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Subject: Re: [PATCH 4/5] sched/deadline: Cleanup on_dl_rq() handling
To:     Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@kernel.org>,
        Juri Lelli <juri.lelli@redhat.com>
Cc:     Luca Abeni <luca.abeni@santannapisa.it>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Qais Yousef <Qais.Yousef@arm.com>, linux-kernel@vger.kernel.org
References: <20190726082756.5525-1-dietmar.eggemann@arm.com>
 <20190726082756.5525-5-dietmar.eggemann@arm.com>
From:   Valentin Schneider <valentin.schneider@arm.com>
Message-ID: <0f460dba-4677-00de-59a2-5cd31ffe6e4b@arm.com>
Date:   Fri, 26 Jul 2019 09:37:29 +0100
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On 26/07/2019 09:27, 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@arm.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;
> -

Any idea why a similar error leads to a BUG_ON() in the enqueue path but
only a silent return on the dequeue path? I would expect the handling to be
almost identical.