jan 2011 06:40:57 +0100
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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