From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934328Ab3IDCDc (ORCPT ); Tue, 3 Sep 2013 22:03:32 -0400 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.122]:17232 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934185Ab3IDCDb (ORCPT ); Tue, 3 Sep 2013 22:03:31 -0400 X-Authority-Analysis: v=2.0 cv=ddwCLAre c=1 sm=0 a=Sro2XwOs0tJUSHxCKfOySw==:17 a=Drc5e87SC40A:10 a=6vL9NhcTi7YA:10 a=5SG0PmZfjMsA:10 a=kj9zAlcOel0A:10 a=meVymXHHAAAA:8 a=KGjhK52YXX0A:10 a=Lu4-lkDicUYA:10 a=VnNF1IyMAAAA:8 a=pW_8toMRN_u8kHAsrykA:9 a=CjuIK1q_8ugA:10 a=jeBq3FmKZ4MA:10 a=Sro2XwOs0tJUSHxCKfOySw==:117 X-Cloudmark-Score: 0 X-Authenticated-User: X-Originating-IP: 67.255.60.225 Date: Tue, 3 Sep 2013 22:03:25 -0400 From: Steven Rostedt To: Steven Rostedt Cc: paulmck@linux.vnet.ibm.com, linux-kernel@vger.kernel.org, Ingo Molnar , Andrew Morton , Peter Zijlstra , Frederic Weisbecker , Jiri Olsa Subject: Re: [RFC][PATCH 01/18 v2] ftrace: Add hash list to save RCU unsafe functions Message-ID: <20130903220325.273c2c7d@gandalf.local.home> In-Reply-To: <20130903220115.1018d8f4@gandalf.local.home> References: <20130831051117.884125230@goodmis.org> <20130831051700.601365837@goodmis.org> <20130903171516.16290c47@gandalf.local.home> <20130903221808.GH3871@linux.vnet.ibm.com> <20130903195705.3ba3442f@gandalf.local.home> <20130904012404.GI3871@linux.vnet.ibm.com> <20130903220115.1018d8f4@gandalf.local.home> 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: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 3 Sep 2013 22:01:15 -0400 Steven Rostedt wrote: > On Tue, 3 Sep 2013 18:24:04 -0700 > "Paul E. McKenney" wrote: > > > > > static DEFINE_PER_CPU(unsigned long, ftrace_rcu_func); > > > @@ -588,15 +593,14 @@ static void > > > ftrace_unsafe_callback(unsigned long ip, unsigned long parent_ip, > > > struct ftrace_ops *op, struct pt_regs *pt_regs) > > > { > > > - int bit; > > > - > > > + /* Make sure we see disabled or not first */ > > > + smp_rmb(); > > > > smp_mb__before_atomic_inc()? > > > > Ah, but this is before an atomic_read(), and not an atomic_inc(), thus > the normal smp_rmb() is still required. > Here's the changes against this one: diff --git a/kernel/trace/trace_functions.c b/kernel/trace/trace_functions.c index cdcf187..9e6902a 100644 --- a/kernel/trace/trace_functions.c +++ b/kernel/trace/trace_functions.c @@ -569,14 +569,14 @@ void ftrace_unsafe_rcu_checker_disable(void) { atomic_inc(&ftrace_unsafe_rcu_disabled); /* Make sure the update is seen immediately */ - smp_wmb(); + smp_mb__after_atomic_inc(); } void ftrace_unsafe_rcu_checker_enable(void) { atomic_dec(&ftrace_unsafe_rcu_disabled); /* Make sure the update is seen immediately */ - smp_wmb(); + smp_mb__after_atomic_dec(); } static void Which is nice, because the smp_mb() are now in the really slow path. -- Steve