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

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Date:   Wed, 12 Apr 2017 22:41:00 +0530
From:   Keerthy <j-keerthy@...com>
To:     Grygorii Strashko <grygorii.strashko@...com>,
        Eduardo Valentin <edubezval@...il.com>,
        Zhang Rui <rui.zhang@...el.com>
CC:     <linux-pm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-omap@...r.kernel.org>, <nm@...com>, <t-kristo@...com>
Subject: Re: [PATCH] thermal: core: Add a back up thermal shutdown mechanism



On Wednesday 12 April 2017 10:38 PM, Grygorii Strashko wrote:
> 
> 
> On 04/12/2017 11:44 AM, Keerthy wrote:
>>
>>
>> On Wednesday 12 April 2017 10:01 PM, Grygorii Strashko wrote:
>>>
>>>
>>> On 04/12/2017 10:44 AM, Eduardo Valentin wrote:
>>>> Hello,
>>>>
>>> ...
>>>
>>>>
>>>> I agree. But there it nothing that says it is not reenterable. If you
>>>> saw something in this line, can you please share?
>>>>
>>>>>>> will you generate a patch to do this?
>>>>>> Sure. I will generate a patch to take care of 1) To make sure that
>>>>>> orderly_poweroff is called only once right away. I have already
>>>>>> tested.
>>>>>>
>>>>>> for 2) Cancel all the scheduled work queues to monitor the
>>>>>> temperature.
>>>>>> I will take some more time to make it and test.
>>>>>>
>>>>>> Is that okay? Or you want me to send both together?
>>>>>>
>>>>> I think you can send patch for step 1 first.
>>>>
>>>> I am happy to see that Keerthy found the problem with his setup and a
>>>> possible solution. But I have a few concerns here.
>>>>
>>>> 1. If regular shutdown process takes 10seconds, that is a ballpark that
>>>> thermal should never wait. orderly_poweroff() calls run_cmd() with wait
>>>> flag set. That means, if regular userland shutdown takes 10s, we are
>>>> waiting for it. Obviously this not acceptable. Specially if you setup
>>>> critical trip to be 125C. Now, if you properly size the critical trip to
>>>> fire before hotspot really reach 125C, for 10s (or the time it takes to
>>>> shutdown), then fine. But based on what was described in this thread,
>>>> his system is waiting 10s on regular shutdown, and his silicon is on
>>>> out-of-spec temperature for 10s, which is wrong.
>>>>
>>>> 2. The above scenario is not acceptable in a long run, specially from a
>>>> reliability perspective. If orderly_poweroff() has a possibility to
>>>> simply never return (or take too long), I would say the thermal
>>>> subsystem is using the wrong API.
> 
> ^ this question just repeat everything which was already discussed in
> previous versions of this patch - orderly_poweroff() is not good for critical shutdown/poweroff,
> but what to use instead?
> 
> 
>>>>
>>>
>>>
>>> Hh, I do not see that orderly_poweroff() will wait for anything now:
>>> void orderly_poweroff(bool force)
>>> {
>>> 	if (force) /* do not override the pending "true" */
>>> 		poweroff_force = true;
>>> 	schedule_work(&poweroff_work); 
>>> ^^^^^^^ async call. even here can be pretty big delay if system is under pressure
>>> }
>>>
>>>
>>> static int __orderly_poweroff(bool force)
>>> {
>>> 	int ret;
>>>
>>> 	ret = run_cmd(poweroff_cmd);
>>
>> When i tried with multiple orderly_poweroff calls ret was always 0.
>> So every 250mS i see this ret = 0.
>>
>>> ^^^^ no wait for the process - only for exec. flags == UMH_WAIT_EXEC
>>>
>>> 	if (ret && force) {
>>
>> So it never entered this path. ret = 0 so if is not executed.
> 
> correct, because exec can find poweroff tool and start it, so you,
> most probably, have bunch of this tool instance running in parallel (some of them can fail or block)
> Issue 1 - you've sent fix for is actual :).

Precisely yes!

> 
> Again, thermal has no control of power off process once  run_cmd() is returned,
> and it do not know what US poweroff binary is doing and how much time can it take
> (which include disks maintenance - loooong delay).
> 
>>
>>> 		pr_warn("Failed to start orderly shutdown: forcing the issue\n");
>>>
>>> 		/*
>>> 		 * I guess this should try to kick off some daemon to sync and
>>> 		 * poweroff asap.  Or not even bother syncing if we're doing an
>>> 		 * emergency shutdown?
>>> 		 */
>>> 		emergency_sync();
>>> 		kernel_power_off();
>>> ^^^ force power off, but only if run_cmd() failed - for example /sbin/poweroff doesn't exist
>>> 	}
>>>
>>> 	return ret;
>>> }
>>>
>>> static bool poweroff_force;
>>>
>>> static void poweroff_work_func(struct work_struct *work)
>>> {
>>> 	__orderly_poweroff(poweroff_force);
>>> }
>>>
>>> As result thermal has no control of power off any more after calling orderly_poweroff() and can get the result
>>> of US poweroff binary execution.
>>>
>>>>
>>>> If you are going to implement the above two patches, keep in mind:
>>>> i. At least within the thermal subsystem, you need to take care of all
>>>> zones that could trigger a shutdown.
>>>> ii. serializing the calls to orderly_poweroff() seams to be more
>>>> concerning than cancelling all monitoring.
>>>>
>>>>
>>>
>