Re: [BUG] NULL pointer deref with rcutorture

Eric Sesterhenn
2009-01-04T14:57:42Z

* Paul E. McKenney (paulmck@linux.vnet.ibm.com) wrote:
> On Sat, Jan 03, 2009 at 10:40:03AM +0100, Eric Sesterhenn wrote:
> > * Paul E. McKenney (paulmck@linux.vnet.ibm.com) wrote:
> > > On Sat, Jan 03, 2009 at 12:12:39AM +0100, Eric Sesterhenn wrote:
> > > > * Paul E. McKenney (paulmck@linux.vnet.ibm.com) wrote:
> > > >
> > > > I tried to apply the patch from
> > > > http://git.kernel.dk/?p=linux-2.6-block.git;a=commitdiff_plain;h=392ddc32982a5c661dd90dd49a3cb37f1c68b782;hp=bb799ca0202a360fa74d5f17039b9100caebdde7
> > > > but get a message that it is already applied. Seems i already got that
> > > > one.
> > >
> > > Is your configuration able to support ftrace?
> >
> > yes
> >
> > > Looks like someone is (wrongly) freeing some memory that was sent to
> > > call_rcu(), and ftrace might be one way to locate the problem.
> >
> > I set the filter to call_rcu() and call_rcu_sched(), reproduced the
> > oops, and got this in the trace file.
>
> Hmmm... The only unique ones are _rcu_barrier() used during module
> removal by rcutorture and rt_worker_func(), which occurs near the
> beginning of the trace. My next step would be to trace the addresses of
> rcu_head structures passed to call_rcu() and friends and to also trace
> the addresses of the structures as they are invoked (where the original
> NULL-pointer exception occurred).
>
> Is this tracing something you would be interested in taking on? My
> test setup is having some trouble, so it would probably be a couple of
> days before I got it working. :-/

Just tell me what i need to do, I am not really familiar with ftrace.
I am only able to test 2.6.28-04980-gb58602a, since current -git is not
able to boot on this box :|

Greetings, Eric