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Date:   Mon, 3 Sep 2018 09:38:15 +0200 (CEST)
From:   Thomas Gleixner <tglx@linutronix.de>
To:     Peter Zijlstra <peterz@infradead.org>
cc:     Kevin Shanahan <kevin@shanahan.id.au>,
        Siegfried Metz <frame@mailbox.org>,
        linux-kernel@vger.kernel.org, rafael.j.wysocki@intel.com,
        len.brown@intel.com, rjw@rjwysocki.net, diego.viola@gmail.com,
        rui.zhang@intel.com, viktor_jaegerskuepper@freenet.de
Subject: Re: REGRESSION: boot stalls on several old dual core Intel CPUs
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On Mon, 3 Sep 2018, Peter Zijlstra wrote:
> On Sat, Sep 01, 2018 at 11:51:26AM +0930, Kevin Shanahan wrote:
> > commit 01548f4d3e8e94caf323a4f664eb347fd34a34ab
> > Author: Martin Schwidefsky <schwidefsky@de.ibm.com>
> > Date:   Tue Aug 18 17:09:42 2009 +0200
> > 
> >     clocksource: Avoid clocksource watchdog circular locking dependency
> > 
> >     stop_machine from a multithreaded workqueue is not allowed because
> >     of a circular locking dependency between cpu_down and the workqueue
> >     execution. Use a kernel thread to do the clocksource downgrade.
> 
> I cannot find stop_machine usage there; either it went away or I need to
> like wake up.

timekeeping_notify() which is involved in switching clock source uses stomp
machine.

Thanks,

	tglx