Re: [3.14] core onlining/hotplug regression

[Daniel J Blueman <daniel@numascale.com>]

On 07/25/2014 05:05 PM, Thomas Gleixner wrote:
> On Fri, 25 Jul 2014, Daniel J Blueman wrote:
>> On a larger x86 system with 1728 cores, 3.15(.6) asserts on
>> smpboot_thread_fn's td->cpu != smp_processor_id() consistently after ~1500
>> cores are online.
>>
>> Reverting the only directly related changes I could find [1,2] doesn't help.
>> Debugging indicates there is a race where the created thread is quickly
>> migrated to core 0 when this occurs, since smp_processor_id returns 0 in these
>> cases. Thomas introduced a thread parked state to fix related issues a year
>> back. Linux 3.14(.13) boots just nice.
>
> Weird. Commits [1,2] are definitely not the culprits.
>
>> Full boot output is at:
>> https://resources.numascale.com/linux-315-thread-mig.txt
>
> Not really helpful, as we don't see what causes it. We just see the
> wreckage.
>
>> Any theories so far? I'll start bisecting when I have full access to the
>> system again in a week and I'll do some more debugging with intermittent
>> access before then.
>
> One thing you could try is enabling tracing.
>
>      "ftrace=function ftrace_dump_on_oops"
>
> It'll take a looooong time to spill out the traces, but that should
> give us the root cause precisely.

Good trick. I'll get this early next week and we'll see what's up.

Thanks,
   Daniel
-- 
Daniel J Blueman
Principal Software Engineer, Numascale