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

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Message-ID: <4300a3d4-76de-70c5-2a7b-c4d066ef5bc6@gmail.com>
Date:   Tue, 19 Oct 2021 12:03:58 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     "Rafael J. Wysocki" <rafael.j.wysocki@...el.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 10/19/21 11:53 AM, Rafael J. Wysocki wrote:
> 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.

Reverting my commit will break powerpc and other ARM/ARM64 platforms
where mem is not supported (via PSCI), I have a change pending for PSCI
that will actually check that SYSTEM_SUSPEND is supported before
unconditionally making use of it.

> 
> 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.

So how do we all get our cookie here? Should we just slap an #ifndef
CONFIG_ACPI in order to allow platforms that do not have "mem" to not
have it?
-- 
Florian