linux-kernel - Re: [PM] bfcc1e67ff: kernel-selftests.breakpoints.step_after_suspend

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Date:   Tue, 19 Oct 2021 20:53:50 +0200
From:   "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
To:     Florian Fainelli <f.fainelli@...il.com>
CC:     LKML <linux-kernel@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        <lkp@...ts.01.org>, <lkp@...el.com>,
        kernel test robot <oliver.sang@...el.com>,
        Linux PM <linux-pm@...r.kernel.org>
Subject: Re: [PM] bfcc1e67ff:
 kernel-selftests.breakpoints.step_after_suspend_test.fail

On 10/15/2021 9:40 PM, Florian Fainelli wrote:
> On 10/15/21 11:45 AM, Rafael J. Wysocki wrote:
>> On 10/14/2021 11:55 PM, Florian Fainelli wrote:
>>> On 10/14/21 12:23 PM, Rafael J. Wysocki wrote:
>>>> On 10/14/2021 6:26 PM, Florian Fainelli wrote:
>>>>> On 10/14/21 12:57 AM, kernel test robot wrote:
>>>>>> Greeting,
>>>>>>
>>>>>> FYI, we noticed the following commit (built with gcc-9):
>>>>>>
>>>>>> commit: bfcc1e67ff1e4aa8bfe2ca57f99390fc284c799d ("PM: sleep: Do not
>>>>>> assume that "mem" is always present")
>>>>>> https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git
>>>>>> master
>>>>>>
>>>>>>
>>>>>> in testcase: kernel-selftests
>>>>>> version: kernel-selftests-x86_64-c8c9111a-1_20210929
>>>>>> with following parameters:
>>>>>>
>>>>>>       group: group-00
>>>>>>       ucode: 0x11
>>>>>>
>>>>>> test-description: The kernel contains a set of "self tests" under the
>>>>>> tools/testing/selftests/ directory. These are intended to be small
>>>>>> unit tests to exercise individual code paths in the kernel.
>>>>>> test-url: https://www.kernel.org/doc/Documentation/kselftest.txt
>>>>>>
>>>>>>
>>>>>> on test machine: 288 threads 2 sockets Intel(R) Xeon Phi(TM) CPU 7295
>>>>>> @ 1.50GHz with 80G memory
>>>>>>
>>>>>> caused below changes (please refer to attached dmesg/kmsg for entire
>>>>>> log/backtrace):
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> If you fix the issue, kindly add following tag
>>>>>> Reported-by: kernel test robot <oliver.sang@...el.com>
>>>>> Thanks for your report. Assuming that the code responsible for
>>>>> registering the suspend operations is drivers/acpi/sleep.c for your
>>>>> platform, and that acpi_sleep_suspend_setup() iterated over all
>>>>> possible
>>>>> sleep states, your platform must somehow be returning that
>>>>> ACPI_STATE_S3
>>>>> is not a supported state somehow?
>>>>>
>>>>> Rafael have you ever encountered something like that?
>>>> Yes, there are systems with ACPI that don't support S3.
>>> OK and do you know what happens when we enter suspend with "mem" in
>>> those cases? Do we immediately return because ultimately the firmware
>>> does not support ACPI S3?
>> "mem" should not be present in the list of available strings then, so it
>> should be rejected right away.
> Well yes, that was the purpose of the patch I submitted, but assuming
> that we did provide "mem" as one of the possible standby modes even
> though that was wrong (before patch), and the test was trying to enter
> ACPI S3 standby, what would have happened, would the ACPI firmware honor
> the request but return an error, or would it actually enter ACPI S3?
>
> In any case, I will change the test to check that this is a supported
> standby mode before trying it.

Unfortunately, I will need to revert bfcc1e67ff1e4aa8bfe2, because it 
breaks user space compatibility and that's got caught properly by the test.

What happens is that "mem" is a "pointer" to a secondary list of 
possible states and that generally is "s2idle shallow deep" and if 
s2idle is the only available option, it will be just "s2idle".

This list is there in /sys/power/mem_sleep.

It was done this way, because some variants of user space expect "mem" 
to be always present and don't recognize "freeze" properly.

Sorry for the confusion.