linux-kernel - Re: [PATCH RESEND 1/2] sched/deadline: Fix wrong cpudl_find() in check_preempt_equal

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Message-ID: <CADcy93WbR50KdiFj_nchyzmDBHoEqK7NSLiEoi=N0zTfg4VKvg@mail.gmail.com>
Date:	Fri, 27 Mar 2015 22:37:33 +0800
From:	Xunlei Pang <pang.xunlei@...aro.org>
To:	Juri Lelli <juri.lelli@...il.com>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH RESEND 1/2] sched/deadline: Fix wrong cpudl_find() in check_preempt_equal_dl()

Ping Juri

> From: Xunlei Pang <pang.xunlei@...aro.org>
>
> In check_preempt_equal_dl(), cpudl_find() is called with a NULL
> later_mask, thus cpudl_find() here doesn't check cpudl::free_cpus
> at all.
>
> This patch takles this issue by always passing a non-NULL later_mask
> to cpudl_find(), thereby fixing this issue.
>
> Signed-off-by: Xunlei Pang <pang.xunlei@...aro.org>
> ---
>  kernel/sched/cpudeadline.c |  8 +++-----
>  kernel/sched/deadline.c    | 15 +++++++++++----
>  2 files changed, 14 insertions(+), 9 deletions(-)
>
> diff --git a/kernel/sched/cpudeadline.c b/kernel/sched/cpudeadline.c
> index c6acb07..f331fcf 100644
> --- a/kernel/sched/cpudeadline.c
> +++ b/kernel/sched/cpudeadline.c
> @@ -97,7 +97,7 @@ static inline int cpudl_maximum(struct cpudl *cp)
>   * cpudl_find - find the best (later-dl) CPU in the system
>   * @cp: the cpudl max-heap context
>   * @p: the task
> - * @later_mask: a mask to fill in with the selected CPUs (or NULL)
> + * @later_mask: a mask to fill in with the selected CPUs (not NULL)
>   *
>   * Returns: int - best CPU (heap maximum if suitable)
>   */
> @@ -107,15 +107,13 @@ int cpudl_find(struct cpudl *cp, struct task_struct *p,
>         int best_cpu = -1;
>         const struct sched_dl_entity *dl_se = &p->dl;
>
> -       if (later_mask &&
> -           cpumask_and(later_mask, cp->free_cpus, &p->cpus_allowed)) {
> +       if (cpumask_and(later_mask, cp->free_cpus, &p->cpus_allowed)) {
>                 best_cpu = cpumask_any(later_mask);
>                 goto out;
>         } else if (cpumask_test_cpu(cpudl_maximum(cp), &p->cpus_allowed) &&
>                         dl_time_before(dl_se->deadline, cp->elements[0].dl)) {
>                 best_cpu = cpudl_maximum(cp);
> -               if (later_mask)
> -                       cpumask_set_cpu(best_cpu, later_mask);
> +               cpumask_set_cpu(best_cpu, later_mask);
>         }
>
>  out:
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index 0a81a95..256099c 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -964,14 +964,23 @@ out:
>         return cpu;
>  }
>
> +static DEFINE_PER_CPU(cpumask_var_t, local_cpu_mask_dl);
> +
>  static void check_preempt_equal_dl(struct rq *rq, struct task_struct *p)
>  {
> +       struct cpumask *later_mask =
> +                       this_cpu_cpumask_var_ptr(local_cpu_mask_dl);
> +
> +       /* Make sure the mask is initialized first */
> +       if (unlikely(!later_mask))
> +               return;
> +
>         /*
>          * Current can't be migrated, useless to reschedule,
>          * let's hope p can move out.
>          */
>         if (rq->curr->nr_cpus_allowed == 1 ||
> -           cpudl_find(&rq->rd->cpudl, rq->curr, NULL) == -1)
> +           cpudl_find(&rq->rd->cpudl, rq->curr, later_mask) == -1)
>                 return;
>
>         /*
> @@ -979,7 +988,7 @@ static void check_preempt_equal_dl(struct rq *rq, struct task_struct *p)
>          * see if it is pushed or pulled somewhere else.
>          */
>         if (p->nr_cpus_allowed != 1 &&
> -           cpudl_find(&rq->rd->cpudl, p, NULL) != -1)
> +           cpudl_find(&rq->rd->cpudl, p, later_mask) != -1)
>                 return;
>
>         resched_curr(rq);
> @@ -1173,8 +1182,6 @@ next_node:
>         return NULL;
>  }
>
> -static DEFINE_PER_CPU(cpumask_var_t, local_cpu_mask_dl);
> -
>  static int find_later_rq(struct task_struct *task)
>  {
>         struct sched_domain *sd;
> --
> 1.9.1
>
>
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