linux-kernel - Re: [PATCH v3] sched: pick_next_rt_entity(): check list

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Date:   Tue, 7 Feb 2023 10:11:17 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Pietro Borrello <borrello@...g.uniroma1.it>
Cc:     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>,
        Phil Auld <pauld@...hat.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 v3] sched: pick_next_rt_entity(): check list_entry

On Mon, 06 Feb 2023 22:33:54 +0000
Pietro Borrello <borrello@...g.uniroma1.it> wrote:

> Commit 326587b84078 ("sched: fix goto retry in pick_next_task_rt()")
> removed any path which could make pick_next_rt_entity() return NULL.
> However, BUG_ON(!rt_se) in _pick_next_task_rt() (the only caller of
> pick_next_rt_entity()) still checks the error condition, which can
> never happen, since list_entry() never returns NULL.
> Remove the BUG_ON check, and instead emit a warning in the only
> possible error condition here: the queue being empty which should
> never happen.
> 
> Fixes: 326587b84078 ("sched: fix goto retry in pick_next_task_rt()")
> Signed-off-by: Pietro Borrello <borrello@...g.uniroma1.it>
> ---
> Changes in v3:
> - return NULL if the list is empty
> - Link to v2: https://lore.kernel.org/r/20230128-list-entry-null-check-sched-v2-1-d8e010cce91b@diag.uniroma1.it
> 
> Changes in v2:
> - pick_next_rt_entity(): emit warning instead of crashing
> - Link to v1: https://lore.kernel.org/r/20230128-list-entry-null-check-sched-v1-1-c93085ee0055@diag.uniroma1.it
> ---
>  kernel/sched/rt.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index ed2a47e4ddae..0a11f44adee5 100644

Reviewed-by: Steven Rostedt (Google) <rostedt@...dmis.org>

-- Steve