On Wed, 26 Jul 2017 13:28:01 +0100
Jonathan Cameron [off-list ref] wrote:

On Wed, 26 Jul 2017 10:32:32 +0100
Jonathan Cameron [off-list ref] wrote:

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On Wed, 26 Jul 2017 09:16:23 +0100
Jonathan Cameron [off-list ref] wrote:
  

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On Tue, 25 Jul 2017 21:12:17 -0700
"Paul E. McKenney" [off-list ref] wrote:
    

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On Tue, Jul 25, 2017 at 09:02:33PM -0700, David Miller wrote:      

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From: "Paul E. McKenney" <redacted>
Date: Tue, 25 Jul 2017 20:55:45 -0700
        

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On Tue, Jul 25, 2017 at 02:10:29PM -0700, David Miller wrote:        

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Just to report, turning softlockup back on fixes things for me on
sparc64 too.        

Very good!
        

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The thing about softlockup is it runs an hrtimer, which seems to run
about every 4 seconds.        

I could see where that could shake things loose, but I am surprised that
it would be needed.  I ran a short run with CONFIG_SOFTLOCKUP_DETECTOR=y
with no trouble, but I will be running a longer test later on.
        

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So I wonder if this is a NO_HZ problem.        

Might be.  My tests run with NO_HZ_FULL=n and NO_HZ_IDLE=y.  What are
you running?  (Again, my symptoms are slightly different, so I might
be seeing a different bug.)        

I run with NO_HZ_FULL=n and NO_HZ_IDLE=y, just like you.

To clarify, the symptoms show up with SOFTLOCKUP_DETECTOR disabled.        

Same here -- but my failure case happens fairly rarely, so it will take
some time to gain reasonable confidence that enabling SOFTLOCKUP_DETECTOR
had effect.

But you are right, might be interesting to try NO_HZ_PERIODIC=y
or NO_HZ_FULL=y.  So many possible tests, and so little time.  ;-)

							Thanx, Paul
      

I'll be the headless chicken running around and trying as many tests
as I can fit in.  Typical time to see the failure for us is sub 10
minutes so we'll see how far we get.

Make me a list to run if you like ;)

NO_HZ_PERIODIC=y running now.    

By which I mean CONFIG_HZ_PERIODIC=y

Anyhow, run for 40 minutes with out seeing a splat but my sanity check
on the NO_FULL_HZ=n and NO_HZ_IDLE=y this morning took 20 minutes so
I won't have much confidence until we are a few hours in on this.

Anyhow, certainly looking like a promising direction for investigation!
  

Well it's done over 3 hours without a splat so I think it is fine with
CONFIG_HZ_PERIODIC=y

As I think we expected, the problem occurs with NO_HZ_FULL.
Happened pretty quickly but given the somewhat random nature,
might just be coincidence.

Jonathan

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Jonathan
  

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Jonathan

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