linux-kernel - Re: [RFC PATCH v2 25/35] LoongArch: Use the __weak version of arch_unregister

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Message-ID: <20230914154111.0000189d@Huawei.com>
Date:   Thu, 14 Sep 2023 15:41:11 +0100
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
To:     James Morse <james.morse@....com>
CC:     <linux-pm@...r.kernel.org>, <loongarch@...ts.linux.dev>,
        <linux-acpi@...r.kernel.org>, <linux-arch@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-riscv@...ts.infradead.org>, <kvmarm@...ts.linux.dev>,
        <x86@...nel.org>, Salil Mehta <salil.mehta@...wei.com>,
        Russell King <linux@...linux.org.uk>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        <jianyong.wu@....com>, <justin.he@....com>
Subject: Re: [RFC PATCH v2 25/35] LoongArch: Use the __weak version of
 arch_unregister_cpu()

On Wed, 13 Sep 2023 16:38:13 +0000
James Morse <james.morse@....com> wrote:

> LoongArch provides its own arch_unregister_cpu(). This clears the
> hotpluggable flag, then unregisters the CPU.
> 
> It isn't necessary to clear the hotpluggable flag when unregistering
> a cpu. unregister_cpu() writes NULL to the percpu cpu_sys_devices
> pointer, meaning cpu_is_hotpluggable() will return false, as
> get_cpu_device() has returned NULL.

Thought that looked odd earlier but didn't care enough to dig.
Seem unlikely state would persist for an unregistered cpu.
Great to see confirmation.

> 
> Remove arch_unregister_cpu() and use the __weak version.
> 
> Signed-off-by: James Morse <james.morse@....com>

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>


> ---
>  arch/loongarch/kernel/topology.c | 9 ---------
>  1 file changed, 9 deletions(-)
> 
> diff --git a/arch/loongarch/kernel/topology.c b/arch/loongarch/kernel/topology.c
> index 8e4441c1ff39..5a75e2cc0848 100644
> --- a/arch/loongarch/kernel/topology.c
> +++ b/arch/loongarch/kernel/topology.c
> @@ -16,13 +16,4 @@ int arch_register_cpu(int cpu)
>  	return register_cpu(c, cpu);
>  }
>  EXPORT_SYMBOL(arch_register_cpu);
> -
> -void arch_unregister_cpu(int cpu)
> -{
> -	struct cpu *c = &per_cpu(cpu_devices, cpu);
> -
> -	c->hotpluggable = 0;
> -	unregister_cpu(c);
> -}
> -EXPORT_SYMBOL(arch_unregister_cpu);
>  #endif