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Date: Sun, 19 Oct 2008 00:03:19 +0400
From: Cyrill Gorcunov <gorcunov@gmail.com>
To: Ingo Molnar <mingo@elte.hu>, Peter Zijlstra <peterz@infradead.org>
Cc: LKML <linux-kernel@vger.kernel.org>
Subject: CFS related question
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Hi Ingo, Peter,

I just curious, look we have the following

static struct sched_entity *pick_next_entity(struct cfs_rq *cfs_rq)
{
	struct sched_entity *se = NULL;

	if (first_fair(cfs_rq)) {
		se = __pick_next_entity(cfs_rq);
		se = pick_next(cfs_rq, se);
		set_next_entity(cfs_rq, se);
	}

	return se;
}

which I presume may return NULL so the following piece
could fail

static struct task_struct *pick_next_task_fair(struct rq *rq)
{
	struct task_struct *p;
	struct cfs_rq *cfs_rq = &rq->cfs;
	struct sched_entity *se;

	if (unlikely(!cfs_rq->nr_running))
		return NULL;

	do {
-->		se = pick_next_entity(cfs_rq);
--> OOPs	cfs_rq = group_cfs_rq(se);
	} while (cfs_rq);

	p = task_of(se);
	hrtick_start_fair(rq, p);

	return p;
}

Did I miss something? Or it comepletely can NOT happen?

		- Cyrill -