[RFC,v2,25/35] LoongArch: Use the __weak version of arch_unregister_cpu()

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.

Remove arch_unregister_cpu() and use the __weak version.

Signed-off-by: James Morse <james.morse@arm.com>
---
 arch/loongarch/kernel/topology.c | 9 ---------
 1 file changed, 9 deletions(-)

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

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.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

On 9/14/23 02:38, James Morse 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.
> 
> Remove arch_unregister_cpu() and use the __weak version.
> 
> Signed-off-by: James Morse <james.morse@arm.com>
> ---
>   arch/loongarch/kernel/topology.c | 9 ---------
>   1 file changed, 9 deletions(-)
> 
I think arch/x86/kernel/topology.c::arch_unregister_cpu() can be dropped either.

Reviewed-by: Gavin Shan <gshan@redhat.com>

> 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

Thanks,
Gavin