[PATCH v1] kernel/reboot: Change registration order of legacy power-off handler

[Michael Ellerman]

Dmitry Osipenko <dmitry.osipenko at collabora.com> writes:
> Hi Michael,
>
> On 6/5/22 05:01, Michael Ellerman wrote:
>> Dmitry Osipenko <dmitry.osipenko at collabora.com> writes:
>>> We're unconditionally registering sys-off handler for the legacy
>>> pm_power_off() callback, this causes problem for platforms that don't
>>> use power-off handlers at all and should be halted. Now reboot syscall
>>> assumes that there is a power-off handler installed and tries to power
>>> off system instead of halting it.
>>>
>>> To fix the trouble, move the handler's registration to the reboot syscall
>>> and check the pm_power_off() presence.
>>
>> I'm seeing a qemu virtual machine (ppce500) fail to power off using the
>> gpio-poweroff driver. I bisected it to this commit.
>>
>> I think the problem is that the machine is going via kernel_power_off(),
>> not sys_reboot(), and so legacy_pm_power_off() has not been registered.
>>
>> If I just put the core_initcall back then it works as before. Not sure
>> if that's a safe change in general though.
>
> Thank you very much for the testing and reporting the problem! I see now the two more cases that were missed previously:
>
> 1. There is the orderly_poweroff() used by some drivers.
> 2. PowerPC may invoke do_kernel_power_off() directly from xmon code.
>
> Could you please test this change:

That works, thanks.

I tested both sysrq-o and the xmon power off path.

I couldn't come up with an easy way to test the orderly_poweroff()
path, but it boils down to basically the same code in the end.

Tested-by: Michael Ellerman <mpe at ellerman.id.au>

cheers