linux-kernel - Re: [PATCH] thermal: core: Allow orderly

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Date:   Wed, 12 Apr 2017 22:06:40 -0700
From:   Eduardo Valentin <edubezval@...il.com>
To:     Keerthy <j-keerthy@...com>
Cc:     rui.zhang@...el.com, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-omap@...r.kernel.org,
        nm@...com, t-kristo@...com
Subject: Re: [PATCH] thermal: core: Allow orderly_poweroff to be called only
 once

Hey,

On Wed, Apr 12, 2017 at 02:42:12PM +0530, Keerthy wrote:
> thermal_zone_device_check --> thermal_zone_device_update -->
> handle_thermal_trip --> handle_critical_trips --> orderly_poweroff
> 
> The above sequence happens every 250/500 mS based on the configuration.
> The orderly_poweroff function is getting called every 250/500 mS.
> With a full fledged file system it takes at least 5-10 Seconds to
> power off gracefully.
> 
> In that period due to the thermal_zone_device_check triggering
> periodically the thermal work queues bombard with
> orderly_poweroff calls multiple times eventually leading to
> failures in gracefully powering off the system.
> 
> Make sure that orderly_poweroff is called only once.
> 
> Fixes: 0c01ebbfd3caf1d ("Thermal: Remove throttling logic out of thermal_sys.c")

Why? how the above commit introduced this issue?

> Reported-by: Nishanth Menon <nm@...com>
> Signed-off-by: Keerthy <j-keerthy@...com>
> ---
>  drivers/thermal/thermal_core.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/thermal/thermal_core.c b/drivers/thermal/thermal_core.c
> index 11f0675..4e68ce0 100644
> --- a/drivers/thermal/thermal_core.c
> +++ b/drivers/thermal/thermal_core.c
> @@ -326,6 +326,7 @@ static void handle_critical_trips(struct thermal_zone_device *tz,
>  				  int trip, enum thermal_trip_type trip_type)
>  {
>  	int trip_temp;
> +	static bool power_off_triggered;
>  

I am not convinced this change does what you say it does..

>  	tz->ops->get_trip_temp(tz, trip, &trip_temp);
>  
> @@ -338,11 +339,12 @@ static void handle_critical_trips(struct thermal_zone_device *tz,
>  	if (tz->ops->notify)
>  		tz->ops->notify(tz, trip, trip_type);
>  
> -	if (trip_type == THERMAL_TRIP_CRITICAL) {
> +	if (trip_type == THERMAL_TRIP_CRITICAL && !power_off_triggered) {
>  		dev_emerg(&tz->device,
>  			  "critical temperature reached(%d C),shutting down\n",
>  			  tz->temperature / 1000);
>  		orderly_poweroff(true);

Imagine you have two zones about to enter critical path. thermal zone 0
first gets into critical, and at this line (btween orderly_poweroff()
and you set your flag), it gets preempted. Then thermal zone 1 also
enters the critical path, then happens to be scheduled, you essentially
end up still calling orderly_poweroff() twice, which is what this patch
is supposed to avoid.

You better simply use a lock to serialize code execution.

BR,

> +		power_off_triggered = true;
>  	}
>  }
>  
> -- 
> 1.9.1
> 

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