Re: [PATCH 1/6] irq_work: Re-raise pending irq_work after system resume

[Adrian Hunter]

On 04/11/2026 09:32, Sebastian Andrzej Siewior wrote:
> On 2026-11-03 17:46:32 [+0200], Adrian Hunter wrote:
>> On 02/11/2026 18:39, Sebastian Andrzej Siewior wrote:
>>> On 2026-11-02 12:54:22 [+0200], Adrian Hunter wrote:
>>>>
>>>> Yes CPUs remain online for suspend2idle, but currently the choice between
>>>> suspend2idle and "deep" (S3) suspend is a user space choice,
>>>> refer /sys/power/mem_sleep.  Many modern systems do not support S3
>>>> anymore, but it has not gone away.
>>>>
>>>>>
>>>>> Anyway, I'm torn; I would much rather make this trigger a WARN and have
>>>>
>>>> AI now also identifies ftrace, BPF, GHES NMI, and #MC as possible causes,
>>>> not just perf.  I haven't tried to confirm any of those.
>>>>
>>>> And, belatedly, AI is now saying an irq_work raised before lapic_resume()
>>>> might result in #GP if the APIC is left in xAPIC mode at resume.  Also
>>>> not confirmed.
>>>
>>> Could we flush this before similarly to what happens during CPU-hotplug.
>>> The question is if this event can stay enqueued during suspend (and
>>> handled on resume) or should be taken care before entering suspend.
>>
>> WRT "might result in #GP if the APIC is left in xAPIC mode at resume",
>> the systems I have checked restore the APIC in x2APIC mode, so the
>> issue is theoretical at this point, although I can get "unchecked MSR
>> access error: WRMSR to 0x83f" if I deliberately add code to change
>> x2APIC to xAPIC early in S3 wake (in x86_acpi_suspend_lowlevel()),
>> and then do:
>>
>>   perf record -e power:suspend_resume --filter 'action == "machine_suspend" && start == 0' --no-buffering -C 0 -o /tmp/x.data &
>>   rtcwake -m mem -s 10
>>
>> The error can be avoided with:
> 
> I meant flush it via irq_work_run_cpu() like in smpcfd_dead_cpu() (the
> CPU-hotplug path) and not go via APIC. You should do it late once the
> interrupts are disabled so no new irq-work can be enqueued.
Disabling IRQs doesn't stop NMI or syscore enqueues, and the resume-side
raise still goes through the APIC