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

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