Re: [PATCH 3/4] powerpc/numa: set node_possible_map from node_online_map

[Yury Norov <yury.norov@gmail.com>]

On Thu, Jul 02, 2026 at 12:57:46PM +0900, Sang-Heon Jeon wrote:
> Hi Yury,
> 
> On Thu, Jul 2, 2026 at 5:55 AM Yury Norov <yury.norov@gmail.com> wrote:
> >
> > On Thu, Jul 02, 2026 at 02:18:50AM +0900, Sang-Heon Jeon wrote:
> > > mem_topology_setup() intersects node_possible_map with node_online_map.
> > > Nothing sets node_possible_map before this, so it is NODE_MASK_ALL and
> > > the result is just node_online_map.
> > >
> > > In preparation for changing node_possible_map's initial value,
> > > mem_topology_setup() no longer depends on it.
> > >
> > > No functional change.
> > >
> > > Signed-off-by: Sang-Heon Jeon <ekffu200098@gmail.com>
> > > ---
> > >  arch/powerpc/mm/numa.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
> > > index f4cf3ae036de..2fdecae90a01 100644
> > > --- a/arch/powerpc/mm/numa.c
> > > +++ b/arch/powerpc/mm/numa.c
> > > @@ -1179,7 +1179,7 @@ void __init mem_topology_setup(void)
> > >        * that we expect to make use of for this platform's affinity
> > >        * calculations.
> > >        */
> > > -     nodes_and(node_possible_map, node_possible_map, node_online_map);
> > > +     node_possible_map = node_online_map;
> > >
> > >       find_possible_nodes();
> >
> > And in find_possible_nodes():
> >
> >          for (i = 0; i < max_nodes; i++) {
> >                  if (!node_possible(i))
> >                          node_set(i, node_possible_map);
> >          }
> >
> > So, assuming the code reaches to that point, you unconditionally
> > online all the offlined nodes.
> 
> This loop only sets bits in node_possible_map, not in node_online_map,
> so I can't find how it onlines the offlined nodes unexpectedly. Please
> correct me if I'm wrong or missing something.
> 
> Or are you talking about the case where max_nodes exceeds
> MAX_NUMNODES, which was also noticed by sashiko? I think it is a
> pre-existing issue, and this patch does not affect it.

Oops, sorry, It's my bad. They are nodemask_t, not pointers, so in
"node_possible_map = node_online_map" you copy by value.

Thanks,
Yury