Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753189Ab3IIMzJ (ORCPT ); Mon, 9 Sep 2013 08:55:09 -0400 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.122]:5811 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751960Ab3IIMzG convert rfc822-to-8bit (ORCPT ); Mon, 9 Sep 2013 08:55:06 -0400 X-Authority-Analysis: v=2.0 cv=fJG7LOme c=1 sm=0 a=Sro2XwOs0tJUSHxCKfOySw==:17 a=Drc5e87SC40A:10 a=JDfofD-L5ZgA:10 a=5SG0PmZfjMsA:10 a=kj9zAlcOel0A:10 a=meVymXHHAAAA:8 a=KGjhK52YXX0A:10 a=5p3hctMY2UsA:10 a=pGLkceISAAAA:8 a=Uf78agF8koMlbh_WU-0A:9 a=CjuIK1q_8ugA:10 a=MSl-tDqOz04A:10 a=Sro2XwOs0tJUSHxCKfOySw==:117 X-Cloudmark-Score: 0 X-Authenticated-User: X-Originating-IP: 67.255.60.225 Date: Mon, 9 Sep 2013 08:55:04 -0400 From: Steven Rostedt To: Frederic Weisbecker Cc: Peter Zijlstra , "Paul E. McKenney" , Eric Dumazet , linux-kernel@vger.kernel.org, mingo@elte.hu, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de, dhowells@redhat.com, edumazet@google.com, darren@dvhart.com, sbw@mit.edu Subject: Re: [PATCH] rcu: Is it safe to enter an RCU read-side critical section? Message-ID: <20130909085504.2ddd7e69@gandalf.local.home> In-Reply-To: <20130909124547.GB16280@somewhere> References: <20130905195234.GA20555@linux.vnet.ibm.com> <20130906105934.GF20519@somewhere> <20130906151851.GQ3966@linux.vnet.ibm.com> <1378488088.31445.39.camel@edumazet-glaptop> <20130906174117.GU3966@linux.vnet.ibm.com> <20130906185927.GE2706@somewhere> <20130909105347.GK31370@twins.programming.kicks-ass.net> <20130909121329.GA16280@somewhere> <20130909083926.3eceebef@gandalf.local.home> <20130909124547.GB16280@somewhere> X-Mailer: Claws Mail 3.9.2 (GTK+ 2.24.20; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1079 Lines: 28 On Mon, 9 Sep 2013 14:45:49 +0200 Frederic Weisbecker wrote: > > This just proves that the caller of rcu_is_cpu_idle() must disable > > preemption itself for the entire time that it needs to use the result > > of rcu_is_cpu_idle(). > > Sorry, I don't understand your point here. What's wrong with checking the > ret from another CPU? Hmm, OK, this is why that code is in desperate need of a comment. >From reading the context a bit more, it seems that the per cpu value is more a "per task" value that happens to be using per cpu variables, and changes on context switches. Is that correct? Anyway, it requires a comment to explain that we are not checking the CPU state, but really the current task state, otherwise that 'ret' value wouldn't travel with the task, but would stick with the CPU. -- Steve -- 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/