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

[Eduardo Valentin <edubezval@gmail.com>]

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Hey,

On Fri, Mar 31, 2017 at 12:00:20PM +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).

OK... This seams to me, still a corner case supposed to be fixed at
orderly_power_off, not at thermal. But..

> 
> 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.
> 

Given that system running hot is a thermal issue, I guess we care more
on this matter then..

> Reported-by: Nishanth Menon <nm@ti.com>
> Signed-off-by: Keerthy <j-keerthy@ti.com>
> ---
>  drivers/thermal/Kconfig        | 13 +++++++++++++
>  drivers/thermal/thermal_core.c | 42 ++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 55 insertions(+)
> 
> diff --git a/drivers/thermal/Kconfig b/drivers/thermal/Kconfig
> index 0a16cf4..4cc55f9 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 11f0675..dc7fdd4 100644
> --- a/drivers/thermal/thermal_core.c
> +++ b/drivers/thermal/thermal_core.c
> @@ -322,6 +322,47 @@ 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 pm_power_off
> +	 * if populated
> +	 */

The above is not a kernel doc entry...

> +	pr_warn("Attempting kernel_power_off\n");
> +	if (pm_power_off)
> +		pm_power_off();

Why not calling kernel_power_off() directly instead? That is what is called by orderly
power off in case it fails, which seams to be  the missing part when
user land returns success, and therefore we don't call
kernel_power_off(). That path goes through the machine_power_off(),
which seams to be the default for pm_power_off() anyway.

kernel_power_off() handles the power off system call too.

> +
> +	/**

not a kernel doc entry...

> +	 * Worst of the worst case trigger emergency restart
> +	 */
> +	pr_warn("kernel_power_off has failed! Attempting emergency_restart\n");
> +	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)
>  {
> @@ -343,6 +384,7 @@ static void handle_critical_trips(struct thermal_zone_device *tz,
>  			  "critical temperature reached(%d C),shutting down\n",
>  			  tz->temperature / 1000);
>  		orderly_poweroff(true);
> +		thermal_emergency_poweroff();

Shouldn't we start count the timeout before calling orderly_poweroff?

>  	}
>  }
>  
> -- 
> 1.9.1
> 

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