Re: [PATCH v3 5/6] fs/resctrl: Do not invoke smp_processor_id() in preemptible context

[Luck, Tony]

On Mon, Jun 08, 2026 at 07:26:30PM +0800, Chen, Yu C wrote:
> On 6/8/2026 4:36 PM, Thomas Gleixner wrote:
> > On Sat, Jun 06 2026 at 10:38, Chen Yu wrote:
> > > From: Tony Luck <tony.luck@xxxxxxxxx>
> > > 
> > > __l3_mon_event_count() and __l3_mon_event_count_sum() call
> > > smp_processor_id() to obtain the current CPU. However, some
> > > monitor events can be read from any CPU in task context via
> > > mon_event_count(); in that case the calling context is
> > > preemptible and smp_processor_id() triggers a debug warning.
> > 
> > Is this new with this MMIO stuff or is this an existing issue? If the
> > latter then this patch should be in front of the series and get a fixes
> > tag. If not the change log should explain it.
> > 
> 
> It is an existing issue. I'll adjust the sequence and provide a fixes tag.
> Thanks!

I don't think this is an existing issue. Before addition of MMIO
registers access is via the IA32_QM_EVTSEL and IA32_QM_CTR MSRs
which require access from a CPU on the same domain.

-Tony