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

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Message-ID: <20160219173343.GB3522@linux.vnet.ibm.com>
Date:	Fri, 19 Feb 2016 09:33:43 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	John Stultz <john.stultz@...aro.org>
Cc:	Ross Green <rgkernel@...il.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Lai Jiangshan <jiangshanlai@...il.com>, dipankar@...ibm.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	Josh Triplett <josh@...htriplett.org>,
	rostedt <rostedt@...dmis.org>,
	David Howells <dhowells@...hat.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Darren Hart <dvhart@...ux.intel.com>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Oleg Nesterov <oleg@...hat.com>,
	pranith kumar <bobby.prani@...il.com>
Subject: Re: rcu_preempt self-detected stall on CPU from 4.5-rc3, since 3.17

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@...il.com> 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