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

[Jonathan Cameron <Jonathan.Cameron@huawei.com>]

On Wed, 26 Jul 2017 13:28:01 +0100
Jonathan Cameron <Jonathan.Cameron@huawei.com> wrote:

> On Wed, 26 Jul 2017 10:32:32 +0100
> Jonathan Cameron <Jonathan.Cameron@huawei.com> wrote:
> 
> > On Wed, 26 Jul 2017 09:16:23 +0100
> > Jonathan Cameron <Jonathan.Cameron@huawei.com> wrote:
> >   
> > > On Tue, 25 Jul 2017 21:12:17 -0700
> > > "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> wrote:
> > >     
> > > > On Tue, Jul 25, 2017 at 09:02:33PM -0700, David Miller wrote:      
> > > > > From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
> > > > > Date: Tue, 25 Jul 2017 20:55:45 -0700
> > > > >         
> > > > > > On Tue, Jul 25, 2017 at 02:10:29PM -0700, David Miller wrote:        
> > > > > >> Just to report, turning softlockup back on fixes things for me on
> > > > > >> sparc64 too.        
> > > > > > 
> > > > > > Very good!
> > > > > >         
> > > > > >> 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.
> > > > > >         
> > > > > >> 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
> 
> > Jonathan
> >   
> > > 
> > > Jonathan
> > > 
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