linux-kernel - Re: [PATCH 4/5] sched/deadline: Cleanup on_dl

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Date:   Mon, 29 Jul 2019 18:49:32 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Dietmar Eggemann <dietmar.eggemann@....com>
Cc:     Ingo Molnar <mingo@...nel.org>, Juri Lelli <juri.lelli@...hat.com>,
        Luca Abeni <luca.abeni@...tannapisa.it>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <Valentin.Schneider@....com>,
        Qais Yousef <Qais.Yousef@....com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/5] sched/deadline: Cleanup on_dl_rq() handling

On Fri, Jul 26, 2019 at 09:27:55AM +0100, Dietmar Eggemann wrote:
> Remove BUG_ON() in __enqueue_dl_entity() since there is already one in
> enqueue_dl_entity().
> 
> Move the check that the dl_se is not on the dl_rq from
> __dequeue_dl_entity() to dequeue_dl_entity() to align with the enqueue
> side and use the on_dl_rq() helper function.
> 
> Signed-off-by: Dietmar Eggemann <dietmar.eggemann@....com>
> ---
>  kernel/sched/deadline.c | 8 +++-----
>  1 file changed, 3 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index 1fa005f79307..a9cb52ceb761 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -1407,8 +1407,6 @@ static void __enqueue_dl_entity(struct sched_dl_entity *dl_se)
>  	struct sched_dl_entity *entry;
>  	int leftmost = 1;
>  
> -	BUG_ON(!RB_EMPTY_NODE(&dl_se->rb_node));
> -
>  	while (*link) {
>  		parent = *link;
>  		entry = rb_entry(parent, struct sched_dl_entity, rb_node);
> @@ -1430,9 +1428,6 @@ static void __dequeue_dl_entity(struct sched_dl_entity *dl_se)
>  {
>  	struct dl_rq *dl_rq = dl_rq_of_se(dl_se);
>  
> -	if (RB_EMPTY_NODE(&dl_se->rb_node))
> -		return;
> -
>  	rb_erase_cached(&dl_se->rb_node, &dl_rq->root);
>  	RB_CLEAR_NODE(&dl_se->rb_node);
>  
> @@ -1466,6 +1461,9 @@ enqueue_dl_entity(struct sched_dl_entity *dl_se,
>  
>  static void dequeue_dl_entity(struct sched_dl_entity *dl_se)
>  {
> +	if (!on_dl_rq(dl_se))
> +		return;

Why allow double dequeue instead of WARN?

> +
>  	__dequeue_dl_entity(dl_se);
>  }
>  
> -- 
> 2.17.1
>