netdev - Re: suspicious RCU usage warnings in 3.3.0

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Message-Id: <20120411.210319.370705937753558953.davem@davemloft.net>
Date:	Wed, 11 Apr 2012 21:03:19 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	paulmck@...ux.vnet.ibm.com
Cc:	shemminger@...tta.com, mroos@...ux.ee,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: suspicious RCU usage warnings in 3.3.0

From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Date: Wed, 11 Apr 2012 17:45:07 -0700

> On Wed, Apr 11, 2012 at 08:18:54PM -0400, David Miller wrote:
>> From: Stephen Hemminger <shemminger@...tta.com>
>> Date: Wed, 11 Apr 2012 17:10:04 -0700
>> 
>> > On Wed, 11 Apr 2012 16:08:37 -0700
>> > "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> wrote:
>> > 
>> >> Hmmm...  What CPU family is this running on?  From the look of the
>> >> stack, it is sneaking out of idle into softirq without telling RCU.
>> >> This would cause RCU to complain bitterly about being invoked from
>> >> the idle loop -- and RCU ignores CPUs in the idle loop.
>> >> 
>> >> 							Thanx, Paul
>> > 
>> > Sun4... Ping David.
>> 
>> So is there anything specific I need to do in the sparc64
>> idle loop?
> 
> Hmmm...  I must confess that I don't immediately see how control
> is passing from cpu_idle() in arch/sparc/kernel/process_64.c to
> __handle_softirq().
> 
> But it looks like a simple function call in the call trace:

It's coming from the trap return code path at the end of hardware
interrupt processing, on the IRQ stack.
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