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Date: Fri, 20 Oct 2017 20:14:24 +0200 (CEST)
From: Thomas Gleixner <tglx@linutronix.de>
To: Tvrtko Ursulin <tursulin@ursulin.net>
cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>
Subject: Re: Possible bug in CPU hotplug handling (4.14.0-rc5)
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On Fri, 20 Oct 2017, Tvrtko Ursulin wrote:
 
> Hi all,
> 
> I think I've found in bug in the CPU hotplug handling when multi-instance
> states are used. That is in the 4.14.0-rc5 kernel.

> I have not attempted to get to the bottom of the issue to propose an actual
> fix, since the logic there looks somewhat complex, but thought to first
> seek opinion of the people in the know regarding this area.

These commits fiddled with that post rc1, so it's probably burried
somewhere there.

1db49484f21e ("smp/hotplug: Hotplug state fail injection")
5ebe7742fff8 ("smp/hotplug: Differentiate the AP completion between up and down")
5f4b55e10645 ("smp/hotplug: Differentiate the AP-work lockdep class between up and down")
724a86881d03 ("smp/hotplug: Callback vs state-machine consistency")
4dddfb5faa61 ("smp/hotplug: Rewrite AP state machine core")
96abb968549c ("smp/hotplug: Allow external multi-instance rollback")

I'll have a look at it on sunday (tomorrow I'm conferencing) with Peter, so
we should be able to figure it out, unless you beat us to it.

Thanks,

	tglx