linux-kernel - Re: [PATCH v2] sched: pick_next_rt_entity(): checked list

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Message-ID: <CAEih1qXHjrbMnMKa=DKVNTYbFoBKLi0ji+usRMgjLFqmvrbVeA@mail.gmail.com>
Date:   Mon, 6 Feb 2023 23:38:09 +0100
From:   Pietro Borrello <borrello@...g.uniroma1.it>
To:     Phil Auld <pauld@...hat.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        Dmitry Adamushko <dmitry.adamushko@...il.com>,
        Cristiano Giuffrida <c.giuffrida@...nl>,
        "Bos, H.J." <h.j.bos@...nl>, Jakob Koschel <jkl820.git@...il.com>,
        Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] sched: pick_next_rt_entity(): checked list_entry

On Mon, 6 Feb 2023 at 17:57, Phil Auld <pauld@...hat.com> wrote:
>
> 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@...g.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.
>

Thanks for the feedback.
Fixed in v3: https://lore.kernel.org/all/20230128-list-entry-null-check-sched-v3-1-b1a71bd1ac6b@diag.uniroma1.it/T/#u

Best regards,
Pietro