Re: [PATCH v2 2/2] thermal: core: Add a back up thermal shutdown mechanism

[Eduardo Valentin <edubezval@gmail.com>]

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Hey,

On Thu, Apr 13, 2017 at 01:32:36PM +0530, Keerthy wrote:
> orderly_poweroff is triggered when a graceful shutdown
> of system is desired. This may be used in many critical states of the
> kernel such as when subsystems detects conditions such as critical
> temperature conditions. However, in certain conditions in system
> boot up sequences like those in the middle of driver probes being
> initiated, userspace will be unable to power off the system in a clean
> manner and leaves the system in a critical state. In cases like these,
> the /sbin/poweroff will return success (having forked off to attempt
> powering off the system. However, the system overall will fail to
> completely poweroff (since other modules will be probed) and the system
> is still functional with no userspace (since that would have shut itself
> off).
> 
> However, there is no clean way of detecting such failure of userspace
> powering off the system. In such scenarios, it is necessary for a backup
> workqueue to be able to force a shutdown of the system when orderly
> shutdown is not successful after a configurable time period.

Thanks for keeping this thread up and fixing it. Some requests to this
patch too as follows.

> 
> Reported-by: Nishanth Menon <nm@ti.com>
> Signed-off-by: Keerthy <j-keerthy@ti.com>
> ---
> 
>   * Changed the comment style
>   * Added backup shutdown call before orderly_poweroff
> 
>  drivers/thermal/Kconfig        | 13 ++++++++++++
>  drivers/thermal/thermal_core.c | 47 ++++++++++++++++++++++++++++++++++++++++++

I think this change in expectation should probably be documented under
Documentation/ directory. Can you please patch thermal documentation
too?

>  2 files changed, 60 insertions(+)
> 
> diff --git a/drivers/thermal/Kconfig b/drivers/thermal/Kconfig
> index 9347401..971fd54 100644
> --- a/drivers/thermal/Kconfig
> +++ b/drivers/thermal/Kconfig
> @@ -15,6 +15,19 @@ menuconfig THERMAL
>  
>  if THERMAL
>  
> +config THERMAL_EMERGENCY_POWEROFF_DELAY_MS
> +	int "Emergency poweroff delay in milli-seconds"
> +	depends on THERMAL
> +	default 0
> +	help
> +	  The number of milliseconds to delay before emergency
> +	  poweroff kicks in. The delay should be carefully profiled
> +	  so as to give adequate time for orderly_poweroff. In case
> +	  of failure of an orderly_poweroff the emergency poweroff
> +	  kicks in after the delay has elapsed and shuts down the system.
> +
> +	  If set to 0 poweroff will happen immediately.
> +
>  config THERMAL_HWMON
>  	bool
>  	prompt "Expose thermal sensors as hwmon device"
> diff --git a/drivers/thermal/thermal_core.c b/drivers/thermal/thermal_core.c
> index 7462ae5..d60fa9e 100644
> --- a/drivers/thermal/thermal_core.c
> +++ b/drivers/thermal/thermal_core.c
> @@ -323,12 +323,54 @@ static void handle_non_critical_trips(struct thermal_zone_device *tz,
>  		       def_governor->throttle(tz, trip);
>  }
>  
> +/**
> + * emergency_poweroff_func - emergency poweroff work after a known delay
> + * @work: work_struct associated with the emergency poweroff function
> + *
> + * This function is called in very critical situations to force
> + * a kernel poweroff after a configurable timeout value.
> + */
> +static void emergency_poweroff_func(struct work_struct *work)
> +{
> +	/*
> +	 * We have reached here after the emergency thermal shutdown
> +	 * Waiting period has expired. This means orderly_poweroff has
> +	 * not been able to shut off the system for some reason.
> +	 * Try to shut down the system immediately using kernel_power_off
> +	 * if populated
> +	 */
> +	pr_warn("Attempting kernel_power_off\n");

This message needs to be specific to thermal (forced) shutdown.

> +	kernel_power_off();
> +
> +	/*
> +	 * Worst of the worst case trigger emergency restart
> +	 */
> +	pr_warn("kernel_power_off has failed! Attempting emergency_restart\n");

Same here..

also, I think if your system reached this point, we should probably be more
dramatic at the kernel log a scream louder, I would say a big farty WARN
to say the least. Or a crash.

> +	emergency_restart();
> +}
> +
> +static DECLARE_DELAYED_WORK(emergency_poweroff_work, emergency_poweroff_func);
> +
> +/**
> + * emergency_poweroff - Trigger an emergency system poweroff
> + *
> + * This may be called from any critical situation to trigger a system shutdown
> + * after a known period of time. By default the delay is 0 millisecond
> + */
> +void thermal_emergency_poweroff(void)
> +{
> +	schedule_delayed_work(&emergency_poweroff_work,
> +			      msecs_to_jiffies(CONFIG_THERMAL_EMERGENCY_POWEROFF_DELAY_MS));
> +}
> +
>  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;
> +	static struct mutex poweroff_lock;
>  
> +	mutex_init(&poweroff_lock);
>  	tz->ops->get_trip_temp(tz, trip, &trip_temp);
>  

the above is probably a quirk?

>  	/* If we have not crossed the trip_temp, we do not care. */
> @@ -345,6 +387,11 @@ static void handle_critical_trips(struct thermal_zone_device *tz,
>  			  "critical temperature reached(%d C),shutting down\n",
>  			  tz->temperature / 1000);
>  		mutex_lock(&poweroff_lock);
> +		/*
> +		 * Queue a backup emergency shutdown in the event of
> +		 * orderly_poweroff failure.
> +		 */
> +		thermal_emergency_poweroff();
>  		orderly_poweroff(true);
>  		power_off_triggered = true;
>  		mutex_unlock(&poweroff_lock);
> -- 
> 1.9.1
> 

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