linux-kernel - Re: [PATCH 4.19 65/71] powerpc/pseries: Do not initiate shutdown when system is running on UPS

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Date:   Wed, 26 Aug 2020 16:44:12 +0530
From:   Vasant Hegde <hegdevasant@...ux.vnet.ibm.com>
To:     Pavel Machek <pavel@...x.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Michael Ellerman <mpe@...erman.id.au>
Subject: Re: [PATCH 4.19 65/71] powerpc/pseries: Do not initiate shutdown when
 system is running on UPS

On 8/26/20 1:26 AM, Pavel Machek wrote:
> Hi!
> 

Hi Pavel,

>> We have a user space tool (rtas_errd) on LPAR to monitor for
>> EPOW_SHUTDOWN_ON_UPS. Once it gets an event it initiates shutdown
>> after predefined time. It also starts monitoring for any new EPOW
> 
> Yeah, so there's userspace tool, and currently systems _with_ that
> tool work poorly with UPS.
> 
> So you have fixed that, and now, systems _without_ that tool will work
> poorly.

User space tool exists for long long time (more than decade) and its default tool
on pseries system. Also user space tool behavior is not changed for long time.

The original design was to forward UPS event to userspace and let user space wait
for predefined time and then initiate shutdown.

Previous fix accidentally initiated shutdown as soon as system switch to UPS power.

> 
> That's not a fix for serious bug, that's behaviour change. You are
> fixing one set of systems and breaking another.

Without fix, as soon as system switches to UPS power supply, kernel will start 
shutdown process. which is not correct. Its actually impacting customers running 
Linux on pseries LPAR mode. Hence I have requested this fix for stable tree.

Hope this clarifies your concern.

-Vasant

> 
> I don't believe it is suitable for stable.
> 
> 								Pavel
> 
>> @@ -118,7 +118,6 @@ static void handle_system_shutdown(char
>>   	case EPOW_SHUTDOWN_ON_UPS:
>>   		pr_emerg("Loss of system power detected. System is running on"
>>   			 " UPS/battery. Check RTAS error log for details\n");
>> -		orderly_poweroff(true);
>>   		break;
>>   
>>   	case EPOW_SHUTDOWN_LOSS_OF_CRITICAL_FUNCTIONS:
>>
>