Re: [PATCH RESEND V2 ] powerpc/numa: Invalidate numa_cpu_lookup_table on cpu remove

[Tyrel Datwyler <tyreld@linux.vnet.ibm.com>]

On 01/26/2018 11:41 AM, Nathan Fontenot wrote:
> When DLPAR removing a CPU, the unmapping of the cpu from a node in
> unmap_cpu_from_node() should also invalidate the CPUs entry in the
> numa_cpu_lookup_table. There is not a guarantee that on a subsequent
> DLPAR add of the CPU the associativity will be the same and thus
> could be in a different node. Invalidating the entry in the
> numa_cpu_lookup_table causes the associativity to be read from the
> device tree at the time of the add.
> 
> The current behavior of not invalidating the CPUs entry in the
> numa_cpu_lookup_table can result in scenarios where the the topology
> layout of CPUs in the partition does not match the device tree
> or the topology reported by the HMC.
> 
> Signed-off-by: Nathan Fontenot <nfont@linux.vnet.ibm.com>

Reviewed-by: Tyrel Datwyler <tyreld@linux.vnet.ibm.com>

> ---
> 
> Originally sent Dec. 5 2017, no reply, resending.
> 
> Updates for V2: Move the invalidation from unmap_cpu_from_node to
> pseries_remove_processor, the former routine is also called during cpu
> offline and we do not want to invalidate during cpu offline.
> 
>  arch/powerpc/include/asm/topology.h          |    5 +++++
>  arch/powerpc/mm/numa.c                       |    5 -----
>  arch/powerpc/platforms/pseries/hotplug-cpu.c |    2 ++
>  3 files changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/topology.h b/arch/powerpc/include/asm/topology.h
> index 88187c285c70..1c02e6900f78 100644
> --- a/arch/powerpc/include/asm/topology.h
> +++ b/arch/powerpc/include/asm/topology.h
> @@ -44,6 +44,11 @@ extern int sysfs_add_device_to_node(struct device *dev, int nid);
>  extern void sysfs_remove_device_from_node(struct device *dev, int nid);
>  extern int numa_update_cpu_topology(bool cpus_locked);
> 
> +static inline void update_numa_cpu_lookup_table(unsigned int cpu, int node)
> +{
> +	numa_cpu_lookup_table[cpu] = node;
> +}
> +
>  static inline int early_cpu_to_node(int cpu)
>  {
>  	int nid;
> diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
> index 268c7a2d9a5b..7ec3a0d787d3 100644
> --- a/arch/powerpc/mm/numa.c
> +++ b/arch/powerpc/mm/numa.c
> @@ -143,11 +143,6 @@ static void reset_numa_cpu_lookup_table(void)
>  		numa_cpu_lookup_table[cpu] = -1;
>  }
> 
> -static void update_numa_cpu_lookup_table(unsigned int cpu, int node)
> -{
> -	numa_cpu_lookup_table[cpu] = node;
> -}
> -
>  static void map_cpu_to_node(int cpu, int node)
>  {
>  	update_numa_cpu_lookup_table(cpu, node);
> diff --git a/arch/powerpc/platforms/pseries/hotplug-cpu.c b/arch/powerpc/platforms/pseries/hotplug-cpu.c
> index a7d14aa7bb7c..09083ad82f7a 100644
> --- a/arch/powerpc/platforms/pseries/hotplug-cpu.c
> +++ b/arch/powerpc/platforms/pseries/hotplug-cpu.c
> @@ -36,6 +36,7 @@
>  #include <asm/xics.h>
>  #include <asm/xive.h>
>  #include <asm/plpar_wrappers.h>
> +#include <asm/topology.h>
> 
>  #include "pseries.h"
>  #include "offline_states.h"
> @@ -331,6 +332,7 @@ static void pseries_remove_processor(struct device_node *np)
>  			BUG_ON(cpu_online(cpu));
>  			set_cpu_present(cpu, false);
>  			set_hard_smp_processor_id(cpu, -1);
> +			update_numa_cpu_lookup_table(cpu, -1);
>  			break;
>  		}
>  		if (cpu >= nr_cpu_ids)
>