linux-kernel - Re: rcu_dyntick and suspicious RCU usage

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Date:	Tue, 17 Jul 2012 13:58:56 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Fengguang Wu <wfg@...ux.intel.com>
Cc:	Josh Triplett <josh@...htriplett.org>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: rcu_dyntick and suspicious RCU usage

On Fri, Jul 13, 2012 at 05:12:30PM +0800, Fengguang Wu wrote:
> On Thu, Jul 12, 2012 at 10:02:42AM -0700, Paul E. McKenney wrote:
> > On Fri, Jul 13, 2012 at 12:57:38AM +0800, Fengguang Wu wrote:
> > > On Thu, Jul 12, 2012 at 09:43:08AM -0700, Paul E. McKenney wrote:
> > > > On Wed, Jul 11, 2012 at 12:49:24AM -0700, Paul E. McKenney wrote:
> > > > > On Tue, Jul 10, 2012 at 12:47:00PM +0800, Fengguang Wu wrote:
> > > > > > Hi Paul,
> > > > > > 
> > > > > > Fortunately this bug is bisectable and the first bad commit is:
> > > > > > 
> > > > > >         commit 9b2e4f1880b789be1f24f9684f7a54b90310b5c0
> > > > > >         Author: Paul E. McKenney <paul.mckenney@...aro.org>
> > > > > >         Date:   Fri Sep 30 12:10:22 2011 -0700
> > > > > > 
> > > > > >             rcu: Track idleness independent of idle tasks
> > > > > 
> > > > > OK, there is a problem in TINY_RCU's handling of dyntick-idle: it
> > > > > traces while in idle.  The confusion on my part was that in TREE_RCU,
> > > > > the nesting and dyntick-idle indication are different, while in
> > > > > TINY_RCU they are one and the same.
> > > > > 
> > > > > Does the following patch help?
> > > > 
> > > > This one failed in my testing.  Please see the end for the fixed
> > > > version, with on small but important change.
> > > 
> > > It worked, thanks!
> > > 
> > > Tested-by: Fengguang Wu <wfg@...ux.intel.com>
> > 
> > Very good!  (And please ignore my resend of the same patch.)
> > 
> > I will queue this.
> 
> Will you recommend it for -stable? It impacts 3.3/3.4. I tested it on
> 3.4 and it works fine. However for 3.3, the patch cannot apply cleanly.

If someone hits it in a real workload, I might consider it.  I currently
have it queued for 3.7.

							Thanx, Paul

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