linux-kernel - Re: rcu_dyntick and suspicious RCU usage

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Message-ID: <20120712165738.GA21630@localhost>
Date:	Fri, 13 Jul 2012 00:57:38 +0800
From:	Fengguang Wu <wfg@...ux.intel.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.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 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>

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