Date: Wed, 1 Mar 2017 23:34:18 +0100 (CET)
From: Thomas Gleixner <tglx@linutronix.de>
To: Meelis Roos <mroos@linux.ee>
cc: Linux Kernel list <linux-kernel@vger.kernel.org>, x86@kernel.org,
        Peter Zijlstra <peterz@infradead.org>
Subject: Re: PPro arch_cpu_idle: NMI watchdog: Watchdog detected hard LOCKUP
 on cpu 1
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References: <alpine.LRH.2.20.1703011719350.22226@math.ut.ee> <alpine.DEB.2.20.1703011801420.4005@nanos> <alpine.LRH.2.20.1703020006260.1113@math.ut.ee>
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On Thu, 2 Mar 2017, Meelis Roos wrote:

> > > This is on my trusty IBM PC365, dual Pentium Pro. 4.10 worked fine, 
> > > 4.10.0-09686-g9e314890292c and 4.10.0-10770-g2d6be4abf514 exhibit a 
> > > problem. Ocassionally NMI watchdog kicks in and discovers one of the 
> > > CPUs in LOCKUP. The system keeps running fine. The first lockup was 
> > > different, all the others were from arch_cpu_idle. Sometime ecey couple 
> > > of seconds (after some activity), sometimes nothing for a long time 
> > > (idle, no SSH logins).
> > 
> > The only watchdog related patch which hit after 4.10 is:
> > 
> >  8dcde9def5a1 kernel/watchdog.c: do not hardcode CPU 0 as the initial thread
> > 
> > Can you try to revert that for a start? I'm not seeing why it should be the
> > culprit from a quick glance, but ...
> 
> Reverting this patch does not help.

I did not expect that, but excluding it was a valid shot in the
dark. Thanmks for trying.

To be honest, I have no idea what causes that at the moment, but I will
come back to you tomorrow after thinking it through (with brain awake) how
to debug this.

Thanks,

	tglx