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From:   "Rafael J. Wysocki" <rjw@rjwysocki.net>
To:     Prateek Sood <prsood@codeaurora.org>
Cc:     viresh.kumar@linaro.org, linux-pm@vger.kernel.org,
        linux-kernel@vger.kernel.org, gkohli@codeaurora.org,
        linux-arm-msm@vger.kernel.org
Subject: Re: Query related to usage of cpufreq_suspend() & cpufreq_resume
Date:   Fri, 02 Feb 2018 12:48:13 +0100
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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