linux-kernel - Re: [BUG] NULL pointer deref with rcutorture

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Date:	Sun, 4 Jan 2009 15:57:26 +0100
From:	Eric Sesterhenn <snakebyte@....de>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, josh@...edesktop.org,
	dipankar@...ibm.com
Subject: Re: [BUG] NULL pointer deref with rcutorture

* Paul E. McKenney (paulmck@...ux.vnet.ibm.com) wrote:
> On Sat, Jan 03, 2009 at 10:40:03AM +0100, Eric Sesterhenn wrote:
> > * Paul E. McKenney (paulmck@...ux.vnet.ibm.com) wrote:
> > > On Sat, Jan 03, 2009 at 12:12:39AM +0100, Eric Sesterhenn wrote:
> > > > * Paul E. McKenney (paulmck@...ux.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
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