Subject: Re: [PATCH v3 3/5] powerpc/numa: Use cpu node map of first sibling thread

From: Nathan Lynch <[email-masked]>
Date: Thu, 12 Sep 2019 13:15:03 -0500

Srikar Dronamraju <[email-masked]> writes:

>> 
>> I think just WARN_ON(cpu_online(fcpu)) would be satisfactory. In my
>> experience, the downstream effects of violating this condition are
>> varied and quite difficult to debug. Seems only appropriate to emit a
>> warning and stack trace before the OS inevitably becomes unstable.
>
> I still have to try but wouldn't this be a problem for the boot-cpu?
> I mean boot-cpu would be marked online while it tries to do numa_setup_cpu.
> No?

This is what I mean:

 +      if (fcpu != lcpu) {
 +              WARN_ON(cpu_online(fcpu));
 +              map_cpu_to_node(fcpu, nid);
 +      }

I.e. if we're modifying the mapping for a remote cpu, warn if it's
online.

I don't think this would warn on the boot cpu -- I would expect fcpu and
lcpu to be the same and this branch would not be taken.