>>>> Testing tip x86/cache that WARN fires while running
>>>> tools/tests/selftests/resctrl/resctrl_test.
>> 
>> I evidently need to build a newer version of that tool.
>
> There has been a lot of changes in the last few cycles. You can find the
> latest version on the "next" branch of the kselftest repo [1] where most recent
> enhancements are queued up for inclusion. If you are interested, there is one
> more series [2] pending merge to the kselftest repo, it adds a new test for
> the recent non-contiguous CBM support.

James,

You didn't see this WARN because it isn't in your patch. Diff between what
is in your tree and what was applied to TIP:

diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
index 9f1aa555a8ea..8a4ef4f5bddc 100644
--- a/arch/x86/kernel/cpu/resctrl/core.c
+++ b/arch/x86/kernel/cpu/resctrl/core.c
@@ -368,8 +368,8 @@ struct rdt_domain *get_domain_from_cpu(int cpu, struct rdt_resource *r)
         * about locks this thread holds will lead to false positives. Check
         * someone is holding the CPUs lock.
         */
-       if (IS_ENABLED(CONFIG_LOCKDEP))
-               lockdep_is_cpus_held();
+       if (IS_ENABLED(CONFIG_HOTPLUG_CPU) && IS_ENABLED(CONFIG_LOCKDEP))
+               WARN_ON_ONCE(!lockdep_is_cpus_held());

        list_for_each_entry(d, &r->domains, list) {
                /* Find the domain that contains this CPU */
diff --git a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
index dc59643498bf..7997b47743a2 100644
--- a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
+++ b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
@@ -567,7 +567,7 @@ void mon_event_read(struct rmid_read *rr, struct rdt_resource *r,
         * cpumask_any_housekeeping() prefers housekeeping CPUs, but
         * are all the CPUs nohz_full? If yes, pick a CPU to IPI.
         * MPAM's resctrl_arch_rmid_read() is unable to read the
-        * counters on some platforms if its called in irq context.
+        * counters on some platforms if its called in IRQ context.
         */
        if (tick_nohz_full_cpu(cpu))
                smp_call_function_any(&d->cpu_mask, mon_event_count, rr, 1);

-Tony