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

[Adrian Hunter <adrian.hunter@intel.com>]

On 02/11/2026 11:06, Peter Zijlstra wrote:
> On Mon, Nov 02, 2026 at 09:40:34AM +0200, Adrian Hunter wrote:
>> irq_work_queue() raises the irq_work self-interrupt only when adding
>> work to an empty raised_list.  Once raised_list is non-empty, further
>> queueing assumes the interrupt is already pending and will eventually
>> process the list.
>>
>> That assumption can fail across system suspend.  irq_work queued after
>> arch_suspend_disable_irqs() and before the interrupt controller is
>> suspended, for example from NMI context, may leave its self-interrupt
>> pending in hardware.  If that pending interrupt state is lost during
>> suspend, hibernation restore, or kexec jump, raised_list remains
>> non-empty after resume but nothing will process it.
>>
>> Subsequent irq_work added to raised_list will not raise another
>> interrupt because the list is already non-empty.  Architectures that use
>> an irq_work interrupt and do not process raised_list from the tick can
>> therefore leave irq_work pending indefinitely.  A caller waiting in
>> irq_work_sync() may then spin forever, for example when closing a perf
>> event whose pending irq_work never executes.
>>
>> For suspend, hibernation, and kexec jump, only the CPU that remains
>> online is affected.  The other CPUs are taken offline beforehand, and
>> smpcfd_dying_cpu() runs irq_work_run() on each CPU before it is removed,
>> so checking the local raised_list is sufficient.
> 
> I thought here was a suspend2idle option where all the CPUs remain
> online?

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.

> suspend pause/resume perf in a more controlled manner.

For fixing Intel PT though, it also needs to be suitable for stable.