Comment 23 for bug 1573231

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 <email address hidden>
>> 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