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Date: Sat, 30 Sep 2006 23:48:04 +0530
From: Dipankar Sarma <dipankar@in.ibm.com>
To: Lee Revell <rlrevell@joe-job.com>
Cc: Ingo Molnar <mingo@elte.hu>, linux-kernel@vger.kernel.org,
       Thomas Gleixner <tglx@linutronix.de>, John Stultz <johnstul@us.ibm.com>,
       "Paul E. McKenney" <paulmck@us.ibm.com>,
       Arjan van de Ven <arjan@infradead.org>
Subject: Re: 2.6.18-rt1
Message-ID: <20060930181804.GA28768@in.ibm.com>
Reply-To: dipankar@in.ibm.com
References: <20060920141907.GA30765@elte.hu> <1159639564.4067.43.camel@mindpipe>
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On Sat, Sep 30, 2006 at 02:06:04PM -0400, Lee Revell wrote:
> On Wed, 2006-09-20 at 16:19 +0200, Ingo Molnar wrote:
> > I'm pleased to announce the 2.6.18-rt1 tree, which can be downloaded 
> > from the usual place:
> > 
> >    http://redhat.com/~mingo/realtime-preempt/
> 
> I got this Oops with -rt3, looks RCU related.  Apologies in advance if
> it's already known.
> 
> Unable to handle kernel NULL pointer dereference at 0000000000000000 RIP: 
>  [<ffffffff802aafa7>] __rcu_read_unlock+0x2e/0x82
> PGD 46a3067 PUD 4e27067 PMD 0 
> Oops: 0002 [1] PREEMPT SMP 
> CPU 1 

I see a very similar crash while running rcutorture on 2.6.18-mm1 and
my rcu patchset that has rcupreempt stuff rom -rt. I don't see this
while running on 2.6.18-rc3, but then rc3 had an older version
of rcutorture. I am working on narrowing it down.

The following script reproduces the problem quickly (within
a couple of minutes) in my 4-cpu x86_64 system -

#! /bin/sh
for ((i=0 ; i<200 ; i++))
do
        echo "Starting pass $i"
        modprobe rcutorture stat_interval=10 # test_no_idle_hz=1 shuffle_interval=5
        sleep 30
        rmmod rcutorture
        dmesg | sed -n -e '/^rcutorture: --- End of test:/p' | tail -1
done
exit 0

Thanks
Dipankar
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