From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754448AbcKUSYn (ORCPT ); Mon, 21 Nov 2016 13:24:43 -0500 Received: from smtprelay0206.hostedemail.com ([216.40.44.206]:36324 "EHLO smtprelay.hostedemail.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753620AbcKUSYm (ORCPT ); Mon, 21 Nov 2016 13:24:42 -0500 X-Session-Marker: 726F737465647440676F6F646D69732E6F7267 X-Spam-Summary: 2,0,0,,d41d8cd98f00b204,rostedt@goodmis.org,:::::::::::::::,RULES_HIT:41:355:379:541:599:800:960:973:988:989:1260:1277:1311:1313:1314:1345:1359:1437:1515:1516:1518:1534:1541:1593:1594:1711:1730:1747:1777:1792:2393:2553:2559:2562:3138:3139:3140:3141:3142:3353:3865:3866:3867:3868:3870:3871:3872:3874:4250:5007:6261:7875:8660:9038:10004:10400:10450:10455:10848:10967:11026:11232:11658:11914:12114:12438:12663:12740:12760:13069:13148:13230:13311:13357:13439:14096:14097:14181:14659:14721:19904:19999:21080:30012:30054:30090:30091,0,RBL:none,CacheIP:none,Bayesian:0.5,0.5,0.5,Netcheck:none,DomainCache:0,MSF:not bulk,SPF:fn,MSBL:0,DNSBL:none,Custom_rules:0:0:0,LFtime:2,LUA_SUMMARY:none X-HE-Tag: ice77_62e7bdca70257 X-Filterd-Recvd-Size: 2419 Date: Mon, 21 Nov 2016 13:24:38 -0500 From: Steven Rostedt To: "Paul E. McKenney" Cc: Peter Zijlstra , Andi Kleen , Jiri Olsa , linux-kernel@vger.kernel.org, Ingo Molnar , Josh Triplett , Jan Stancek Subject: Re: [BUG] msr-trace.h:42 suspicious rcu_dereference_check() usage! Message-ID: <20161121132438.2440d82f@gandalf.local.home> In-Reply-To: <20161121125501.768ae998@gandalf.local.home> References: <20161121005343.GB1891@krava> <20161121092850.GF3102@twins.programming.kicks-ass.net> <20161121170612.GT26852@two.firstfloor.org> <20161121171853.GK3092@twins.programming.kicks-ass.net> <20161121125501.768ae998@gandalf.local.home> X-Mailer: Claws Mail 3.14.0 (GTK+ 2.24.31; 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 Paul, On Mon, 21 Nov 2016 12:55:01 -0500 Steven Rostedt wrote: > On Mon, 21 Nov 2016 18:18:53 +0100 > Peter Zijlstra wrote: > > > Its not ftrace as such though, its RCU, ftrace simply uses RCU to avoid > > locking, as one does. > > Just to be clear, as ftrace in the kernel mostly represents function > tracing, which doesn't use RCU. This is a tracepoint feature. > > > > > Biggest objection would be that the rcu_irq_enter_irqson() thing does > > POPF and rcu_irq_exit_irqson() does again. So wrapping every tracepoint > > with that is quite a few cycles. > > Agree. Even though this ends up being a whack-a-mole(TM) fix, I'm not > concerned enough to put a heavy weight rcu idle code in for all > tracepoints. > > Although, what about a percpu flag that can be checked in the > tracepoint code to see if it should enable RCU or not? > > Hmm, I wonder if "rcu_is_watching()" is light enough to have in all > tracepoints? Is it possible to make rcu_is_watching() an inlined call to prevent the overhead of doing a function call? This way we could use this in the fast path of the tracepoint. -- Steve