On Wed, Mar 30, 2022 at 07:21:23PM +0530, Srikar Dronamraju wrote:
> With commit 09f49dca570a ("mm: handle uninitialized numa nodes
> gracefully") NODE_DATA for even a memoryless/cpuless node is partially
> initialized at boot time.
>
> Before onlining the node, current Powerpc code checks for NODE_DATA to
> be NULL. However since NODE_DATA is partially initialized, this check
> will end up always being false.
>
> This causes hotplugging a CPU to a memoryless/cpuless node to fail.
>
> Before adding CPUs
> $ numactl -H
> available: 1 nodes (4)
> node 4 cpus: 0 1 2 3 4 5 6 7
> node 4 size: 97372 MB
> node 4 free: 95545 MB
> node distances:
> node 4
> 4: 10
>
> $ lparstat
> System Configuration
> type=Dedicated mode=Capped smt=8 lcpu=1 mem=99709440 kB cpus=0 ent=1.00
>
> %user %sys %wait %idle physc %entc lbusy app vcsw phint
> ----- ----- ----- ----- ----- ----- ----- ----- ----- -----
> 2.66 2.67 0.16 94.51 0.00 0.00 5.33 0.00 67749 0
>
> After hotplugging 32 cores
> $ numactl -H
> node 4 cpus: 0 1 2 3 4 5 6 7 120 121 122 123 124 125 126 127 128 129 130
> 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148
> 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166
> 167 168 169 170 171 172 173 174 175
> node 4 size: 97372 MB
> node 4 free: 93636 MB
> node distances:
> node 4
> 4: 10
>
> $ lparstat
> System Configuration
> type=Dedicated mode=Capped smt=8 lcpu=33 mem=99709440 kB cpus=0 ent=33.00
>
> %user %sys %wait %idle physc %entc lbusy app vcsw phint
> ----- ----- ----- ----- ----- ----- ----- ----- ----- -----
> 0.04 0.02 0.00 99.94 0.00 0.00 0.06 0.00 1128751 3
>
> As we can see numactl is listing only 8 cores while lparstat is showing
> 33 cores.
>
> Also dmesg is showing messages like:
> [ 2261.318350 ] BUG: arch topology borken
> [ 2261.318357 ] the DIE domain not a subset of the NODE domain
>
> Fixes: 09f49dca570a ("mm: handle uninitialized numa nodes gracefully")
> Cc: linuxppc-dev@xxxxxxxxxxxxxxxx
> Cc: linux-mm@xxxxxxxxx
> Cc: Michal Hocko <mhocko@xxxxxxxxxx>
> Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
> Reported-by: Geetika Moolchandani <Geetika.Moolchandani1@xxxxxxx>
> Signed-off-by: Srikar Dronamraju <srikar@xxxxxxxxxxxxxxxxxx>
Acked-by: Mike Rapoport <rppt@xxxxxxxxxxxxx>
> ---
> 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 b9b7fefbb64b..13022d734951 100644
> --- a/arch/powerpc/mm/numa.c
> +++ b/arch/powerpc/mm/numa.c
> @@ -1436,7 +1436,7 @@ int find_and_online_cpu_nid(int cpu)
> if (new_nid < 0 || !node_possible(new_nid))
> new_nid = first_online_node;
>
> - if (NODE_DATA(new_nid) == NULL) {
> + if (!node_online(new_nid)) {
> #ifdef CONFIG_MEMORY_HOTPLUG
> /*
> * Need to ensure that NODE_DATA is initialized for a node from
> --
> 2.27.0
>
>
--
Sincerely yours,
Mike.
