Re: [PATCH 1/3] sched/deadline: clear dl_entity params when setscheduling to different class

[Wanpeng Li]

Hi Juri,

ä 9/19/14, 5:22 PM, Juri Lelli åé:
> When a task is using SCHED_DEADLINE and the user setschedules it to a different
> class its sched_dl_entity static parameters are not cleaned up. This causes a
> bug if the user sets it back to SCHED_DEADLINE with the same parameters again.
> The problem resides in the check we perform at the very beginning of
> dl_overflow():
>
> 	if (new_bw == p->dl.dl_bw)
> 		return 0;
>
> This condition is met in the case depicted above, so the function returns and
> dl_b->total_bw is not updated (the p->dl.dl_bw is not added to it). After this,

As you know there is no static parameter clear before this patch, so if 
p->dl.dl_bw will decrease from dl_b->total_bw when the user setschedules 
to a different class instead of dl?

Regards,
Wanpeng Li

> admission control is broken.
>
> This patch fixes the thing, properly clearing static parameters for a task
> that ceases to use SCHED_DEADLINE.
>
> Reported-by: Daniele Alessandrelli <daniele.alessandrelli@xxxxxxxxx>
> Reported-by: Daniel Wagner <daniel.wagner@xxxxxxxxxxxx>
> Reported-by: Vincent Legout <vincent@xxxxxxxxxxx>
> Tested-by: Luca Abeni <luca.abeni@xxxxxxxx>
> Signed-off-by: Juri Lelli <juri.lelli@xxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Juri Lelli <juri.lelli@xxxxxxxxx>
> Cc: Dario Faggioli <raistlin@xxxxxxxx>
> Cc: Michael Trimarchi <michael@xxxxxxxxxxxxxxxxxxxx>
> Cc: Fabio Checconi <fchecconi@xxxxxxxxx>
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> ---
>   kernel/sched/core.c     | 19 +++++++++++++++----
>   kernel/sched/deadline.c |  2 ++
>   kernel/sched/sched.h    |  3 +++
>   3 files changed, 20 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index ec1a286..581a429 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -1776,6 +1776,20 @@ int wake_up_state(struct task_struct *p, unsigned int state)
>   }
>   
>   /*
> + * This function clears the sched_dl_entity static params.
> + */
> +void __dl_clear_params(struct task_struct *p)
> +{
> +	struct sched_dl_entity *dl_se = &p->dl;
> +
> +	dl_se->dl_runtime = 0;
> +	dl_se->dl_deadline = 0;
> +	dl_se->dl_period = 0;
> +	dl_se->flags = 0;
> +	dl_se->dl_bw = 0;
> +}
> +
> +/*
>    * Perform scheduler related setup for a newly forked process p.
>    * p is forked by current.
>    *
> @@ -1799,10 +1813,7 @@ static void __sched_fork(unsigned long clone_flags, struct task_struct *p)
>   
>   	RB_CLEAR_NODE(&p->dl.rb_node);
>   	hrtimer_init(&p->dl.dl_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
> -	p->dl.dl_runtime = p->dl.runtime = 0;
> -	p->dl.dl_deadline = p->dl.deadline = 0;
> -	p->dl.dl_period = 0;
> -	p->dl.flags = 0;
> +	__dl_clear_params(p);
>   
>   	INIT_LIST_HEAD(&p->rt.run_list);
>   
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index 255ce13..4a51b14 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -1569,6 +1569,8 @@ static void switched_from_dl(struct rq *rq, struct task_struct *p)
>   	if (hrtimer_active(&p->dl.dl_timer) && !dl_policy(p->policy))
>   		hrtimer_try_to_cancel(&p->dl.dl_timer);
>   
> +	__dl_clear_params(p);
> +
>   #ifdef CONFIG_SMP
>   	/*
>   	 * Since this might be the only -deadline task on the rq,
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index 579712f..4890484 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -126,6 +126,9 @@ struct rt_bandwidth {
>   	u64			rt_runtime;
>   	struct hrtimer		rt_period_timer;
>   };
> +
> +void __dl_clear_params(struct task_struct *p);
> +
>   /*
>    * To keep the bandwidth of -deadline tasks and groups under control
>    * we need some place where:

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