During the kernel booting, the generic cpu_to_node() is called too early in
arm64, powerpc and riscv when CONFIG_NUMA is enabled.

There are at least four places in the common code where
the generic cpu_to_node() is called before it is initialized:
	   1.) early_trace_init()         in kernel/trace/trace.c
	   2.) sched_init()               in kernel/sched/core.c
	   3.) init_sched_fair_class()    in kernel/sched/fair.c
	   4.) workqueue_init_early()     in kernel/workqueue.c

In order to fix the bug, the patch introduces early_numa_node_init()
which is called after smp_prepare_boot_cpu() in start_kernel.
early_numa_node_init will initialize the "numa_node" as soon as
the early_cpu_to_node() is ready, before the cpu_to_node() is called
at the first time.

Signed-off-by: Huang Shijie <shijie@os.amperecomputing.com>
---
v2 --> v3:
	Do not change the cpu_to_node to function pointer.
	Introduce early_numa_node_init() which initialize
	the numa_node at an early stage.

	v2: https://lore.kernel.org/all/20240123045843.75969-1-shijie@os.amperecomputing.com/
	
v1 --> v2:
	In order to fix the x86 compiling error, move the cpu_to_node()
       	from driver/base/arch_numa.c to driver/base/node.c.

	v1: http://lists.infradead.org/pipermail/linux-arm-kernel/2024-January/896160.html

	An old different title patch:
	http://lists.infradead.org/pipermail/linux-arm-kernel/2024-January/895963.html

---
 init/main.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/init/main.c b/init/main.c
index e24b0780fdff..39efe5ed58a0 100644
--- a/init/main.c
+++ b/init/main.c
@@ -870,6 +870,19 @@ static void __init print_unknown_bootoptions(void)
 	memblock_free(unknown_options, len);
 }
 
+static void __init early_numa_node_init(void)
+{
+#ifdef CONFIG_USE_PERCPU_NUMA_NODE_ID
+#ifndef cpu_to_node
+	int cpu;
+
+	/* The early_cpu_to_node() should be ready here. */
+	for_each_possible_cpu(cpu)
+		set_cpu_numa_node(cpu, early_cpu_to_node(cpu));
+#endif
+#endif
+}
+
 asmlinkage __visible __init __no_sanitize_address __noreturn __no_stack_protector
 void start_kernel(void)
 {
@@ -900,6 +913,7 @@ void start_kernel(void)
 	setup_nr_cpu_ids();
 	setup_per_cpu_areas();
 	smp_prepare_boot_cpu();	/* arch-specific boot-cpu hooks */
+	early_numa_node_init();
 	boot_cpu_hotplug_init();
 
 	pr_notice("Kernel command line: %s\n", saved_command_line);
-- 
2.40.1

On Fri, 26 Jan 2024 14:44:51 +0800 Huang Shijie <shijie@os.amperecomputing.com> wrote:

> During the kernel booting, the generic cpu_to_node() is called too early in
> arm64, powerpc and riscv when CONFIG_NUMA is enabled.
> 
> There are at least four places in the common code where
> the generic cpu_to_node() is called before it is initialized:
> 	   1.) early_trace_init()         in kernel/trace/trace.c
> 	   2.) sched_init()               in kernel/sched/core.c
> 	   3.) init_sched_fair_class()    in kernel/sched/fair.c
> 	   4.) workqueue_init_early()     in kernel/workqueue.c
> 
> In order to fix the bug, the patch introduces early_numa_node_init()
> which is called after smp_prepare_boot_cpu() in start_kernel.
> early_numa_node_init will initialize the "numa_node" as soon as
> the early_cpu_to_node() is ready, before the cpu_to_node() is called
> at the first time.

What are the userspace-visible runtime effects of this bug?

On Wed, 27 Mar 2024, Andrew Morton wrote:

>> In order to fix the bug, the patch introduces early_numa_node_init()
>> which is called after smp_prepare_boot_cpu() in start_kernel.
>> early_numa_node_init will initialize the "numa_node" as soon as
>> the early_cpu_to_node() is ready, before the cpu_to_node() is called
>> at the first time.
>
> What are the userspace-visible runtime effects of this bug?

Performance is reduced since there is increase in off node accesses.

在 2024/3/28 2:17, Andrew Morton 写道:
> On Fri, 26 Jan 2024 14:44:51 +0800 Huang Shijie <shijie@os.amperecomputing.com> wrote:
>
>> During the kernel booting, the generic cpu_to_node() is called too early in
>> arm64, powerpc and riscv when CONFIG_NUMA is enabled.
>>
>> There are at least four places in the common code where
>> the generic cpu_to_node() is called before it is initialized:
>> 	   1.) early_trace_init()         in kernel/trace/trace.c
>> 	   2.) sched_init()               in kernel/sched/core.c
>> 	   3.) init_sched_fair_class()    in kernel/sched/fair.c
>> 	   4.) workqueue_init_early()     in kernel/workqueue.c
>>
>> In order to fix the bug, the patch introduces early_numa_node_init()
>> which is called after smp_prepare_boot_cpu() in start_kernel.
>> early_numa_node_init will initialize the "numa_node" as soon as
>> the early_cpu_to_node() is ready, before the cpu_to_node() is called
>> at the first time.
> What are the userspace-visible runtime effects of this bug?
>
For this bug, I do not see too much performance impact in the userspace 
applications.

It just pollutes the CPU caches in NUMA.


Thanks

Huang Shijie

On Thu, 25 Jan 2024 22:44:51 PST (-0800), shijie@os.amperecomputing.com wrote:
> During the kernel booting, the generic cpu_to_node() is called too early in
> arm64, powerpc and riscv when CONFIG_NUMA is enabled.
>
> There are at least four places in the common code where
> the generic cpu_to_node() is called before it is initialized:
> 	   1.) early_trace_init()         in kernel/trace/trace.c
> 	   2.) sched_init()               in kernel/sched/core.c
> 	   3.) init_sched_fair_class()    in kernel/sched/fair.c
> 	   4.) workqueue_init_early()     in kernel/workqueue.c
>
> In order to fix the bug, the patch introduces early_numa_node_init()
> which is called after smp_prepare_boot_cpu() in start_kernel.
> early_numa_node_init will initialize the "numa_node" as soon as
> the early_cpu_to_node() is ready, before the cpu_to_node() is called
> at the first time.
>
> Signed-off-by: Huang Shijie <shijie@os.amperecomputing.com>
> ---
> v2 --> v3:
> 	Do not change the cpu_to_node to function pointer.
> 	Introduce early_numa_node_init() which initialize
> 	the numa_node at an early stage.
>
> 	v2: https://lore.kernel.org/all/20240123045843.75969-1-shijie@os.amperecomputing.com/
>
> v1 --> v2:
> 	In order to fix the x86 compiling error, move the cpu_to_node()
>        	from driver/base/arch_numa.c to driver/base/node.c.
>
> 	v1: http://lists.infradead.org/pipermail/linux-arm-kernel/2024-January/896160.html
>
> 	An old different title patch:
> 	http://lists.infradead.org/pipermail/linux-arm-kernel/2024-January/895963.html
>
> ---
>  init/main.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
>
> diff --git a/init/main.c b/init/main.c
> index e24b0780fdff..39efe5ed58a0 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -870,6 +870,19 @@ static void __init print_unknown_bootoptions(void)
>  	memblock_free(unknown_options, len);
>  }
>
> +static void __init early_numa_node_init(void)
> +{
> +#ifdef CONFIG_USE_PERCPU_NUMA_NODE_ID
> +#ifndef cpu_to_node
> +	int cpu;
> +
> +	/* The early_cpu_to_node() should be ready here. */
> +	for_each_possible_cpu(cpu)
> +		set_cpu_numa_node(cpu, early_cpu_to_node(cpu));
> +#endif
> +#endif
> +}
> +
>  asmlinkage __visible __init __no_sanitize_address __noreturn __no_stack_protector
>  void start_kernel(void)
>  {
> @@ -900,6 +913,7 @@ void start_kernel(void)
>  	setup_nr_cpu_ids();
>  	setup_per_cpu_areas();
>  	smp_prepare_boot_cpu();	/* arch-specific boot-cpu hooks */
> +	early_numa_node_init();
>  	boot_cpu_hotplug_init();
>
>  	pr_notice("Kernel command line: %s\n", saved_command_line);

Acked-by: Palmer Dabbelt <palmer@rivosinc.com> # RISC-V

I don't really understand the init/main.c stuff all that well, I'm 
adding Andrew as it looks like he's been merging stuff here.