linux-kernel - Re: REGRESSION: boot stalls on several old dual core Intel CPUs

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Message-ID: <alpine.DEB.2.21.1809030937230.1349@nanos.tec.linutronix.de>
Date:   Mon, 3 Sep 2018 09:38:15 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>
cc:     Kevin Shanahan <kevin@...nahan.id.au>,
        Siegfried Metz <frame@...lbox.org>,
        linux-kernel@...r.kernel.org, rafael.j.wysocki@...el.com,
        len.brown@...el.com, rjw@...ysocki.net, diego.viola@...il.com,
        rui.zhang@...el.com, viktor_jaegerskuepper@...enet.de
Subject: Re: REGRESSION: boot stalls on several old dual core Intel CPUs

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@...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