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

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Message-ID: <20090103015748.GL6842@linux.vnet.ibm.com>
Date:	Fri, 2 Jan 2009 17:57:48 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Eric Sesterhenn <snakebyte@....de>
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

On Sat, Jan 03, 2009 at 12:12:39AM +0100, Eric Sesterhenn wrote:
> * Paul E. McKenney (paulmck@...ux.vnet.ibm.com) wrote:
> > On Sat, Jan 03, 2009 at 12:23:03AM +0530, Kamalesh Babulal wrote:
> > > * Paul E. McKenney <paulmck@...ux.vnet.ibm.com> [2009-01-02 09:58:53]:
> > > 
> > > > On Fri, Jan 02, 2009 at 12:18:19PM +0100, Eric Sesterhenn wrote:
> > > > > Hi,
> > > > > 
> > > > > modprobing rcutorture and removing it again gives me the following oops:
> > > > 
> > > > This looks similar to something that Kamalesh ran into a few weeks ago.
> > > > 
> > > > Kamalesh, did the fixes for that make it to 2.6.28?
> > > > 
> > > > 							Thanx, Paul
> > > > 
> > > 
> > > Hi Paul,
> > > 
> > > 	The fix was available in linux-next from Dec 23 2008 (commit 392ddc32982a5c661dd90dd49a3cb37f1c68b782
> > > 'bio: add support for inlining a number of bio_vecs inside the bio') and it has be pushed for merger in 2.6.29.
> > 
> > Thank you, Kamalesh!
> > 
> > Eric, could you please try applying the above commit and see if the
> > problem reproduces?
> 
> 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?

Looks like someone is (wrongly) freeing some memory that was sent to
call_rcu(), and ftrace might be one way to locate the problem.

							Thanx, Paul
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