linux-kernel - Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups

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Message-ID: <alpine.DEB.2.20.1706221730520.1885@nanos>
Date:   Thu, 22 Jun 2017 17:33:02 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Kan Liang <kan.liang@...el.com>
cc:     LKML <linux-kernel@...r.kernel.org>, dzickus@...hat.com,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        babu.moger@...cle.com, atomlin@...hat.com,
        Prarit Bhargava <prarit@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>, eranian@...gle.com,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        ak@...ux.intel.com, stable@...r.kernel.org
Subject: Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups

On Wed, 21 Jun 2017, Thomas Gleixner wrote:

> On Wed, 21 Jun 2017, kan.liang@...el.com wrote:
> > We now have more and more systems where the Turbo range is wide enough
> > that the NMI watchdog expires faster than the soft watchdog timer that
> > updates the interrupt tick the NMI watchdog relies on.
> > 
> > This problem was originally added by commit 58687acba592
> > ("lockup_detector: Combine nmi_watchdog and softlockup detector").
> > Previously the NMI watchdog would always check jiffies, which were
> > ticking fast enough. But now the backing is quite slow so the expire
> > time becomes more sensitive.
> 
> And slapping a factor 3 on the NMI period is the wrong answer to the
> problem. The simple solution would be to increase the hrtimer frequency,
> but that's not really desired either.

Thinking a bit more about it. Increasing the hrtimer frequency and
maintaining the current frequency of softlockup_watchdog wakeups, would be
probably the most trivial workaround for now.

Thanks,

	tglx