Date:   Tue, 2 May 2017 09:10:53 +0530
From:   Keerthy <j-keerthy@...com>
To:     <rui.zhang@...el.com>
CC:     Ravikumar <rk@...com>, <edubezval@...il.com>,
        <linux-pm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-omap@...r.kernel.org>, <nm@...com>, <t-kristo@...com>
Subject: Re: [PATCH v6 2/2] thermal: core: Add a back up thermal shutdown
 mechanism



On Tuesday 18 April 2017 11:48 AM, Keerthy wrote:
> 
> 
> On Tuesday 18 April 2017 11:45 AM, Ravikumar wrote:
>>
>>
>> On Tuesday 18 April 2017 09:59 AM, 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.
>> Care to add testing information?
> 
> I used THERMAL_EMULATION to fake temperature more than trip point.
> If the delay is lesser (< 20S) then i see that backup poweroff is called
> and the system shuts down immediately after the delay time expires else
> orderly_poweroff gracefully shuts off the system. I do not have the logs
> right now.
> 
>>> Reported-by: Nishanth Menon <nm@...com>
>>> Signed-off-by: Keerthy <j-keerthy@...com>
>>> Acked-by: Eduardo Valentin <edubezval@...il.com>

Zhang,

Could you pull this one also?

- Keerthy
>>> ---
>>>
>>> Changes in v6:
>>>
>>>    * Rephrased Kconfig description as per Eduardo's feedback.
>>>    * Added check to verify positive values of delay in milli Seconds.
>>>
>>> Changes in v5:
>>>
>>>    * Mandated delay for thermal emergency poweroff to be a non-zero
>>> value.
>>>
>>> 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 | 21 +++++++++++++++
>>>   drivers/thermal/Kconfig             | 17 ++++++++++++
>>>   drivers/thermal/thermal_core.c      | 53
>>> +++++++++++++++++++++++++++++++++++++
>>>   3 files changed, 91 insertions(+)
>>>
>>> diff --git a/Documentation/thermal/sysfs-api.txt
>>> b/Documentation/thermal/sysfs-api.txt
>>> index ef473dc..bb9a0a5 100644
>>> --- a/Documentation/thermal/sysfs-api.txt
>>> +++ b/Documentation/thermal/sysfs-api.txt
>>> @@ -582,3 +582,24 @@ 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:
>>> +
>> Should this be in sysfs-api doc?
>>> +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.
>>> +
>> In order to come up with an ideal delay, we need to strike a balance
>> between
>> being paranoid vs being too late.
>> In a different patch, I tried to justify setting crit temp @120C by quoting
>> we need to give some time to orderly_poweroff()
>>
>> So we got T = [3/temp change rate] seconds before the HW issues a reset.
>>
>> within this T sec we need to give a chance to orderly_poweroff() and
>> when it
>> fails, bring out the big weapons.
>>
>> crumb: we might actually be increasing the "temp rate change" by doing a
>> lot of IO
>> access for syncing.
>> Let us hope someone is trying to cool the system down while we are
>> trying to
>> save the day..
>>> +If set to 0 emergency poweroff will not be supported. So a carefully
>>> +profiled non-zero positive value is a must for emergerncy poweroff to be
>>> +triggered.
>> Profiling should be done based on real data than emulation.
>> That's when we get to know if the memory and IOs listen to the SoC
>> when the lava is out.
>>> diff --git a/drivers/thermal/Kconfig b/drivers/thermal/Kconfig
>>> index 9347401..74bf92b 100644
>>> --- a/drivers/thermal/Kconfig
>>> +++ b/drivers/thermal/Kconfig
>>> @@ -15,6 +15,23 @@ menuconfig THERMAL
>>>     if THERMAL
>>>   +config THERMAL_EMERGENCY_POWEROFF_DELAY_MS
>>> +    int "Emergency poweroff delay in milli-seconds"
>>> +    depends on THERMAL
>>> +    default 0
>>> +    help
>>> +      Thermal subsystem will issue a graceful shutdown when
>>> +      critical temperatures are reached using orderly_poweroff(). In
>>> +      case of failure of an orderly_poweroff(), the thermal emergency
>>> +      poweroff kicks in after a delay has elapsed and shuts down the
>>> system.
>>> +      This config is number of milliseconds to delay before emergency
>>> +      poweroff kicks in. Similarly to the critical trip point,
>>> +      the delay should be carefully profiled so as to give adequate
>>> +      time for orderly_poweroff() to finish on regular execution.
>>> +      If set to 0 emergency poweroff will not be supported.
>>> +
>>> +      In doubt, leave as 0.
>>> +
>>>   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..b21b9cc 100644
>>> --- a/drivers/thermal/thermal_core.c
>>> +++ b/drivers/thermal/thermal_core.c
>>> @@ -324,6 +324,54 @@ 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
>> may needs to be re-phrased as this func itself can't handle the 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
>> Here you may say after a pre-set delay.
>>> + *
>>> + * This may be called from any critical situation to trigger a system
>>> shutdown
>>> + * after a known period of time. By default this is not scheduled.
>> This will be called only on a critical temperature event, right?
>>> + */
>>> +void thermal_emergency_poweroff(void)
>>> +{
>>> +    int poweroff_delay_ms = CONFIG_THERMAL_EMERGENCY_POWEROFF_DELAY_MS;
>>> +    /*
>>> +     * poweroff_delay_ms must be a carefully profiled positive value.
>>> +     * Its a must for thermal_emergency_poweroff_work to be scheduled
>> typo %s/Its/It's/
>>> +     */
>>> +    if (poweroff_delay_ms <= 0)
>>> +        return;
>> It may be helpful to provide hint before returning?
>> "Back up thermal emergency poweroff service is not enabled, set
>>
>> CONFIG_THERMAL_EMERGENCY_POWEROFF_DELAY_MS to a carefully profiled value
>> to enable this service"
>>
>>> +    schedule_delayed_work(&thermal_emergency_poweroff_work,
>>> +                  msecs_to_jiffies(poweroff_delay_ms));
>>> +}
>>> +
>>>   static void handle_critical_trips(struct thermal_zone_device *tz,
>>>                     int trip, enum thermal_trip_type trip_type)
>>>   {
>>> @@ -346,6 +394,11 @@ 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();
>> This comment is misleading because calling the api is not enough to set
>> a backup.
>>>               orderly_poweroff(true);
>>>               power_off_triggered = true;
>>>           }
>> Over all, much needed functionality. Thanks.
>>
>> Regards,
>> RK

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