From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757522AbXISUs5 (ORCPT ); Wed, 19 Sep 2007 16:48:57 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751948AbXISUst (ORCPT ); Wed, 19 Sep 2007 16:48:49 -0400 Received: from e6.ny.us.ibm.com ([32.97.182.146]:45113 "EHLO e6.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750758AbXISUss (ORCPT ); Wed, 19 Sep 2007 16:48:48 -0400 Date: Wed, 19 Sep 2007 13:48:41 -0700 From: "Paul E. McKenney" To: Dmitry Torokhov Cc: Peter Zijlstra , linux-kernel@vger.kernel.org, Ingo Molnar , Andrew Morton , Nick Piggin Subject: Re: [RFC][PATCH 2/6] lockdep: validate rcu_dereference() vs rcu_read_lock() Message-ID: <20070919204841.GH8666@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20070919163111.05c18021@twins> <20070919153750.GB8666@linux.vnet.ibm.com> <20070919173249.GE8666@linux.vnet.ibm.com> <20070919174857.GA11922@linux.vnet.ibm.com> <20070919214110.5d832f28@lappy> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.13 (2006-08-11) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Sep 19, 2007 at 03:49:24PM -0400, Dmitry Torokhov wrote: > On 9/19/07, Peter Zijlstra wrote: > > On Wed, 19 Sep 2007 14:49:56 -0400 "Dmitry Torokhov" > > wrote: > > > > > On 9/19/07, Paul E. McKenney 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. > > Even "slow" driver should try not to slow down the rest of the system > if it can help it. I am sorry if the thing it does do not quite fit in > with the changes you are proposing but it does not make the exeisting > code invalid. > > > If you replace the spin_lock() + sync_sched(), with rcu_read_lock() + > > rcu_call() it should work again without adding an extra lock. > > Except that I need spin_lock_irq for other reasons. I could take the > same lock in write-side code and not use RCU at all but using RCU > allows opening/closing input devices without slowing down interrupt > handlers so why not use it? One approach would be to make rcu_read_held() check for in_interrupt() or some such. This would allow Dmitry's code to stay as it is, for the moment at least. Thanx, Paul