Date:   Mon, 6 Feb 2023 11:23:42 -0500
From:   Steven Rostedt <rostedt@goodmis.org>
To:     Pietro Borrello <borrello@diag.uniroma1.it>
Cc:     Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Valentin Schneider <vschneid@redhat.com>,
        Dmitry Adamushko <dmitry.adamushko@gmail.com>,
        Cristiano Giuffrida <c.giuffrida@vu.nl>,
        "Bos, H.J." <h.j.bos@vu.nl>, Jakob Koschel <jkl820.git@gmail.com>,
        Ingo Molnar <mingo@elte.hu>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] sched: pick_next_rt_entity(): checked list_entry
Message-ID: <20230206112342.223d2c29@rorschach.local.home>
In-Reply-To: <20230128-list-entry-null-check-sched-v2-1-d8e010cce91b@diag.uniroma1.it>
References: <20230128-list-entry-null-check-sched-v2-1-d8e010cce91b@diag.uniroma1.it>
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On Tue, 31 Jan 2023 13:01:16 +0000
Pietro Borrello <borrello@diag.uniroma1.it> wrote:

> index ed2a47e4ddae..c024529d8416 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -1777,6 +1777,7 @@ static struct sched_rt_entity *pick_next_rt_entity(struct rt_rq *rt_rq)
>  	BUG_ON(idx >= MAX_RT_PRIO);
>  
>  	queue = array->queue + idx;
> +	SCHED_WARN_ON(list_empty(queue));

I wonder if we should make this:

	if (SCHED_WARN_ON(list_empty(queue)))
		return NULL;

>  	next = list_entry(queue->next, struct sched_rt_entity, run_list);
>  
>  	return next;
> @@ -1789,7 +1790,6 @@ static struct task_struct *_pick_next_task_rt(struct rq *rq)
>  
>  	do {
>  		rt_se = pick_next_rt_entity(rt_rq);
> -		BUG_ON(!rt_se);

		if (unlikely(!rt_se))
			return NULL;

-- Steve

>  		rt_rq = group_rt_rq(rt_se);
>  	} while (rt_rq);
>