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Wysocki" Cc: "Rafael J. Wysocki" , LKML , Linux Memory Management List , lkp@lists.01.org, kbuild test robot , kernel test robot , Linux PM References: <20211014075731.GB18719@xsang-OptiPlex-9020> <51c0a15f-1941-f161-dcec-a7a9acc726f2@gmail.com> <6755cf07-fa5a-cbb7-c076-57c162a08c99@gmail.com> <20aedfba-14e3-3677-d21a-b87610095445@gmail.com> <4300a3d4-76de-70c5-2a7b-c4d066ef5bc6@gmail.com> <8ebd1cad-fa35-8ad8-0be5-3dd3364196cb@gmail.com> From: Florian Fainelli Message-ID: <0941a29e-e035-aaca-ecc4-6505f8fe1ad1@gmail.com> Date: Wed, 20 Oct 2021 11:17:17 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/20/21 9:00 AM, Rafael J. Wysocki wrote: > On Wed, Oct 20, 2021 at 5:34 PM Florian Fainelli wrote: >> >> >> >> On 10/20/2021 6:49 AM, Rafael J. Wysocki wrote: >>> On Tue, Oct 19, 2021 at 9:04 PM Florian Fainelli wrote: >>>> >>>> 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 >>>>>>>>>> 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), >>> >>> It won't break anything, although the things that didn't work before >>> will still not work after it. >>> >>> And "mem" is always supported even if there are no suspend_ops at all, >>> in which case it becomes an alternative way to trigger s2idle. >>> >>> So, on the affected systems, what's there in /sys/power/? Is >>> mem_sleep present? If so, what's in it? >> >> With 4.9 which is what I used initially: >> >> # cat /sys/power/state >> freeze standby >> # cat /sys/power/ >> pm_async pm_print_times pm_wakeup_irq wakeup_count >> pm_freeze_timeout pm_test state >> >> With a newer kernel without my patch: >> >> # cat /sys/power/state >> freeze standby mem >> # cat /sys/power/mem_sleep >> s2idle shallow [deep] > > OK, so the "deep" and "shallow" suspend variants appear to be > supported. What's the problem with advertising "mem" then? s2idle and shallow are, but deep is not. > >> # cat /sys/power/ >> mem_sleep pm_freeze_timeout pm_wakeup_irq wakeup_count >> pm_async pm_print_times state >> pm_debug_messages pm_test suspend_stats/ >> >> >>> >>>> 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? >>> >>> Certainly not. >>> >>> I've just hacked my test-bed system with ACPI so it does not register >>> any suspend_ops at all and I have "freeze mem disk" in >>> /sys/power/state and "s2idle" in /sys/power/mem_sleep. Writing "mem" >>> to /sys/power/state causes s2idle to be carried out. >>> >>> Since this is the expected behavior, I'm not sure what the problem is. >> >> The problem is advertising "mem" in /sys/power/state when the state is >> not actually supported by the platform firmware here, whether that >> translates into the form of s2idle or not. It is not supported, and it >> should not be there IMHO. > > Well, it is there, because some user space expects it to be there on > systems supporting any kind of system-wide suspend, including s2idle. > Like it or not. But that was not the case before 406e79385f32 ("PM / sleep: System sleep state selection interface rework") and clearly nobody complained about that, did they? > > If it is not there, the utilities in question assume that system-wide > suspend is not supported at all. What utilities do depend on that? That selftest that does not even check that "mem" is actually present in /sys/power/state and just fails its test if it is not, yes it's not great, but that can be fixed. > >> I was late to the game in identifying that, >> but the 4.9 kernel makes sense to me. >> >> Similarly, if you take arch/powerpc/sysdev/fsl_pmc.c only >> PM_SUSPEND_STANDBY is valid, so advertising mem would be wrong if we >> don't look at what ->valid tells us. > > Again: "mem" appears in /sys/power/state if the system supports any > kind of system-wide suspend (because of the expectations of user space > mentioned above) and mem_sleep decides what it really means. > > And this is documented too (see Documentation/admin-guide/pm/sleep-states.html). The documentation just states that if the kernel supports *any* suspend state, then /sys/power/state will be present and likewise for /sys/power/mem_sleep, it does not say what the contents will be and that "mem" would always be present in there. -- Florian