netdev - Re: [patch 11/11] netfilter warning fix

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Message-Id: <20070205181810.bbfbf42c.akpm@linux-foundation.org>
Date:	Mon, 5 Feb 2007 18:18:10 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org, kaber@...sh.net,
	Dipankar Sarma <dipankar@...ibm.com>,
	"Paul E. McKenney" <paulmck@...ibm.com>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [patch 11/11] netfilter warning fix

On Mon, 05 Feb 2007 18:10:26 -0800 (PST) David Miller <davem@...emloft.net> wrote:

> From: akpm@...ux-foundation.org
> Date: Mon, 05 Feb 2007 16:31:11 -0800
> 
> > From: Andrew Morton <akpm@...l.org>
> > 
> > "using smp_processor_id() in preemptible code"
> > 
> > Cc: Patrick McHardy <kaber@...sh.net>
> > Cc: "David S. Miller" <davem@...emloft.net>
> > Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
> 
> We NAK'd this because every patch in the lockdep trace should
> have preemption disabled because software interrupts ought
> to be disabled in those code paths.
> 
> Someone needs to track down why this is really happening.

I think the finger was pointed at preemptible rcu, in -mm.  iirc, the net
stats code is assuming that rcu_read_lock() disables preemption as a side-effect,
which rcu-preempt makes no-longer-true.

Not sure what to do there.  Perhaps add a new
rcu_read_lock_with_preempt_disable() thing which will dtrt with either
config.
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