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Date: Wed, 19 Sep 2007 21:41:10 +0200
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: "Dmitry Torokhov" <dmitry.torokhov@gmail.com>
Cc: paulmck@linux.vnet.ibm.com, linux-kernel@vger.kernel.org,
       "Ingo Molnar" <mingo@elte.hu>,
       "Andrew Morton" <akpm@linux-foundation.org>,
       "Nick Piggin" <nickpiggin@yahoo.com.au>
Subject: Re: [RFC][PATCH 2/6] lockdep: validate rcu_dereference() vs
 rcu_read_lock()
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On Wed, 19 Sep 2007 14:49:56 -0400 "Dmitry Torokhov"
<dmitry.torokhov@gmail.com> wrote:

> On 9/19/07, Paul E. McKenney <paulmck@linux.vnet.ibm.com> wrote:

> > PS to previous -- any problem with inserting rcu_read_lock() and
> > rcu_read_unlock() around the portion of the IRQ handler that has
> > these accesses?
> >
> 
> I guess I could but it is an extra lock that needs to be managed and
> given the fact that it is not really needed (other to make a newly
> developed tool happy) I am hestsant to do that.

As is, these sites are a bug in -rt and we'll need to fix them anyway.

As for the code you pointed me to, the i8042 driver, it seems to play
way to funny tricks for a simple 'slow' driver.

If you replace the spin_lock() + sync_sched(), with rcu_read_lock() +
rcu_call() it should work again without adding an extra lock.