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From:   "Rafael J. Wysocki" <rjw@rjwysocki.net>
To:     Bo Yan <byan@nvidia.com>
Cc:     viresh.kumar@linaro.org, sgurrappadi@nvidia.com,
        linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] cpufreq: skip cpufreq resume if it's not suspended
Date:   Wed, 24 Jan 2018 03:02:09 +0100
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On Tuesday, January 23, 2018 10:57:55 PM CET Bo Yan wrote:
> cpufreq_resume can be called even without preceding cpufreq_suspend.
> This can happen in following scenario:
> 
>     suspend_devices_and_enter
>        --> dpm_suspend_start
>           --> dpm_prepare
>               --> device_prepare : this function errors out
>           --> dpm_suspend: this is skipped due to dpm_prepare failure
>                            this means cpufreq_suspend is skipped over
>        --> goto Recover_platform, due to previous error
>        --> goto Resume_devices
>        --> dpm_resume_end
>            --> dpm_resume
>                --> cpufreq_resume
> 
> In case schedutil is used as frequency governor, cpufreq_resume will
> eventually call sugov_start, which does following:
> 
>     memset(sg_cpu, 0, sizeof(*sg_cpu));
>     ....
> 
> This effectively erases function pointer for frequency update, causing
> crash later on. The function pointer would have been set correctly if
> subsequent cpufreq_add_update_util_hook runs successfully, but that
> function returns earlier because cpufreq_suspend was not called:
> 
>     if (WARN_ON(per_cpu(cpufreq_update_util_data, cpu)))
> 		return;
> 
> Ideally, suspend should succeed, then things will be fine. But even
> in case of suspend failure, system should not crash.
> 
> The fix is to check cpufreq_suspended first, if it's false, that means
> cpufreq_suspend was not called in the first place, so do not resume
> cpufreq.
> 
> Signed-off-by: Bo Yan <byan@nvidia.com>
> ---
>  drivers/cpufreq/cpufreq.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index 41d148af7748..95b1c4afe14e 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -1680,6 +1680,10 @@ void cpufreq_resume(void)
>  	if (!cpufreq_driver)
>  		return;
>  
> +	if (unlikely(!cpufreq_suspended)) {
> +		pr_warn("%s: resume after failing suspend\n", __func__);
> +		return;
> +	}
>  	cpufreq_suspended = false;
>  
>  	if (!has_target() && !cpufreq_driver->resume)
> 

Good catch, but rather than doing this it would be better to avoid
calling cpufreq_resume() at all if cpufreq_suspend() has not been called.

Thanks,
Rafael