linux-kernel - [3.14] core onlining/hotplug regression

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Date:	Fri, 25 Jul 2014 15:50:06 +0800
From:	Daniel J Blueman <daniel@...ascale.com>
To:	Oleg Nesterov <oleg@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Hillf Danton <dhillf@...il.com>
CC:	Borislav Petkov <bp@...64.org>, Ingo Molnar <mingo@...hat.com>,
	Igor Mammedov <imammedo@...hat.com>,
	Steffen Persvold <sp@...ascale.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: [3.14] core onlining/hotplug regression

Hi Thomas et al,

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.

Full boot output is at:
https://resources.numascale.com/linux-315-thread-mig.txt

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.

Thanks,
   Daniel

-- [1]

commit 81c98869faa5f3a9457c93efef908ef476326b31
Author: Nishanth Aravamudan <nacc@...ux.vnet.ibm.com>
Date:   Thu Apr 3 14:46:25 2014 -0700
kthread: ensure locality of task_struct allocations

-- [2]

commit 89f898c1e195fa6235c869bb457e500b7b3ac49d
Author: Igor Mammedov <imammedo@...hat.com>
Date:   Thu Jun 5 15:42:43 2014 +0200

     x86: Fix list/memory corruption on CPU hotplug
-- 
Daniel J Blueman
Principal Software Engineer, Numascale
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