Re: 2.6.18-rt1

Dipankar Sarma
2006-09-30T18:18:23Z

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