Messages in this thread | | | Subject | Re: [Patch v3 3/6] cpufreq: qcom-cpufreq-hw: Add dcvs interrupt support | From | Thara Gopinath <> | Date | Mon, 12 Jul 2021 21:18:25 -0400 |
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On 7/12/21 12:41 AM, Viresh Kumar wrote: > On 09-07-21, 11:37, Thara Gopinath wrote: >> On 7/9/21 2:46 AM, Viresh Kumar wrote: >>>> @@ -389,6 +503,10 @@ static int qcom_cpufreq_hw_cpu_exit(struct cpufreq_policy *policy) >>>> dev_pm_opp_remove_all_dynamic(cpu_dev); >>>> dev_pm_opp_of_cpumask_remove_table(policy->related_cpus); >>>> + if (data->lmh_dcvs_irq > 0) { >>>> + devm_free_irq(cpu_dev, data->lmh_dcvs_irq, data); >>> >>> Why using devm variants here and while requesting the irq ? > > Missed this one ?
Yep. I just replied to Bjorn's email on this. I will move to non devm version.
> >>> >>>> + cancel_delayed_work_sync(&data->lmh_dcvs_poll_work); >>>> + } >>> >>> Please move this to qcom_cpufreq_hw_lmh_exit() or something. >> >> Ok. >> >>> >>> Now with sequence of disabling interrupt, etc, I see a potential >>> problem. >>> >>> CPU0 CPU1 >>> >>> qcom_cpufreq_hw_cpu_exit() >>> -> devm_free_irq(); >>> qcom_lmh_dcvs_poll() >>> -> qcom_lmh_dcvs_notify() >>> -> enable_irq() >>> >>> -> cancel_delayed_work_sync(); >>> >>> >>> What will happen if enable_irq() gets called after freeing the irq ? >>> Not sure, but it looks like you will hit this then from manage.c: >>> >>> WARN(!desc->irq_data.chip, KERN_ERR "enable_irq before >>> setup/request_irq: irq %u\n", irq)) >>> >>> ? >>> >>> You got a chicken n egg problem :) >> >> Yes indeed! But also it is a very rare chicken and egg problem. >> The scenario here is that the cpus are busy and running load causing a >> thermal overrun and lmh is engaged. At the same time for this issue to be >> hit the cpu is trying to exit/disable cpufreq. > > Yes, it is a very specific case but it needs to be resolved anyway. You don't > want to get this ever :) > >> Calling >> cancel_delayed_work_sync first could solve this issue, right ? >> cancel_delayed_work_sync guarantees the work not to be pending even if >> it requeues itself on return. So once the delayed work is cancelled, the >> interrupts can be safely disabled. Thoughts ? > > I don't think even that would provide such guarantees to you here, as there is > a chance the work gets queued again because of an interrupt that triggers right > after you cancel the work. > > The basic way of solving such issues is that once you cancel something, you need > to guarantee that it doesn't get triggered again, no matter what. > > The problem here I see is with your design itself, both delayed work and irq can > enable each other, so no matter which one you disable first, won't be > sufficient. You need to fix that design somehow.
So I really need the interrupt to fire and then the timer to kick in and take up the monitoring. I can think of introducing a variable is_disabled which is updated and read under a spinlock. qcom_cpufreq_hw_cpu_exit can hold the spinlock and set is_disabled to true prior to cancelling the work queue or disabling the interrupt. Before re-enabling the interrupt or re-queuing the work in qcom_lmh_dcvs_notify, is_disabled can be read and checked.
But does this problem not exist in target_index , fast_switch etc also ? One cpu can be disabling and the other one can be updating the target right?
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-- Warm Regards Thara (She/Her/Hers)
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