linux-kernel - Re: RCU callbacks and TREE_PREEMPT

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Message-ID: <20090916154716.GC6737@linux.vnet.ibm.com>
Date:	Wed, 16 Sep 2009 08:47:16 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Catalin Marinas <catalin.marinas@....com>
Cc:	Eric Sesterhenn <eric.sesterhenn@...xperts.de>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: RCU callbacks and TREE_PREEMPT_RCU

On Wed, Sep 16, 2009 at 04:34:15PM +0100, Catalin Marinas wrote:
> On Wed, 2009-09-16 at 08:29 -0700, Paul E. McKenney wrote:
> > On Wed, Sep 16, 2009 at 03:17:21PM +0100, Catalin Marinas wrote:
> > > When TREE_PREEMPT_RCU is enabled, the rcu list traversing above fails
> > > with access to 0x6b6b6b6b but it is fine with TREE_PREEMPT_RCU=n and
> > > TREE_RCU=y. During clean-up, kmemleak objects should no longer be freed
> > > by other means since kmemleak was disabled and all callbacks are
> > > ignored. The system is a 900Mhz P3, 256MB RAM, CONFIG_SMP=n.
> > > 
> > > Is there something I'm doing wrong in kmemleak or a bug with RCU
> > > preemption? The kernel oops looks like this:
> > 
> > From your description and the code above, I must suspect a bug with
> > RCU preemption.  A new one, as the only bugs I am currently chasing
> > involve NR_CPUS>32 (>64 on 64-bit systems).
> > 
> > CONFIG_SMP=n implies NR_CPUS==1 in your build, correct?
> 
> CONFIG_NR_CPUS=1.

I was afraid of that.  ;-)

							Thanx, Paul
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