From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: [PATCH] lockdep: annotate rcu_read_{,un}lock() Date: Fri, 17 Aug 2007 09:56:45 +0200 Message-ID: <1187337405.6114.123.camel@twins> References: <20070815.144628.104052147.davem@davemloft.net> <1187274307.6114.92.camel@twins> <20070816160145.GA16957@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Cc: Ingo Molnar , herbert@gondor.apana.org.au, 123.oleg@gmail.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, David Miller , Daniel Walker , josht@linux.vnet.ibm.com To: paulmck@linux.vnet.ibm.com Return-path: Received: from pentafluge.infradead.org ([213.146.154.40]:57237 "EHLO pentafluge.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759151AbXHQH47 (ORCPT ); Fri, 17 Aug 2007 03:56:59 -0400 In-Reply-To: <20070816160145.GA16957@linux.vnet.ibm.com> Sender: netdev-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Thu, 2007-08-16 at 09:01 -0700, Paul E. McKenney wrote: > On Thu, Aug 16, 2007 at 04:25:07PM +0200, Peter Zijlstra wrote: > > > > There seem to be some unbalanced rcu_read_{,un}lock() issues of late, > > how about doing something like this: > > This will break when rcu_read_lock() and rcu_read_unlock() are invoked > from NMI/SMI handlers -- the raw_local_irq_save() in lock_acquire() will > not mask NMIs or SMIs. > > One approach would be to check for being in an NMI/SMI handler, and > to avoid calling lock_acquire() and lock_release() in those cases. It seems: #define nmi_enter() do { lockdep_off(); __irq_enter(); } while (0) #define nmi_exit() do { __irq_exit(); lockdep_on(); } while (0) Should make it all work out just fine. (for NMIs at least, /me fully ignorant of the workings of SMIs) > Another approach would be to use sparse, which has checks for > rcu_read_lock()/rcu_read_unlock() nesting. Yeah, but one more method can never hurt, no? :-)