Re: [PATCH v2 3/3] PM: hibernate: log the task that initiated the power down

On July 23, 2026 3:55:10 PM GMT+01:00, "Rafael J. Wysocki (Intel)"
<[email protected]> wrote:
>On Thu, Jul 23, 2026 at 4:46 PM Bradley Morgan <[email protected]> wrote:
>>
>> On July 23, 2026 2:55:41 PM GMT+01:00, "Rafael J. Wysocki (Intel)"
>> <[email protected]> wrote:
>> >On Tue, Jul 21, 2026 at 5:14 PM Bradley Morgan <[email protected]>
>wrote:
>> >>
>> >> Give the hibernation power down the same treatment as the reboot
>> >> syscall commands.
>> >
>> >Why?
>>
>> 1: Andrew suggested it [1]
>> 2: because going down for hibernation is the same as "Wait, who the hell
>took the box down?!"
>
>No, it is not the same unless the system doesn't resume.
>
>> >
>> >> hibernate() runs in the context of the task that
>> >> asked for it, whether through the reboot syscall or a write to
>> >
>> >It doesn't use the reboot syscall.
>>
>> Hmmm.... I may embarrass myself here, but it *could* (wink)
>>
>> See kernel/reboot.c:
>>
>> #ifdef CONFIG_HIBERNATION
>>         case LINUX_REBOOT_CMD_SW_SUSPEND:
>>                 ret = hibernate();
>>                 break;
>> #endif
>
>Ah, I'm wondering if anyone actually uses this, but fair enough.
>
>> >> /sys/power/disk,
>>
>> I'm wrong: /sys/power/state
>>
>>  so when power_down() runs current is still the
>> >> initiating task.
>> >>
>> >> Log it once the image has been written and the machine is committed
>> >> to going down:
>> >>
>> >>   reboot: initiated by systemd-sleep[812]
>> >>   reboot: Power down
>> >>
>> >> The line comes from kernel/reboot.c so it keeps the "reboot:" prefix
>> >> and sits right next to the final "Restarting system", "Power down"
>> >> or "System halted" line, same as a plain reboot.
>> >>
>> >> The one exception is platform mode rolling back on a pending wakeup
>> >> event after the line has been printed. The existing "Wakeup event
>> >> detected during hibernation, rolling back." line follows immediately
>> >> in that case, so the log stays real about what happened.
>> >
>> >(a) Why is this information in the log useful?
>>
>> when the box just randomly goes down, some people prefer to know
>> "And what process did this? Or what did this?", say
>>
>> "Was it systemd-sleep? Or some random power daemon?? Or some stray
>> reboot(SW_SUSPEND)??"
>>
>> Userspace logging can't really do this...
>
>But it doesn't really go down in the case of hibernation.  It's more
>like suspend in that respect.
>
>> There is software out there which can do this, but it's not the
>greatest.
>> [2]
>>
>> Hence, this series!
>>
>> >(b) Do you realize that it only appears in the log when hibernation
>> >fails or it may appear on a serial console or similar?
>>
>> yeah. The image is written when the line prints, so after a successful
>> hibernate and resume dmesg won't have it.
>>
>> Thats exactly the
>> same visibility as the final "Power down" / "Restarting system"  line it
>> sits next to
>>
>> Well, if you want it, please say.
>>
>>
>> [1]:
>>
>https://lore.kernel.org/all/[email protected]/
>>
>> [2]: https://docs.memfault.com/docs/linux/reboot-reason-tracking
>>
>>
>> (oh and btw, if you don't buy in, it's ok, just say.. any questions,
>ask)
>> :)
>
>Yeah, I'm not convinced.
>


ack, dropped.

btw. I wasn't the surest anyway abt swusp, don't worry.

thanks for the review and sorry for wasting your time

Thanks!