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

Hi Steve,

On Wed, Dec 9, 2015 at 2:19 PM, Steve Muckle [off-list ref] 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