linux-kernel - Re: [PATCH RFC 02/22] x86: intel

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Message-ID: <20231128144059.000042c8@Huawei.com>
Date:   Tue, 28 Nov 2023 14:40:59 +0000
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
To:     Russell King <rmk+kernel@...linux.org.uk>
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>, <linux-csky@...r.kernel.org>,
        <linux-doc@...r.kernel.org>, <linux-ia64@...r.kernel.org>,
        <linux-parisc@...r.kernel.org>,
        Salil Mehta <salil.mehta@...wei.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        <jianyong.wu@....com>, <justin.he@....com>,
        James Morse <james.morse@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH RFC 02/22] x86: intel_epb: Don't rely on link order

On Tue, 07 Nov 2023 10:29:28 +0000
Russell King <rmk+kernel@...linux.org.uk> wrote:

> From: James Morse <james.morse@....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@....com>
> Signed-off-by: Russell King (Oracle) <rmk+kernel@...linux.org.uk>

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

> ---
> 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);