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From:   Thomas Gleixner <tglx@linutronix.de>
To:     Feng Tang <feng.tang@intel.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        "H . Peter Anvin" <hpa@zytor.com>,
        David Woodhouse <dwmw@amazon.co.uk>,
        "Paul E . McKenney" <paulmck@kernel.org>, x86@kernel.org,
        linux-kernel@vger.kernel.org, rui.zhang@intel.com,
        tim.c.chen@intel.com
Subject: Re: [Patch v2 2/2] x86/tsc: use logical_packages as a better
 estimation of socket numbers
In-Reply-To: <ZJhUiO+bdBoLU5WF@feng-clx>
References: <20230613052523.1106821-1-feng.tang@intel.com>
 <20230613052523.1106821-2-feng.tang@intel.com>
 <20230615092021.GE1683497@hirez.programming.kicks-ass.net>
 <ZIwMstkB7CG3pDYu@feng-clx> <87h6qz7et0.ffs@tglx> <87edm36qqb.ffs@tglx>
 <ZJW0gi5oQQbxf8Df@feng-clx> <ZJhUiO+bdBoLU5WF@feng-clx>
Date:   Tue, 27 Jun 2023 13:14:34 +0200
Message-ID: <87r0px40o5.ffs@tglx>
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On Sun, Jun 25 2023 at 22:51, Feng Tang wrote:
> From debug, the reason of the hung/stall is detect_extended_topology_early()
> is called by cpu hotplug after boot, where there is "maxcpus=XXX" setting,
> (#echo 1 > /sys/devices/system/cpu/cpuX/online).
>
> It could be fixed with below patch:
> ----------------------------------------------------------------
> diff --git a/arch/x86/kernel/cpu/topology.c b/arch/x86/kernel/cpu/topology.c
> index 828c1f7edac1..1ff73c8c4972 100644
> --- a/arch/x86/kernel/cpu/topology.c
> +++ b/arch/x86/kernel/cpu/topology.c
> @@ -29,7 +29,7 @@ unsigned int __max_die_per_package __read_mostly = 1;
>  EXPORT_SYMBOL(__max_die_per_package);
>  
>  #ifdef CONFIG_SMP
> -unsigned int apic_to_pkg_shift __ro_after_init;
> +unsigned int apic_to_pkg_shift;

Bah, yes. I missed the early_init() call from init_intel(). I hate that
code with a passion.