linux-kernel - Re: [patch V2 04/29] parisc: Use lockup_detector

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Date:   Thu, 14 Sep 2017 09:46:39 -0400
From:   Don Zickus <dzickus@...hat.com>
To:     Helge Deller <deller@....de>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Sebastian Siewior <bigeasy@...utronix.de>,
        Nicholas Piggin <npiggin@...il.com>,
        Chris Metcalf <cmetcalf@...lanox.com>,
        Ulrich Obergfell <uobergfe@...hat.com>,
        linux-parisc@...r.kernel.org
Subject: Re: [patch V2 04/29] parisc: Use lockup_detector_stop()

On Thu, Sep 14, 2017 at 10:59:17AM +0200, Helge Deller wrote:
> * Thomas Gleixner <tglx@...utronix.de>:
> > The broken lockup_detector_suspend/resume() interface is going away. Use
> > the new lockup_detector_soft_poweroff() interface to stop the watchdog from
> > the busy looping power off routine.
> > 
> > Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> > Cc: Don Zickus <dzickus@...hat.com>
> > Cc: Chris Metcalf <cmetcalf@...lanox.com>
> > Cc: linux-parisc@...r.kernel.org
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Cc: Sebastian Siewior <bigeasy@...utronix.de>
> > Cc: Nicholas Piggin <npiggin@...il.com>
> > Cc: Ulrich Obergfell <uobergfe@...hat.com>
> > Cc: Borislav Petkov <bp@...en8.de>
> > Cc: Andrew Morton <akpm@...ux-foundation.org>
> > Cc: Helge Deller <deller@....de>
> > Link: http://lkml.kernel.org/r/20170831073053.281414373@linutronix.de
> > 
> > ---
> >  arch/parisc/kernel/process.c |    2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > --- a/arch/parisc/kernel/process.c
> > +++ b/arch/parisc/kernel/process.c
> > @@ -146,7 +146,7 @@ void machine_power_off(void)
> >  
> >  	/* prevent soft lockup/stalled CPU messages for endless loop. */
> >  	rcu_sysrq_start();
> > -	lockup_detector_suspend();
> > +	lockup_detector_soft_poweroff();
> >  	for (;;);
> >  }
> 
> Thomas, thanks for cleaning that up.  
> You may add to patches 03/04:
> Acked-by: Helge Deller <deller@....de>
> 
> 
> On a side-note, there is sadly no general function like
> 	turn_off_all_kind_of_runtime_hang_detectors()
> which turns off *all* detectors at once (including soft lockup detector).
> I've seen another detector complaing at runtime that we were hanging
> here. I would need to dig up more info if you are interested...

There are numerous detectors I have seen over the years: rcu, clocksource,
hard/soft, hang, fs, network, wq?, etc..  I am not sure it is easy to put
them all in one place or makes sense.

I know working with the kvm folks, when they swap back in, the real clock
can do a massive jump forward and causes a flood of warnings such that they
had to 'touch' all of them before running the vm again.

Cheers,
Don