linux-kernel - Re: [RFCv6 PATCH 03/10] sched: scheduler-driven cpu frequency selection

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Date:	Tue, 2 Feb 2016 01:10:19 +0800
From:	Ricky Liang <jcliang@...omium.org>
To:	Steve Muckle <steve.muckle@...aro.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	open list <linux-kernel@...r.kernel.org>,
	linux-pm@...r.kernel.org,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Morten Rasmussen <morten.rasmussen@....com>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Juri Lelli <Juri.Lelli@....com>,
	Patrick Bellasi <patrick.bellasi@....com>,
	Michael Turquette <mturquette@...libre.com>
Subject: Re: [RFCv6 PATCH 03/10] sched: scheduler-driven cpu frequency selection

Hi Steve,

On Wed, Dec 9, 2015 at 2:19 PM, Steve Muckle <steve.muckle@...aro.org> wrote:

[snip...]

> +static int cpufreq_sched_policy_init(struct cpufreq_policy *policy)
> +{
> +       struct gov_data *gd;
> +       int cpu;
> +
> +       for_each_cpu(cpu, policy->cpus)
> +               memset(&per_cpu(cpu_sched_capacity_reqs, cpu), 0,
> +                      sizeof(struct sched_capacity_reqs));
> +
> +       gd = kzalloc(sizeof(*gd), GFP_KERNEL);
> +       if (!gd)
> +               return -ENOMEM;
> +
> +       gd->throttle_nsec = policy->cpuinfo.transition_latency ?
> +                           policy->cpuinfo.transition_latency :
> +                           THROTTLE_NSEC;
> +       pr_debug("%s: throttle threshold = %u [ns]\n",
> +                 __func__, gd->throttle_nsec);
> +
> +       if (cpufreq_driver_is_slow()) {
> +               cpufreq_driver_slow = true;
> +               gd->task = kthread_create(cpufreq_sched_thread, policy,
> +                                         "kschedfreq:%d",
> +                                         cpumask_first(policy->related_cpus));
> +               if (IS_ERR_OR_NULL(gd->task)) {
> +                       pr_err("%s: failed to create kschedfreq thread\n",
> +                              __func__);
> +                       goto err;
> +               }
> +               get_task_struct(gd->task);
> +               kthread_bind_mask(gd->task, policy->related_cpus);
> +               wake_up_process(gd->task);
> +               init_irq_work(&gd->irq_work, cpufreq_sched_irq_work);
> +       }
> +
> +       policy->governor_data = gd;

This should be moved before if(cpufreq_driver_is_slow()) {...}. I've
seen NULL pointer deference at boot in cpufreq_sched_thread() when it
tried to run sched_setscheduler_nocheck(gd->task, SCHED_FIFO, &param).

> +       set_sched_freq();
> +
> +       return 0;
> +
> +err:

And probably also set policy->governor_data to NULL here.

> +       kfree(gd);
> +       return -ENOMEM;
> +}

[snip...]

Best,
Ricky