linux-kernel - Re: [PATCH v8 07/27] kernel/reboot: Add kernel_can_power

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Date:   Tue, 24 May 2022 17:03:19 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Dmitry Osipenko <dmitry.osipenko@...labora.com>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Russell King <linux@...linux.org.uk>,
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Subject: Re: [PATCH v8 07/27] kernel/reboot: Add kernel_can_power_off()

Hi Dmitry,

On Tue, May 24, 2022 at 3:41 PM Dmitry Osipenko
<dmitry.osipenko@...labora.com> wrote:
> On 5/24/22 16:14, Geert Uytterhoeven wrote:
> > On Tue, May 10, 2022 at 1:33 AM Dmitry Osipenko
> > <dmitry.osipenko@...labora.com> wrote:
> >> Add kernel_can_power_off() helper that replaces open-coded checks of
> >> the global pm_power_off variable. This is a necessary step towards
> >> supporting chained power-off handlers.
> >>
> >> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@...labora.com>
> >
> > Thanks for your patch, which is now commit 0e2110d2e910e44c
> > ("kernel/reboot: Add kernel_can_power_off()") in pm/linux-next.
> >
> > This causes the "poweroff" command (Debian nfsroot) to no longer
> > cleanly halt the system on arm32 systems, but fail with a panic
> > instead:
> >
> > -reboot: System halted
> > +reboot: Power down
> > +Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000000
> > +CPU: 0 PID: 1 Comm: systemd-shutdow Not tainted
> > 5.18.0-rc7-shmobile-00007-g0e2110d2e910 #1274
> > +Hardware name: Generic R-Car Gen2 (Flattened Device Tree)
> > + unwind_backtrace from show_stack+0x10/0x14
> > + show_stack from dump_stack_lvl+0x40/0x4c
> > + dump_stack_lvl from panic+0xf4/0x330
> > + panic from do_exit+0x1c8/0x8e4
> > + do_exit from __do_sys_reboot+0x174/0x1fc
> > + __do_sys_reboot from ret_fast_syscall+0x0/0x54
> > +Exception stack(0xf0815fa8 to 0xf0815ff0)
> > +5fa0:                   004e6954 00000000 fee1dead 28121969 4321fedc f0d94600
> > +5fc0: 004e6954 00000000 00000000 00000058 befa0c78 00000000 befa0c10 004e56f8
> > +5fe0: 00000058 befa0b6c b6ec8d45 b6e4a746
> > +---[ end Kernel panic - not syncing: Attempted to kill init!
> > exitcode=0x00000000 ]---
> >
> > On arm64, "poweroff" causes a clean "reboot: Power down" before/after.
> >
> > On both arm32 and arm64, the same handlers are registered:
> >   - SYS_OFF_MODE_POWER_OFF_PREPARE: legacy_pm_power_off_prepare
> >   - SYS_OFF_MODE_POWER_OFF: legacy_pm_power_off
> >
> > On both arm32 and arm64, legacy_pm_power_off_prepare() is called.
> > On both arm32 and arm64, legacy_pm_power_off() does not seem to
> > be called.
> >
> > On arm32, both pm_power_off_prepare and pm_power_off are NULL.
> > On arm64, pm_power_off_prepare is NULL, and
> > pm_power_off is psci_sys_poweroff.
> >
> > Do you have a clue?
> > Thanks!
>
> Thank you, Geert! I see the problem, the kernel_can_power_off() checks whether power-off handler is registered, but it's always registered because legacy_pm_power_off is registered unconditionally. So it causes trouble for platforms that don't have power-off handler installed at all. All platforms that I tested have a power-off handler, so now wonder that I didn't notice this before.
>
> This change should fix the problem, please give it a try:

Thank you, that fixes the problem for me!

Tested-by: Geert Uytterhoeven <geert+renesas@...der.be>

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds