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

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Date:	Thu, 18 Feb 2016 20:13:18 -0800
From:	John Stultz <john.stultz@...aro.org>
To:	Ross Green <rgkernel@...il.com>
Cc:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.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 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?

thanks
-john