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

[Rafael J. Wysocki (Intel)]

On Thu, Jul 23, 2026 at 4:46 PM Bradley Morgan <include@xxxxxxxxx> wrote:
>
> On July 23, 2026 2:55:41 PM GMT+01:00, "Rafael J. Wysocki (Intel)"
> <rafael@xxxxxxxxxx> wrote:
> >On Tue, Jul 21, 2026 at 5:14 PM Bradley Morgan <include@xxxxxxxxx> 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/20260719231540.455bd5c3eac842686c05bd7f@xxxxxxxxxxxxxxxxxxxx/
>
> [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.