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

[Joseph Salisbury <joseph.salisbury@canonical.com>]

On 05/06/2016 03:13 PM, Boris Ostrovsky 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@linutronix.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.
> Joe, do you have
>
> ed6069b xen/apic: Provide Xen-specific version of cpu_present_to_apicid
> APIC op
>
> -boris
Yes the commit is in the 4.4 based Ubuntu kernel.  This bug also happens
with the vanilla 4.6-rc5 kernel, which also has that commit.


>
>
>> 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);
>>  
>>  	/*
>