Re: [PATCH] cpu-hotplug: provide prototypes for arch CPU registration

Gavin Shan
2023-09-25T23:05:47Z

Hi Russell,

On 9/26/23 02:28, Russell King (Oracle) wrote:
> Provide common prototypes for arch_register_cpu() and
> arch_unregister_cpu(). These are called by acpi_processor.c, with
> weak versions, so the prototype for this is already set. It is
> generally not necessary for function prototypes to be conditional
> on preprocessor macros.
>
> Some architectures (e.g. Loongarch) are missing the prototype for this,
> and rather than add it to Loongarch's asm/cpu.h, lets do the job once
> for everyone.
>
> Since this covers everyone, remove the now unnecessary prototypes in
> asm/cpu.h, and we also need to remove the 'static' from one of ia64's
> arch_register_cpu() definitions.
>
> Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
> ---
> Changes since RFC v2:
> - drop ia64 changes, as ia64 has already been removed.
>
> arch/x86/include/asm/cpu.h | 2 --
> arch/x86/kernel/topology.c | 2 +-
> include/linux/cpu.h | 2 ++
> 3 files changed, 3 insertions(+), 3 deletions(-)
>

In Linux 6.6.rc3, the prototypes are still existing in arch/ia64/include/asm/cpu.h.
They may have been dropped in other ia64 or x86 git repository, which this patch
bases on.

In the commit message, 'static' from one of ia64's arch_register_cpu() definitions
is removed, but there is no changes related to ia64 in this patch. I guess that's
probably x86?

> diff --git a/arch/x86/include/asm/cpu.h b/arch/x86/include/asm/cpu.h
> index 3a233ebff712..25050d953eee 100644
> --- a/arch/x86/include/asm/cpu.h
> +++ b/arch/x86/include/asm/cpu.h
> @@ -28,8 +28,6 @@ struct x86_cpu {
> };
>
> #ifdef CONFIG_HOTPLUG_CPU
> -extern int arch_register_cpu(int num);
> -extern void arch_unregister_cpu(int);
> extern void soft_restart_cpu(void);
> #endif
>
> diff --git a/arch/x86/kernel/topology.c b/arch/x86/kernel/topology.c
> index ca004e2e4469..0bab03130033 100644
> --- a/arch/x86/kernel/topology.c
> +++ b/arch/x86/kernel/topology.c
> @@ -54,7 +54,7 @@ void arch_unregister_cpu(int num)
> EXPORT_SYMBOL(arch_unregister_cpu);
> #else /* CONFIG_HOTPLUG_CPU */
>
> -static int __init arch_register_cpu(int num)
> +int __init arch_register_cpu(int num)
> {
> return register_cpu(&per_cpu(cpu_devices, num).cpu, num);
> }

I think arch/ia64/kernel/topology.c may need same change, as stated in the commit log.
In linux 6.6.rc3, 'static' exists in arch/ia64/kernel/topology.c::arch_register_cpu().
Again, your patch may have been based on other git repository.

> diff --git a/include/linux/cpu.h b/include/linux/cpu.h
> index 0abd60a7987b..eb768a866fe3 100644
> --- a/include/linux/cpu.h
> +++ b/include/linux/cpu.h
> @@ -80,6 +80,8 @@ extern __printf(4, 5)
> struct device *cpu_device_create(struct device *parent, void *drvdata,
> const struct attribute_group **groups,
> const char *fmt, ...);
> +extern int arch_register_cpu(int cpu);
> +extern void arch_unregister_cpu(int cpu);
> #ifdef CONFIG_HOTPLUG_CPU
> extern void unregister_cpu(struct cpu *cpu);
> extern ssize_t arch_cpu_probe(const char *, size_t);

Thanks,
Gavin