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Date: Fri, 20 Mar 2009 12:41:38 -0700
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Ingo Molnar <mingo@elte.hu>
Cc: Steven Rostedt <rostedt@goodmis.org>, LKML <linux-kernel@vger.kernel.org>,
       Thomas Gleixner <tglx@linutronix.de>,
       Peter Zijlstra <peterz@infradead.org>,
       Frederic Weisbecker <fweisbec@gmail.com>
Subject: Re: [PATCH 0/5] [GIT PULL] updates for tip/tracing/ftrace
Message-ID: <20090320194138.GK6698@linux.vnet.ibm.com>
Reply-To: paulmck@linux.vnet.ibm.com
References: <20090318031423.981603258@goodmis.org> <20090318055924.GA24627@elte.hu> <20090318073903.GA31341@elte.hu> <20090319073357.GA14615@elte.hu> <alpine.DEB.2.00.0903191309170.16987@gandalf.stny.rr.com> <20090320174331.GH6698@linux.vnet.ibm.com> <20090320183642.GA2070@elte.hu> <20090320183849.GA3657@elte.hu> <20090320191926.GJ6698@linux.vnet.ibm.com> <20090320192721.GI6224@elte.hu>
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On Fri, Mar 20, 2009 at 08:27:21PM +0100, Ingo Molnar wrote:
> 
> * Paul E. McKenney <paulmck@linux.vnet.ibm.com> wrote:
> 
> > On Fri, Mar 20, 2009 at 07:38:49PM +0100, Ingo Molnar wrote:
> > > 
> > > * Ingo Molnar <mingo@elte.hu> wrote:
> > > 
> > > > > > This looks like it is RCU/stop_machine related. The CPU is 
> > > > > > stuck in in stop_machine? I see that rcu_torture is running. 
> > > > > > Does this go away if you turn off rcu_torture?
> > > > > 
> > > > > Grasping at straws...  Does Lai's rcu_barrier() fix help?
> > > > 
> > > > which one is that?
> > > 
> > > ok, found it. Will know in about ~24 hours whether it helps.
> > 
> > http://lkml.org/lkml/2009/3/20/71 was the one I was thinking of, 
> > just to double-check.
> 
> Yeah - i just picked it up into tip:core/rcu.
> 
> I didnt immediately connect the two things, as 'tracer self-test' 
> does not lend itself to 'CPU hotplug and RCU race fix' - but indeed 
> in the case of the function tracer there's a dependency due to 
> stop_machine_run(). Thanks for point it out!

Thanks go to Steve Rostedt -- I just followed up on his stack-trace
analysis here.  ;-)

						Thanx, Paul