Date:   Mon, 6 Feb 2023 11:57:20 -0500
From:   Phil Auld <pauld@redhat.com>
To:     Steven Rostedt <rostedt@goodmis.org>
Cc:     Pietro Borrello <borrello@diag.uniroma1.it>,
        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: <Y+ExcOoHOzSctvue@lorien.usersys.redhat.com>
References: <20230128-list-entry-null-check-sched-v2-1-d8e010cce91b@diag.uniroma1.it>
 <20230206112342.223d2c29@rorschach.local.home>
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On Mon, Feb 06, 2023 at 11:23:42AM -0500 Steven Rostedt wrote:
> 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;

I think that's better than taking a digger in one of the subsequent macros.


Cheers,
Phil


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


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