Re: [PATCH v13 11/32] x86,fs/resctrl: Handle events that can be read from any CPU

Luck, Tony
2025-10-30T15:54:18Z

On Thu, Oct 30, 2025 at 02:14:27PM +0800, Chen, Yu C wrote:
> Hi Tony,
>
> On 10/30/2025 12:20 AM, Tony Luck wrote:
> > resctrl assumes that monitor events can only be read from a CPU in the
> > cpumask_t set of each domain. This is true for x86 events accessed
> > with an MSR interface, but may not be true for other access methods such
> > as MMIO.
> >
> > Introduce and use flag mon_evt::any_cpu, settable by architecture, that
> > indicates there are no restrictions on which CPU can read that event.
> >
> > Signed-off-by: Tony Luck <tony.luck@intel.com>
>
> [snip]
>
> > -void resctrl_enable_mon_event(enum resctrl_event_id eventid)
> > +void resctrl_enable_mon_event(enum resctrl_event_id eventid, bool any_cpu)
> > {
> > if (WARN_ON_ONCE(eventid < QOS_FIRST_EVENT || eventid >= QOS_NUM_EVENTS))
> > return;
> > @@ -984,6 +984,7 @@ void resctrl_enable_mon_event(enum resctrl_event_id eventid)
> > return;
> > }
> > + mon_event_all[eventid].any_cpu = any_cpu;
> > mon_event_all[eventid].enabled = true;
> > }
>
> It seems that cpu_on_correct_domain() was dropped, due to
> the refactor of __mon_event_count() in patch 0006 means it is no
> longer needed. But we still invoke smp_processor_id() in preemptible
> context in __l3_mon_event_count() before further checkings, which would
> cause a warning.
> [ 4266.361951] BUG: using smp_processor_id() in preemptible [00000000] code:
> grep/1603
> [ 4266.363231] caller is __l3_mon_event_count+0x30/0x2a0
> [ 4266.364250] Call Trace:
> [ 4266.364262] <TASK>
> [ 4266.364273] dump_stack_lvl+0x53/0x70
> [ 4266.364289] check_preemption_disabled+0xca/0xe0
> [ 4266.364303] __l3_mon_event_count+0x30/0x2a0
> [ 4266.364320] mon_event_count+0x22/0x90
> [ 4266.364334] rdtgroup_mondata_show+0x108/0x390
> [ 4266.364353] seq_read_iter+0x10d/0x450
> [ 4266.364368] vfs_read+0x215/0x330
> [ 4266.364386] ksys_read+0x6b/0xe0
> [ 4266.364401] do_syscall_64+0x57/0xd70

I didn't notice this in my testing. Is this in your region aware
tree? If you are still using RDT_RESOURCE_L3 then I can see how
you got this call trace.

Maybe you need to dig cpu_on_correct_domain() back up and apply
it to __l3_mon_event_count()?

-Tony