On Mon 23-09-19 22:34:10, Peter Zijlstra wrote:

On Mon, Sep 23, 2019 at 06:52:35PM +0200, Michal Hocko wrote:

[...]

quoted

I even the
ACPI standard is considering this optional. Yunsheng Lin has referred to
the specific part of the standard in one of the earlier discussions.
Trying to guess the node affinity is worse than providing all CPUs IMHO.

I'm saying the ACPI standard is wrong.

Even if you were right on this the reality is that a HW is likely to
follow that standard and we cannot rule out NUMA_NO_NODE being
specified. As of now we would access beyond the defined array and that
is clearly a bug.

Let's assume that this is really a bug for a moment. What are you going
to do about that? BUG_ON? I do not really see any solution besides to either
provide something sensible or BUG_ON. If you are worried about a
conditional then this should be pretty easy to solve by starting the
array at -1 index and associate it with the online cpu mask.
-- 
Michal Hocko
SUSE Labs