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

From Don Zickus <dzickus@redhat.com>
Newsgroups linux.kernel
Subject Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups
Date 2017-06-29 17:50 +0200
Message-ID <tXJRE-XD-25@gated-at.bofh.it> (permalink)
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On Wed, Jun 28, 2017 at 01:14:04PM -0700, Andi Kleen wrote:
> It can be a useful debugging tool for a specific class of bugs: 
> when kernel software is looping forever.
> 
> But if that happens does it really matter how many iterations the
> loop does before it is stopped?
> 
> Even the current timeout is essentially eternity in CPU time, and 3x
> eternity is still eternity.

That isn't true.  We have customers that test the accuracy and file bugs.  I
had to write a RHEL whitepaper a number of years ago explaining why the
softlockup took 62 seconds to fire instead of 60.

Customers were changing the watchdog_thresh when the system slowed down to
purposely trigger a panic (which exposed race conditions leading Uli to
redesign the sysctl interface).

I don't feel like explaining to our customers how we regressed on our
watchdog accuracy.  It is exhausting, especially if it is a debug feature.

> 
> > The hrtimer increase maintains that and just adds a few more
> > interrupts/second.
> 
> Interruptions are a big deal for many people.

Yes, and we probably have customers that will complain on that too.

Either solution is a lose/lose.  And yes, we will probably get bit by the
false NMI problems on those Intel boxes.  This is why I was preferring a
real solution.

The question is, if the real solution is going to take a while, what is the
least sucky solution for now?  Or how do we minimize it to a specific class
of Intel boxes.

Cheers,
Don

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Thread

[PATCH V2] kernel/watchdog: fix spurious hard lockups kan.liang@intel.com - 2017-06-21 16:50 +0200
  Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups Thomas Gleixner <tglx@linutronix.de> - 2017-06-21 17:20 +0200
    RE: [PATCH V2] kernel/watchdog: fix spurious hard lockups "Liang, Kan" <kan.liang@intel.com> - 2017-06-21 19:10 +0200
      Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups Prarit Bhargava <prarit@redhat.com> - 2017-06-21 19:50 +0200
    Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups Andi Kleen <ak@linux.intel.com> - 2017-06-21 19:10 +0200
      Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups Thomas Gleixner <tglx@linutronix.de> - 2017-06-21 22:10 +0200
  Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups Thomas Gleixner <tglx@linutronix.de> - 2017-06-22 00:00 +0200
    Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups Thomas Gleixner <tglx@linutronix.de> - 2017-06-22 17:40 +0200
    Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups Don Zickus <dzickus@redhat.com> - 2017-06-22 17:50 +0200
      RE: [PATCH V2] kernel/watchdog: fix spurious hard lockups "Liang, Kan" <kan.liang@intel.com> - 2017-06-22 18:00 +0200
      Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups Thomas Gleixner <tglx@linutronix.de> - 2017-06-23 10:10 +0200
        Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups Don Zickus <dzickus@redhat.com> - 2017-06-23 18:30 +0200
          Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups Thomas Gleixner <tglx@linutronix.de> - 2017-06-24 00:00 +0200
            Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups Don Zickus <dzickus@redhat.com> - 2017-06-26 22:30 +0200
              Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups Thomas Gleixner <tglx@linutronix.de> - 2017-06-26 22:40 +0200
              Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups Don Zickus <dzickus@redhat.com> - 2017-06-27 22:20 +0200
                RE: [PATCH V2] kernel/watchdog: fix spurious hard lockups "Liang, Kan" <kan.liang@intel.com> - 2017-06-27 22:50 +0200
                Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups Don Zickus <dzickus@redhat.com> - 2017-06-27 23:10 +0200
                Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups Andi Kleen <ak@linux.intel.com> - 2017-06-28 01:50 +0200
                Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups Don Zickus <dzickus@redhat.com> - 2017-06-28 21:10 +0200
                Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups Andi Kleen <ak@linux.intel.com> - 2017-06-28 22:20 +0200
                Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups Don Zickus <dzickus@redhat.com> - 2017-06-29 17:50 +0200
                Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups Andi Kleen <ak@linux.intel.com> - 2017-06-29 18:20 +0200
                Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups Don Zickus <dzickus@redhat.com> - 2017-06-29 18:30 +0200
                Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups Andi Kleen <ak@linux.intel.com> - 2017-06-29 18:40 +0200

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