Date:   Wed, 12 Apr 2017 21:43:00 +0300
From:   Tero Kristo <t-kristo@...com>
To:     Eduardo Valentin <edubezval@...il.com>, Keerthy <j-keerthy@...com>
CC:     Grygorii Strashko <grygorii.strashko@...com>,
        Zhang Rui <rui.zhang@...el.com>, <linux-pm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-omap@...r.kernel.org>,
        <nm@...com>
Subject: Re: [PATCH] thermal: core: Add a back up thermal shutdown mechanism

On 12/04/17 20:24, Eduardo Valentin wrote:
> On Wed, Apr 12, 2017 at 10:41:00PM +0530, Keerthy wrote:
>>
>>
>> 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?
>
> It is still useful on a properly sized system. The point is the thermal
> subsystem still wants to give one opportunity to gracefully shutdown the
> running system on a thermal scenario, as I explained in the other email.
> But, you have to do this accounting the down time, and your reliability
> concerns.
>
>>>
>>>
>>>>>>
>>>>>
>>>>>
>>>>> 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!
>>
>
> As I mentioned, the fix is a two fold, a. avoid spam of
> orderly_poweroff(), but make sure eventually we shutdown.

Just chirping in here a bit myself also, the long latencies in the 
poweroff executing are basically because in our case it will do all of 
the following:

- stop all running daemons
- kill all remaining processes
- unload all modules
- sync / unmount all filesystems
- etc.
- poweroff the system when everything else has been gracefully done

The order of these things are not necessarily what I listed above, but 
overall it takes quite a bit of time. It doesn't matter if you execute 
all of this over NFS or SD card or ramdisk, it is a long procedure.

-Tero

>
>>>
>>> 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.
>>>>>>
>>>>>>
>>>>>
>>>

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