Re: [3.14] core onlining/hotplug regression

From: Daniel J Blueman
Date: Fri Jul 25 2014 - 05:37:24 EST

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:

Not really helpful, as we don't see what causes it. We just see the

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.

Daniel J Blueman
Principal Software Engineer, Numascale
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