Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261553AbVCRKDv (ORCPT ); Fri, 18 Mar 2005 05:03:51 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261554AbVCRKDv (ORCPT ); Fri, 18 Mar 2005 05:03:51 -0500 Received: from mx2.elte.hu ([157.181.151.9]:25762 "EHLO mx2.elte.hu") by vger.kernel.org with ESMTP id S261553AbVCRKDt (ORCPT ); Fri, 18 Mar 2005 05:03:49 -0500 Date: Fri, 18 Mar 2005 11:03:39 +0100 From: Ingo Molnar To: "Paul E. McKenney" Cc: dipankar@in.ibm.com, shemminger@osdl.org, akpm@osdl.org, torvalds@osdl.org, rusty@au1.ibm.com, tgall@us.ibm.com, jim.houston@comcast.net, manfred@colorfullife.com, gh@us.ibm.com, linux-kernel@vger.kernel.org Subject: Re: Real-Time Preemption and RCU Message-ID: <20050318100339.GA15386@elte.hu> References: <20050318002026.GA2693@us.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20050318002026.GA2693@us.ibm.com> User-Agent: Mutt/1.4.1i X-ELTE-SpamVersion: MailScanner 4.31.6-itk1 (ELTE 1.2) SpamAssassin 2.63 ClamAV 0.73 X-ELTE-VirusStatus: clean X-ELTE-SpamCheck: no X-ELTE-SpamCheck-Details: score=-4.9, required 5.9, autolearn=not spam, BAYES_00 -4.90 X-ELTE-SpamLevel: X-ELTE-SpamScore: -4 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1361 Lines: 40 there's a problem in #5's rcu_read_lock(): void rcu_read_lock(void) { preempt_disable(); if (current->rcu_read_lock_nesting++ == 0) { current->rcu_read_lock_ptr = &__get_cpu_var(rcu_data).lock; read_lock(current->rcu_read_lock_ptr); } preempt_enable(); } not only are read_lock()-ed sections preemptible, read_lock() itself may block, so it cannot be called from within preempt_disable(). How about something like: void rcu_read_lock(void) { preempt_disable(); if (current->rcu_read_lock_nesting++ == 0) { current->rcu_read_lock_ptr = &__get_cpu_var(rcu_data).lock; preempt_enable(); read_lock(current->rcu_read_lock_ptr); } else preempt_enable(); } this would still make it 'statistically scalable' - but is it correct? Ingo - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/