linux-kernel - Re: [PATCH] sched/deadline: fix switching to -deadline

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Date:   Fri, 21 Apr 2017 10:39:26 +0100
From:   Juri Lelli <juri.lelli@....com>
To:     luca abeni <luca.abeni@...tannapisa.it>
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Claudio Scordino <claudio@...dence.eu.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Tommaso Cucinotta <tommaso.cucinotta@...up.it>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Mathieu Poirier <mathieu.poirier@...aro.org>
Subject: Re: [PATCH] sched/deadline: fix switching to -deadline

Hi Luca,

On 20/04/17 21:30, Luca Abeni wrote:
> From: Luca Abeni <luca.abeni@...tannapisa.it>
> 
> When switching to -deadline, if the scheduling deadline of a task is
> in the past then switched_to_dl() calls setup_new_entity() to properly
> initialize the scheduling deadline and runtime.
> 
> The problem is that the task is enqueued _before_ having its parameters
> initialized by setup_new_entity(), and this can cause problems.
> For example, a task with its out-of-date deadline in the past will
> potentially be enqueued as the highest priority one; however, its
> adjusted deadline may not be the earliest one.
> 
> This patch fixes the problem by initializing the task's parameters before
> enqueuing it.
> 
> Signed-off-by: Luca Abeni <luca.abeni@...tannapisa.it>
> Reviewed-by: Daniel Bristot de Oliveira <bristot@...hat.com>
> ---
>  kernel/sched/deadline.c | 12 ++++--------
>  1 file changed, 4 insertions(+), 8 deletions(-)
> 
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index a2ce590..ec53d24 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -950,6 +950,10 @@ enqueue_dl_entity(struct sched_dl_entity *dl_se,
>  		update_dl_entity(dl_se, pi_se);
>  	else if (flags & ENQUEUE_REPLENISH)
>  		replenish_dl_entity(dl_se, pi_se);
> +	else if ((flags & ENQUEUE_RESTORE) &&

Not sure I understand how this works. AFAICT we are doing
__sched_setscheduler() when we want to catch the case of a new dl_entity
(SCHED_{OTHER,FIFO} -> SCHED_DEADLINE}, but queue_flags (which are
passed to enqueue_task()) don't seem to have ENQUEUE_RESTORE set?

Thanks,

- Juri