linux-kernel - Re: [ANNOUNCE] 3.0.1-rt11

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Message-ID: <20110830031720.GC2218@linux.vnet.ibm.com>
Date:	Mon, 29 Aug 2011 20:17:20 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Frank Rowand <frank.rowand@...sony.com>
Cc:	"Rowand, Frank" <Frank_Rowand@...yusa.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-rt-users <linux-rt-users@...r.kernel.org>,
	Mike Galbraith <efault@....de>
Subject: Re: [ANNOUNCE] 3.0.1-rt11

On Mon, Aug 29, 2011 at 12:57:21PM -0700, Frank Rowand wrote:
> On 08/26/11 16:55, Paul E. McKenney wrote:
> > On Wed, Aug 24, 2011 at 04:58:49PM -0700, Frank Rowand wrote:
> >> On 08/13/11 03:53, Peter Zijlstra wrote:
> >>>
> >>> Whee, I can skip release announcements too!
> >>>
> >>> So no the subject ain't no mistake its not, 3.0.1-rt11 is there for the
> >>> grabs.
> >>>
> >>> Changes include (including the missing -rt10):
> >>>
> >>>   - hrtimer fix that should make RT_GROUP work again
> >>>   - RCU fixes that should make the RCU stalls go away
> >>>   - fixes SMP=n builds after breaking them in -rt9
> >>
> >> I have a consistent (every boot) hang on boot.  With a few
> >> hacks to get console output, I get the
> >>
> >>   rcu_preempt_state detected stalls on CPUs/tasks
> >>
> >> messages in the attached console log.
> 
> < snip >
> 
> > 
> > Hmmm...  The last few that I have seen that looked like this were
> > due to my messing up rcutorture so that the RCU-boost testing kthreads
> > ran CPU-bound at real-time priority.
> > 
> > Is it possible that something similar is happening on your system?
> > 
> >                                                         Thanx, Paul
> 
> I don't think so.  That would require CONFIG_RCU_TORTURE_TEST, correct?
> And that is not set:
> 
> < way big snip >
> 
> >> # CONFIG_RCU_TORTURE_TEST is not set
> >> CONFIG_RCU_CPU_STALL_TIMEOUT=60
> >> CONFIG_RCU_CPU_STALL_VERBOSE=y
> 
> I'm finally getting back to this today, so I'm starting to learn about
> the RCU stall detector, so maybe I can make some more sense of this.

This condition does not require CONFIG_RCU_TORTURE_TEST, rather, my
bug in CONFIG_RCU_TORTURE_TEST was one way to make this happen.  Any
condition that prevents RCU_SOFTIRQ from ever executing can cause these
symptoms.

							Thanx, Paul
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