Subject: Re: RCU callbacks and TREE_PREEMPT_RCU
From: Catalin Marinas <catalin.marinas@arm.com>
To: paulmck@linux.vnet.ibm.com
Cc: Eric Sesterhenn <eric.sesterhenn@lsexperts.de>,
       linux-kernel <linux-kernel@vger.kernel.org>
In-Reply-To: <20090916152929.GA6737@linux.vnet.ibm.com>
References: <1253110641.31751.92.camel@pc1117.cambridge.arm.com>
	 <20090916152929.GA6737@linux.vnet.ibm.com>
Content-Type: text/plain
Organization: ARM Ltd
Date: Wed, 16 Sep 2009 16:34:15 +0100
Message-Id: <1253115255.31751.96.camel@pc1117.cambridge.arm.com>
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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.

-- 
Catalin

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