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

[Keerthy <j-keerthy@ti.com>]

On Friday 14 April 2017 11:48 PM, Eduardo Valentin wrote:
> Hey,
> 
> On Fri, Apr 14, 2017 at 08:42:20AM -0700, Eduardo Valentin wrote:
>> Hello again,
>>
>> On Fri, Apr 14, 2017 at 08:38:40AM -0700, Eduardo Valentin wrote:
>>> 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@ti.com>
>>>> Signed-off-by: Keerthy <j-keerthy@ti.com>
>>>> ---
>>>>
>>>> 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.
> 
> A better solution could be to have bool Kconfig, say
> THERMAL_EMERGENCY_POWEROFF, which would default to false. If one selects
> that option, you get the DELAY_MS configurable, and then you could get
> the 0 ms still as a valid entry, with the same semantics of immediate
> power off, no orderly_poweroff.
> 
> I just want to avoid breaking everybody (or changing userland
> expectation) in honor of this change.

Sure. I have now used default value as no emergency shutdown.
Any positive value is taken as the delay value.

Sent a v5.

> 
>>>
>>>> +	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. 
>>
>> Please update documentation accordingly..
>>
> 
>