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

[Chen, Yu C]

Hi Tony,

On 6/8/2026 11:32 PM, Luck, Tony wrote:
> 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.

Thanks for pointing this out. Right, [PATCH 5/6] serves as a preparatory
patch to enable MMIO reads  for RDT_RESOURCE_L3 within a preemptible 
context.
I had overlooked that any_cpu was set to false for RDT_RESOURCE_L3. any_cpu
will only be enabled  for QOS_L3_OCCUP_EVENT_ID in [PATCH 6/6].

thanks,
Chenyu