Re: [Patch v4 3/6] cpufreq: qcom-cpufreq-hw: Add dcvs interrupt support

[Thara Gopinath]

On 7/27/21 11:50 PM, Viresh Kumar wrote:
> On 27-07-21, 11:25, Thara Gopinath wrote:
> > +static void qcom_lmh_dcvs_notify(struct qcom_cpufreq_data *data)
> > +{
>
> > +	/* In the unlikely case cpufreq is de-registered do not enable polling or h/w interrupt */
> > +
> > +	spin_lock(&data->throttle_lock);
> > +	if (data->cancel_throttle) {
> > +		spin_unlock(&data->throttle_lock);
> > +		return;
> > +	}
> > +	spin_unlock(&data->throttle_lock);
> > +
> > +	/*
> > +	 * If h/w throttled frequency is higher than what cpufreq has requested for, stop
> > +	 * polling and switch back to interrupt mechanism
> > +	 */
> > +
> > +	if (throttled_freq >= qcom_cpufreq_hw_get(cpumask_first(policy->cpus)))
> > +		/* Clear the existing interrupts and enable it back */
> > +		enable_irq(data->throttle_irq);
> > +	else
> > +		mod_delayed_work(system_highpri_wq, &data->throttle_work,
> > +				 msecs_to_jiffies(10));
> > +}
>
> > +static void qcom_cpufreq_hw_lmh_exit(struct qcom_cpufreq_data *data)
> > +{
> > +	if (data->throttle_irq <= 0)
> > +		return;
> > +
> > +	spin_lock(&data->throttle_lock);
> > +	data->cancel_throttle = true;
> > +	spin_unlock(&data->throttle_lock);
> > +	cancel_delayed_work_sync(&data->throttle_work);
> > +	free_irq(data->throttle_irq, data);
> > +}
>
> Lets see if we can still make it break :)
>
> CPU0                                            CPU1
>
> qcom_lmh_dcvs_notify()                          qcom_cpufreq_hw_lmh_exit()
>
> spin_unlock()
>                                                  spin_lock(),
>                                                  cancel_throttle = true
>                                                  spin_unlock()
>
>                                                  cancel_delayed_work_sync()
> mod_delayed_work()
>                                                  free_irq()
>                                                  kfree(data)
> qcom_lmh_dcvs_poll()
> Uses data.
>
>
> Sorry, locking is fun :)

Ha! I was too lazy to write this down! So how about I make this a mutex 
and put mod_delayed_work() inside the lock. So it will be something like 
below

qcom_lmh_dcvs_notify()			qcom_cpufreq_hw_lmh_exit()

mutex_lock()				mutex_lock()
  if (data->cancel_throttle) {		cancel_throttle = true
	mutex_unlock()			mutex_unlock()
	return				cancel_delayed_work_sync()
  }					free_irq()
  enable_irq() / mod_delayed_work()
mutex_unlock()

I will let you break it!

>

--
Warm Regards
Thara (She/Her/Hers)