linux-kernel - Re: [tip:x86/bsp-hotplug] x86, apic: Disable BSP if boot cpu is AP

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Date:	Mon, 11 Nov 2013 11:54:00 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ingo Molnar <mingo@...nel.org>
CC:	linux-kernel@...r.kernel.org, tglx@...utronix.de,
	d.hatayama@...fujitsu.com, hpa@...ux.intel.com,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/bsp-hotplug] x86, apic: Disable BSP if boot cpu is AP

On 10/12/2013 10:42 AM, Ingo Molnar wrote:
> 
> * H. Peter Anvin <hpa@...or.com> wrote:
> 
>> On 10/09/2013 04:16 PM, tip-bot for HATAYAMA Daisuke wrote:
>>> Commit-ID:  1d79e607332d67d9132c176d99b5e7fabe1b6b7f
>>> Gitweb:     http://git.kernel.org/tip/1d79e607332d67d9132c176d99b5e7fabe1b6b7f
>>> Author:     HATAYAMA Daisuke <d.hatayama@...fujitsu.com>
>>> AuthorDate: Thu, 29 Aug 2013 18:28:04 +0900
>>> Committer:  H. Peter Anvin <hpa@...ux.intel.com>
>>> CommitDate: Wed, 9 Oct 2013 15:41:11 -0700
>>>
>>> x86, apic: Disable BSP if boot cpu is AP
>>
>> This patch seems to trigger build failures in some configurations.
>> Specifically:
>>
>> (.init.text+0x1307): undefined reference to `boot_cpu_is_bsp_init'
>>
>> Unfortunately I don't have the specific configuration which triggers the 
>> failure, as this was discovered by Fengguang's robot.
> 
> I have triggered that too and have such a config, it's attached.

Okay, thinking about this again, this patchset is in fact broken on:

1. Any configuration which has CONFIG_SMP=n and CONFIG_X86_UP_APIC=n.

This is a built-time problem.

2. Any CPU which is old enough that MSR_IA32_APICBASE doesn't exist.

This is a fatal runtime bug.

3. Any clustered solution which involves a third-party cluster
controller such that MSR_IA32_APICBASE may not reflect the reality of
the system.

This is a less critical issue as "all" it ought to make happen is to
disable some CPUs which didn't need it.

Hatayama-san, you got this build bug report almost a month ago.  It
looks like it is going to need a fair bit of cleanup, so I fear this is
going to be dropped for v3.13.

	-hpa

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