linux-kernel - Re: [PATCH] BUG: using smp_processor_id() in preemptible [00000000] code: caller is __qdisc

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Message-Id: <1218488979.15798.39.camel@lappy.programming.kicks-ass.net>
Date:	Mon, 11 Aug 2008 23:09:38 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	David Miller <davem@...emloft.net>
Cc:	jkacur@...il.com, linux-rt-users@...r.kernel.org,
	linux-kernel@...r.kernel.org, mingo@...e.hu, tglx@...utronix.de,
	rostedt@...dmis.org
Subject: Re: [PATCH] BUG: using smp_processor_id() in preemptible
	[00000000] code: caller is __qdisc_run

On Mon, 2008-08-11 at 14:00 -0700, David Miller wrote:
> From: "John Kacur" <jkacur@...il.com>
> Date: Mon, 11 Aug 2008 15:11:46 +0200
> 
> > __qdisc_run() calls qdisc_restart() which calls
> > handle_dev_cpu_collision(skb, dev, q); and then the problem shows up
> > here:
> > __get_cpu_var(netdev_rx_stat).cpu_collision++;
> > 
> > The solution is to disable interrupts around the above increment. Here
> > is an attached patch to do so. (Thank's to Peter Zijlstra for help in
> > the analysis and dropping the answer in my lap, so if I got it right
> > it is due to his help, but if I messed it up, then I did that part all
> > by myself.)
> 
> __qdisc_run() always runs in software interrupt context,
> so I guess this is some problem with the -rt stuff running
> software interrupts in threads?

Hmm, good point - and those threads should be cpu affine on -rt if I'm
not mistaken. Steven, do you happen to remember details?

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