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

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Message-ID: <20190726092005.GO25636@localhost.localdomain>
Date:   Fri, 26 Jul 2019 11:20:05 +0200
From:   Juri Lelli <juri.lelli@...hat.com>
To:     Valentin Schneider <valentin.schneider@....com>
Cc:     Dietmar Eggemann <dietmar.eggemann@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Luca Abeni <luca.abeni@...tannapisa.it>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Qais Yousef <Qais.Yousef@....com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/5] sched/deadline: Cleanup on_dl_rq() handling

Hi,

On 26/07/19 09:37, Valentin Schneider wrote:
> 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@....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.
>  

Task could have already been dequeued by update_curr_dl()->throttle
called by dequeue_task_dl() before calling __dequeue_task_dl().

Thanks,

Juri