linux-kernel - Re: RCU stalls -> lockup.

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Message-ID: <20141005021556.GC8549@htj.dyndns.org>
Date:	Sat, 4 Oct 2014 22:15:56 -0400
From:	Tejun Heo <tj@...nel.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Dave Jones <davej@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: RCU stalls -> lockup.

On Thu, Oct 02, 2014 at 12:36:55PM -0700, Paul E. McKenney wrote:
> On Thu, Oct 02, 2014 at 01:55:15PM -0400, Dave Jones wrote:
> > I just hit this on my box running 3.17rc7
> > It was followed by a userspace lockup. (Could still ping, and sysrq
> > from the console, but even getty wasn't responding on the console).
> > 
> > I was trying to reproduce another bug faster, and had ramped up the
> > number of processes trinity to uses to 512. This didn't take long
> > to fall out..
> 
> This might be related to an exchange I had with Tejun (CCed), where
> the work queues were running all out, preventing any quiescent states
> from happening.  One fix under consideration is to add a quiescent state,
> similar to the one in softirq handling.

Dave, can you please test whether the following patch makes a
difference if the problem is reproducible?

  http://lkml.kernel.org/r/20141003153701.7c7da030@jlaw-desktop.mno.stratus.com

Thanks.

-- 
tejun
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