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    SubjectRe: [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@armlinux.org.uk> wrote:

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

    Seems reasonable. FWIW
    Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.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);

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