On Wed, Aug 24, 2016 at 04:26:49PM -0700, Tim Chen wrote:
> In current kernel code, we only call node_set_state(cpu_to_node(cpu),
> N_CPU) when a cpu is hot plugged. But we do not set the node state for
> N_CPU when the cpus are brought online during boot.
>
> So this could lead to failure when we check to see
> if a node contains cpu with node_state(node_id, N_CPU).
>
> One use case is in the node_reclaime function:
>
> /*
> * Only run node reclaim on the local node or on nodes that do
> * not
> * have associated processors. This will favor the local
> * processor
> * over remote processors and spread off node memory allocations
> * as wide as possible.
> */
> if (node_state(pgdat->node_id, N_CPU) && pgdat->node_id !=
> numa_node_id())
> return NODE_RECLAIM_NOSCAN;
>
> I instrumented the kernel to call this function after boot and it
> always returns 0 on a x86 desktop machine until I apply
> the attached patch.
>
> static int num_cpu_node(void)
> {
> int i, nr_cpu_nodes = 0;
>
> for_each_node(i) {
> if (node_state(i, N_CPU))
> ++ nr_cpu_nodes;
> }
>
> return nr_cpu_nodes;
> }
>
> I have not tested other architectues but they are likely
> to have similar issue.
>
> Signed-off-by: Tim Chen <[email protected]>
> ---
> arch/x86/kernel/smpboot.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
> index d8f7d01..04c0574 100644
> --- a/arch/x86/kernel/smpboot.c
> +++ b/arch/x86/kernel/smpboot.c
> @@ -259,6 +259,7 @@ static void notrace start_secondary(void *unused)
> lock_vector_lock();
> setup_vector_irq(smp_processor_id());
> set_cpu_online(smp_processor_id(), true);
> + node_set_state(cpu_to_node(smp_processor_id()), N_CPU);
> unlock_vector_lock();
> cpu_set_state_online(smp_processor_id());
> x86_platform.nmi_init();
Would it not be easier to register the vmstat_notifier earlier, before
SMP bringup? Because with this change, we need to go fix all
architectures.
