[PATCH 02/21] x86: intel_epb: Don't rely on link order

[Rafael J. Wysocki]

On Tue, Nov 21, 2023 at 2:44 PM Russell King <rmk+kernel at armlinux.org.uk> wrote:
>
> From: James Morse <james.morse at arm.com>
>
> 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 dereference during boot.
>
> 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 at arm.com>
> Reviewed-by: Gavin Shan <gshan at redhat.com>
> Signed-off-by: Russell King (Oracle) <rmk+kernel at armlinux.org.uk>

Acked-by: Rafael J. Wysocki <rafael.j.wysocki at intel.com>

and I'd suggest sending this separately to the x86 list.

> ---
> 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);
> --
> 2.30.2
>
>