linux-kernel - Re: [Suggestion] about calling debug_hotplug_cpu() which enabled by 'allmodconfig' for a x86

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Date:	Thu, 03 Oct 2013 00:41:45 +0800
From:	Chen Gang F T <chen.gang.flying.transformer@...il.com>
To:	Toshi Kani <toshi.kani@...com>
CC:	Chen Gang <gang.chen@...anux.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	"Yu, Fenghua" <fenghua.yu@...el.com>,
	"rafael.j.wysocki@...el.com" <rafael.j.wysocki@...el.com>,
	"isimatu.yasuaki@...fujitsu.com" <isimatu.yasuaki@...fujitsu.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [Suggestion] about calling debug_hotplug_cpu() which enabled
 by 'allmodconfig' for a x86_64 dual core laptop.

On 10/02/2013 11:28 PM, Toshi Kani wrote:
> On Wed, 2013-10-02 at 03:10 +0000, Chen Gang wrote:
>> Hello Maintainers:
>>
>> Under my x86_64 dual core laptop, I build kernel next-20130927 with
>> 'allmodconfig', and install it, the machine can not start. Related
>> information is:
>>
>>   after call debug_hotplug_cpu(), output "cpu 0 is offline" .... and then "Failed to execute /init".
>>
>> After remove "_debug_hotplug_cpu(0, 0);", can pass the issue (but will
>> fail in another place). I guess, the reason is my laptop cpu is not
>> 'hotplug', but have to call debug_hotplug_cpu() with allmodconfig.
>>
>>
>> I will continue analyzing, welcome any additional suggestions or
>> completions.
> 
> allmodconfig sets CONFIG_DEBUG_HOTPLUG_CPU0 to y (which is defined as
> "def_bool n"), which puts CPU0 offline during boot for testing.  This
> debug feature is causing the problem on your laptop.  I am not familiar
> with allmodconfig, but it seems that it enables all the config options,
> preferably with 'm'.
> 

Hmm... excuse me, I don't know: for laptop, if cpu0 is offline, whether
it still can work or not. If any members know about it, please tell me,
thanks.

In my opinion, if enable DEBUG_HOTPLUG_CPU0, but "should not let cpu0
offline for laptop", we need let 'offline' operation fail.

And I am analyzing (just constructing environments: KVM, kgdb ...),
before let kernel start successfully, only according to my current
proofs, we can not say "let laptop cpu0 offline" must be an issue.

Thanks.

> Thanks,
> -Toshi
> 
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Thanks.
-- 
Chen Gang
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