netdev - Re: suspicious RCU usage warnings in 3.3.0

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Message-Id: <20120411.210843.716144028821174908.davem@davemloft.net>
Date:	Wed, 11 Apr 2012 21:08:43 -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

> If I am confused about the simple function call, and if control is really
> passing via an interrupt or exception, then rcu_irq_enter() should be
> called on entry to the interrupt or exception and rcu_irq_exit() should
> be called on exit.

Hmm, it seems the convention changed such that platforms aren't
supposed to invoke do_softirq() from their trap return trap any more.
It's handled completely by irq_exit().

When did that start happening? :-)

Anyways I bet that's the problem, sparc64 invokes do_softirq() in it's
trap return path if softirqs are pending, and that doesn't do any
of the RCU frobbing you mention.

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