linux-kernel - Re: [v4.6-rc1 Regression] x86/topology: Create logical package id

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Message-ID: <572D0385.9050407@canonical.com>
Date:	Fri, 6 May 2016 16:50:13 -0400
From:	Joseph Salisbury <joseph.salisbury@...onical.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	"Peter Zijlstra (Intel)" <peterz@...radead.org>,
	Andi Kleen <andi.kleen@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andy Lutomirski <luto@...capital.net>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Brian Gerst <brgerst@...il.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Harish Chegondi <harish.chegondi@...el.com>,
	Jacob Pan <jacob.jun.pan@...ux.intel.com>,
	Jiri Olsa <jolsa@...hat.com>, Kan Liang <kan.liang@...el.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Luis R. Rodriguez" <mcgrof@...e.com>,
	Stephane Eranian <eranian@...gle.com>,
	Toshi Kani <toshi.kani@...com>,
	Vince Weaver <vincent.weaver@...ne.edu>,
	LKML <linux-kernel@...r.kernel.org>, yingying.zhao@...el.com,
	"Zhang, Xiong Y" <xiong.y.zhang@...el.com>,
	1573231@...s.launchpad.net, 1397880@...s.launchpad.net,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Chen Yucong <slaoub@...il.com>,
	Laura Abbott <labbott@...oraproject.org>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	David Vrabel <david.vrabel@...rix.com>
Subject: Re: [v4.6-rc1 Regression] x86/topology: Create logical package id

On 05/06/2016 03:38 PM, Joseph Salisbury wrote:
> On 05/06/2016 02:48 PM, Thomas Gleixner wrote:
>> On Fri, 6 May 2016, Joseph Salisbury wrote:
>>> A kernel bug report was opened against Ubuntu [0].  After a kernel
>>> bisect, it was found that reverting the following commit resolved this bug:
>>>
>>> commit 1f12e32f4cd5243ae46d8b933181be0d022c6793
>>> Author: Thomas Gleixner <tglx@...utronix.de>
>>> Date:   Mon Feb 22 22:19:15 2016 +0000
>>>
>>>     x86/topology: Create logical package id
>>>
>>> To build successfully with this commit reverted, I also had to revert
>>> commits: e7ee3e8,2d4de83,87f01cc and 33c3cc7.
>>>
>>> The regression was introduced as of v4.6-rc1.
>>>     
>>> I was hoping to get your feedback, since you are the patch author.  Do
>>> you think gathering any additional data will help diagnose this issue,
>>> or would it be best to submit a revert request?
>> Yuck. That dies with a divide error. And that looks like XEN is supplying crap
>> data in the CPUID.
>>
>> Does the patch below cure the issue?
>>
>> Thanks,
>>
>>         tglx
>>
>> 8<---------------
>>
>> --- a/arch/x86/kernel/smpboot.c
>> +++ b/arch/x86/kernel/smpboot.c
>> @@ -332,6 +332,11 @@ static void __init smp_init_package_map(
>>  	 * primary cores.
>>  	 */
>>  	ncpus = boot_cpu_data.x86_max_cores;
>> +	if (!ncpus) {
>> +		pr_warn("x86_max_cores == zero !?!?");
>> +		ncpus = 1;
>> +	}
>> +
>>  	__max_logical_packages = DIV_ROUND_UP(total_cpus, ncpus);
>>  
>>  	/*
> I'll have this patch tested and report back.
>
> Thanks,
>
> Joe
Yes, your patch does in fact fix the bug.  Would you like any additional
information regarding the bug?