Re: [PATCH v8 07/27] kernel/reboot: Add kernel_can_power_off()

[Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx>]

On 5/24/22 18:03, Geert Uytterhoeven wrote:
> Hi Dmitry,
> 
> On Tue, May 24, 2022 at 3:41 PM Dmitry Osipenko
> <dmitry.osipenko@xxxxxxxxxxxxx> wrote:
>> On 5/24/22 16:14, Geert Uytterhoeven wrote:
>>> On Tue, May 10, 2022 at 1:33 AM Dmitry Osipenko
>>> <dmitry.osipenko@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx>
>>>
>>> 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@xxxxxxxxx>

Great! I'll send the proper patch soon.

-- 
Best regards,
Dmitry