[PATCH] pseries/hotplug: Add CPU-to-node mappings for all present CPUs

[PATCH] pseries/hotplug: Add CPU-to-node mappings for all present CPUs

[Srikar Dronamraju]

When cores are added while the system is running in a lower SMT mode,
some threads of those cores remain offline. Moving the system to a
higher SMT mode later fails to online those threads.

For example, on a system with four cores:

  1. ppc64_cpu --smt=off
  2. nproc
       expected: 4
  3. ppc64_cpu --smt
       expected/actual: "SMT is off"
  4. drmgr -c cpu -a -q 4
  5. ppc64_cpu --smt
       expected/actual: "SMT is off"
  6. ppc64_cpu --smt=8
  7. ppc64_cpu --smt
       expected: SMT=8
       actual:   SMT=1: 4-7; SMT=8: 0-3
  8. nproc
       expected: 64
       actual:   36

Post commit d1099e2276df ("powerpc/pseries: Honour current SMT state
when DLPAR onlining CPUs"), when new CPUs are added, the CPU-to-node
mapping is currently updated only for CPUs that are immediately onlined.
CPUs that are made present but remain offline due to the current SMT
mode therefore do not get a CPU-to-node mapping.

When those CPUs are subsequently onlined after switching to a higher
SMT mode, the online operation fails because the required CPU-to-node
mapping is missing.

Update the CPU-to-node mapping before applying the SMT restrictions so
that all newly present CPUs have a node mapping, including CPUs that
remain offline in the current SMT mode.

Fixes: d1099e2276df ("powerpc/pseries: Honour current SMT state when DLPAR onlining CPUs")
Reported-by: Samir Mulani <samir@linux.ibm.com>
Signed-off-by: Srikar Dronamraju <srikar@linux.ibm.com>
---
 arch/powerpc/platforms/pseries/hotplug-cpu.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/platforms/pseries/hotplug-cpu.c b/arch/powerpc/platforms/pseries/hotplug-cpu.c
index bc6926dbf148..b5dc942eec63 100644
--- a/arch/powerpc/platforms/pseries/hotplug-cpu.c
+++ b/arch/powerpc/platforms/pseries/hotplug-cpu.c
@@ -402,6 +402,7 @@ static int dlpar_online_cpu(struct device_node *dn)
 			if (get_hard_smp_processor_id(cpu) != thread)
 				continue;
 
+			find_and_update_cpu_nid(cpu);
 			if (!topology_is_primary_thread(cpu)) {
 				if (cpu_smt_control != CPU_SMT_ENABLED)
 					break;
@@ -410,7 +411,6 @@ static int dlpar_online_cpu(struct device_node *dn)
 			}
 
 			cpu_maps_update_done();
-			find_and_update_cpu_nid(cpu);
 			rc = device_online(get_cpu_device(cpu));
 			if (rc) {
 				dlpar_offline_cpu(dn);
-- 
2.43.7