Srikar Dronamraju [off-list ref] writes:

* Aneesh Kumar K.V [off-list ref] [2022-06-23 18:24:41]:

quoted

If early cpu to node mapping finds an invalid node id, return
the first online node instead of node 0.

With commit e75130f20b1f ("powerpc/numa: Offline memoryless cpuless node 0")
the kernel marks node 0 offline in certain scenarios.

Signed-off-by: Aneesh Kumar K.V <redacted>
---
 arch/powerpc/include/asm/topology.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/include/asm/topology.h b/arch/powerpc/include/asm/topology.h
index 8a4d4f4d9749..704088b1d53c 100644
--- a/arch/powerpc/include/asm/topology.h
+++ b/arch/powerpc/include/asm/topology.h

@@ -60,7 +60,7 @@ static inline int early_cpu_to_node(int cpu)
 	 * Fall back to node 0 if nid is unset (it should be, except bugs).
 	 * This allows callers to safely do NODE_DATA(early_cpu_to_node(cpu)).
 	 */
-	return (nid < 0) ? 0 : nid;
+	return (nid < 0) ? first_online_node : nid;

Looks good but just two queries.

1. Is there a possibility of early_cpu_to_node() being called before any
node is online?

The kernel operate with node 0 online most of the early boot and mark it offline
in mem_topology_setup() just before parse_numa_properties(). So we
should find some nodes set online.

2. first_online_node is actually not a variable, it returns the lowest
online node. Right? If lets a early_cpu_to_node() for the same CPU across a
node online/offline may end up giving two different nids. Right?

The change is specific to a case where we find uninitialized
numa_cpu_lookup_table. ie, the firmware didn't specify the mapping for
the cpu. I do agree that for such cpus the node mapping can change
because of the above. I am not sure whether this can cause any issue in
practice. But returning node 0 which can be marked offline can result
in crashes? 

quoted

 }

 int of_drconf_to_nid_single(struct drmem_lmb *lmb);
-- 
2.36.1

-- 
Thanks and Regards
Srikar Dronamraju