Re: [PATCH v4 2/2] thermal: core: Add a back up thermal shutdown mechanism

[Eduardo Valentin]

Hey,

On Fri, Apr 14, 2017 at 02:22:13PM +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.
> 
> Reported-by: Nishanth Menon <nm@xxxxxx>
> Signed-off-by: Keerthy <j-keerthy@xxxxxx>
> ---
> 
> Changes in v4:
> 
>   * Updated documentation
>   * changed emergency_poweroff_func to thermal_emergency_poweroff_func
> 
> Changes in v3:
> 
>   * Removed unnecessary mutex init.
>   * Added WARN messages instead of a simple warning message.
>   * Added Documentation.
> 
>  Documentation/thermal/sysfs-api.txt | 19 +++++++++++++++
>  drivers/thermal/Kconfig             | 13 +++++++++++
>  drivers/thermal/thermal_core.c      | 46 +++++++++++++++++++++++++++++++++++++
>  3 files changed, 78 insertions(+)
> 
> diff --git a/Documentation/thermal/sysfs-api.txt b/Documentation/thermal/sysfs-api.txt
> index ef473dc..e73cc12 100644
> --- a/Documentation/thermal/sysfs-api.txt
> +++ b/Documentation/thermal/sysfs-api.txt
> @@ -582,3 +582,22 @@ platform data is provided, this uses the step_wise throttling policy.
>  This function serves as an arbitrator to set the state of a cooling
>  device. It sets the cooling device to the deepest cooling state if
>  possible.
> +
> +6. thermal_emergency_poweroff:
> +
> +On an event of critical trip temperature crossing. Thermal framework
> +allows the system to shutdown gracefully by calling orderly_poweroff().
> +In the event of a failure of orderly_poweroff() to shut down the system
> +we are in danger of keeping the system alive at undesirably high
> +temperatures. To mitigate this high risk scenario we program a work
> +queue to fire after a pre-determined number of seconds to start
> +an emergency shutdown of the device using the kernel_power_off()
> +function. In case kernel_power_off() fails then finally
> +emergency_restart() is called in the worst case.
> +
> +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 emergency poweroff will happen immediately.
> diff --git a/drivers/thermal/Kconfig b/drivers/thermal/Kconfig
> index 9347401..0dd5b85 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

Only now I realized that merging this may break the working
orderly_poweroff() out there, because you are defaulting this to 0, no
delay, therefore giving no time for orderly_poweroff() to finish. This
is not good.

I think using 0 delay as immediate power off is not good as we give no
time for graceful shutdown, and by default. My suggestion here
is to use 0 delay as no forced shutdown. Meaning, by default, this
feature is disabled, and all other systems out there, despite DRA7 with
arago over NFS, work as before.

> +	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 8337c27..aed614d 100644
> --- a/drivers/thermal/thermal_core.c
> +++ b/drivers/thermal/thermal_core.c
> @@ -324,6 +324,47 @@ static void handle_non_critical_trips(struct thermal_zone_device *tz,
>  		       def_governor->throttle(tz, trip);
>  }
>  
> +/**
> + * thermal_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 thermal_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
> +	 */
> +	WARN(1, "Attempting kernel_power_off: Temperature too high\n");
> +	kernel_power_off();
> +
> +	/*
> +	 * Worst of the worst case trigger emergency restart
> +	 */
> +	WARN(1, "Attempting emergency_restart: Temperature too high\n");
> +	emergency_restart();
> +}
> +
> +static DECLARE_DELAYED_WORK(thermal_emergency_poweroff_work,
> +			    thermal_emergency_poweroff_func);
> +
> +/**
> + * thermal_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(&thermal_emergency_poweroff_work,
> +			      msecs_to_jiffies(CONFIG_THERMAL_EMERGENCY_POWEROFF_DELAY_MS));

So, please, only schedule if delay is greater than 0. 

Also I would prefer the config is set to a local variable..
> +}
> +
>  static void handle_critical_trips(struct thermal_zone_device *tz,
>  				  int trip, enum thermal_trip_type trip_type)
>  {
> @@ -346,6 +387,11 @@ static void handle_critical_trips(struct thermal_zone_device *tz,
>  			  tz->temperature / 1000);
>  		mutex_lock(&poweroff_lock);
>  		if (!power_off_triggered) {
> +			/*
> +			 * Queue a backup emergency shutdown in the event of
> +			 * orderly_poweroff failure
> +			 */
> +			thermal_emergency_poweroff();
>  			orderly_poweroff(true);
>  			power_off_triggered = true;
>  		}
> -- 
> 1.9.1
>

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