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Subject: Re: Query related to usage of cpufreq_suspend() & cpufreq_resume
To:     "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc:     viresh.kumar@linaro.org, linux-pm@vger.kernel.org,
        linux-kernel@vger.kernel.org, gkohli@codeaurora.org,
        linux-arm-msm@vger.kernel.org
References: <e9d13871-184b-dee3-c45f-c6d19e671eea@codeaurora.org>
 <1949391.4ffJqIIJSQ@aspire.rjw.lan>
From:   Prateek Sood <prsood@codeaurora.org>
Message-ID: <7d50aeb5-cc2d-521b-2f31-5477e6e18f20@codeaurora.org>
Date:   Fri, 2 Feb 2018 18:23:32 +0530
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On 02/02/2018 05:18 PM, Rafael J. Wysocki wrote:
> On Friday, February 2, 2018 12:41:58 PM CET Prateek Sood wrote:
>> Hi Viresh,
>>
>> One scenario is there where a kernel panic is observed in
>> cpufreq during suspend/resume.
>>
>> pm_suspend()
>>   suspend_devices_and_enter()
>>     dpm_suspend_start()
>>       dpm_prepare() 
>>
>> Failure in dpm_prepare() happend with following dmesg:
>>
>> [ 3746.316062] PM: Device xyz not prepared for power transition: code -16
>> [ 3746.316071] PM: Some devices failed to suspend, or early wake event detected
>>
>>
>> pm_suspend()
>>   suspend_devices_and_enter()
>>     dpm_suspend_start()
>>       dpm_prepare() //failed
>>     dpm_resume_end()
>>       dpm_resume()
>>         cpufreq_resume()
>>           cpufreq_start_governor()
>>             sugov_start()
>>               cpufreq_add_update_util_hook()
>>
>> After failure in dpm_prepare(), dpm_resume() called
>> cpufreq_resume(). Corresponding cpufreq_suspend() was not
>> called due to failure of dpm_prepare(). 
>>
>> This resulted in WARN_ON(per_cpu(cpufreq_update_util_data, cpu))
>> in cpufreq_add_update_util_hook() and cpufreq_add_update_util_hook->func
>> being inconsistent state. It caused crash in scheduler.
>>
>> Following are some of the ways to mitigate this issue. Could
>> you please provide feedback on below two approaches or suugest
>> a better way to fix this problem.
>>
>> -----------------------8<------------------------------
>>
>> Co-developed-by: Gaurav Kohli <gkohli@codeaurora.org>
>> Signed-off-by: Gaurav Kohli <gkohli@codeaurora.org> 
>> Signed-off-by: Prateek Sood <prsood@codeaurora.org>
>>
>> diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
>> index 02a497e..732e5a2 100644
>> --- a/drivers/base/power/main.c
>> +++ b/drivers/base/power/main.c
>> @@ -1038,6 +1038,7 @@ void dpm_resume(pm_message_t state)
>>  {
>>         struct device *dev;
>>         ktime_t starttime = ktime_get();
>> +       bool valid_resume = false;
>>
>>         trace_suspend_resume(TPS("dpm_resume"), state.event, true);
>>         might_sleep();
>> @@ -1055,6 +1056,7 @@ void dpm_resume(pm_message_t state)
>>         }
>>
>>         while (!list_empty(&dpm_suspended_list)) {
>> +               valid_resume = true;
>>                 dev = to_device(dpm_suspended_list.next);
>>                 get_device(dev);
>>                 if (!is_async(dev)) {
>> @@ -1080,7 +1082,8 @@ void dpm_resume(pm_message_t state)
>>         async_synchronize_full();
>>         dpm_show_time(starttime, state, 0, NULL);
>>
>> -       cpufreq_resume();
>> +       if (valid_resume)
>> +               cpufreq_resume();
>>         trace_suspend_resume(TPS("dpm_resume"), state.event, false);
>>  }
>>
>> --------------------8<--------------------------------------
>>
>> Signed-off-by: Prateek Sood <prsood@codeaurora.org>
>>
>> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
>> index 421f318..439eab8 100644
>> --- a/drivers/cpufreq/cpufreq.c
>> +++ b/drivers/cpufreq/cpufreq.c
>> @@ -1648,7 +1648,7 @@ void cpufreq_suspend(void)
>>  {
>>         struct cpufreq_policy *policy;
>>
>> -       if (!cpufreq_driver)
>> +       if (!cpufreq_driver || cpufreq_suspended)
>>                 return;
>>
>>         if (!has_target() && !cpufreq_driver->suspend)
>> @@ -1683,7 +1683,7 @@ void cpufreq_resume(void)
>>         struct cpufreq_policy *policy;
>>         int ret;
>>
>> -       if (!cpufreq_driver)
>> +       if (!cpufreq_driver || !cpufreq_suspended)
>>                 return;
>>
>>         cpufreq_suspended = false;
> 
> Since we have cpufreq_suspended already, the second one is better.
> 
> Thanks,
> Rafael
> 

Thanks Rafael for the inputs, I will send a formal patch.


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