Re: rcu_preempt self-detected stall on CPU from 4.5-rc3, since 3.17

[Paul E. McKenney]

On Thu, Feb 18, 2016 at 08:13:18PM -0800, John Stultz wrote:
> On Thu, Feb 18, 2016 at 7:56 PM, Ross Green <rgkernel@xxxxxxxxx> wrote:
> > Well a bonus extra!
> > Kept everything running and there was another stall.
> > So i have included the demsg output for perusal.
> >
> > Just to clear things up there is no hotplug involved in this system.
> > It is a standard Pandaboard ES Ti4460 two processor system.
> > I use this for testing as a generic armv7 processor, plus can keep it
> > just running along for testing for a long time. the system has a total
> > of 23-25 process running on average. Mainly standard daemons. There is
> > certainly no heavy processing going on. I run a series of benchmarks
> > that are cpu intensive for the first 20 miinutes after boot and then
> > just leave it idle away. checking every so often to see how it has
> > gone.
> > As mentioned I have observed these stalls going back to 3.17 kernel.
> > It will often take up to a week to record such a stall. I will
> > typically test every new release kernel, so the -rc? series will get
> > around a weeks testing.
> 
> Sorry. Kind of hopping in a bit late here. Is this always happening
> with just the pandaboard? Or are you seeing this on different
> machines?
> 
> Have you tried enabling CONFIG_DEBUG_TIMEKEEPING just in case
> something is going awry there?

Excellent point -- timekeeping issues have caused this sort of issue
in the past.

Ross, on your next test, could you please enable CONFIG_DEBUG_TIMEKEEPING
as John suggests?

							Thanx, Paul