Re: [RFC PATCH v2 07/35] x86: intel_epb: Don't rely on link order

[Gavin Shan]

On 9/14/23 02:37, James Morse wrote:
> intel_epb_init() is called as a subsys_initcall() to register cpuhp
> callbacks. The callbacks make use of get_cpu_device() which will return
> NULL unless register_cpu() has been called. register_cpu() is called
> from topology_init(), which is also a subsys_initcall().
>
> This is fragile. Moving the register_cpu() to a different
> subsys_initcall()  leads to a NULL derefernce during boot.
                                     ^^^^^^^^^^
                                     s/derefernce/dereference

Reported by ./scripts/checkpatch.pl --codespell

> Make intel_epb_init() a late_initcall(), user-space can't provide a
> policy before this point anyway.
>
> Signed-off-by: James Morse <james.morse@xxxxxxx>
> ---
> subsys_initcall_sync() would be an option, but moving the register_cpu()
> calls into ACPI also means adding a safety net for CPUs that are online
> but not described properly by firmware. This lives in subsys_initcall_sync().
> ---
>   arch/x86/kernel/cpu/intel_epb.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kernel/cpu/intel_epb.c b/arch/x86/kernel/cpu/intel_epb.c
> index e4c3ba91321c..f18d35fe27a9 100644
> --- a/arch/x86/kernel/cpu/intel_epb.c
> +++ b/arch/x86/kernel/cpu/intel_epb.c
> @@ -237,4 +237,4 @@ static __init int intel_epb_init(void)
>   	cpuhp_remove_state(CPUHP_AP_X86_INTEL_EPB_ONLINE);
>   	return ret;
>   }
> -subsys_initcall(intel_epb_init);
> +late_initcall(intel_epb_init);

Thanks,
Gavin