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

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Date:   Tue, 26 Sep 2023 09:04:46 +1000
From:   Gavin Shan <gshan@...hat.com>
To:     "Russell King (Oracle)" <rmk+kernel@...linux.org.uk>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     linux-acpi@...r.kernel.org, James Morse <james.morse@....com>,
        loongarch@...ts.linux.dev, linux-arch@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        jianyong.wu@....com, justin.he@....com,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        Salil Mehta <salil.mehta@...wei.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-ia64@...r.kernel.org
Subject: Re: [PATCH] cpu-hotplug: provide prototypes for arch CPU registration

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@...linux.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