Re: RCU lockup issues when CONFIG_SOFTLOCKUP_DETECTOR=n - any one else seeing this?

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

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

quoted

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

quoted

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.

quoted

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