From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754297AbcKUOWV (ORCPT ); Mon, 21 Nov 2016 09:22:21 -0500 Received: from smtprelay0065.hostedemail.com ([216.40.44.65]:55598 "EHLO smtprelay.hostedemail.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753169AbcKUOWU (ORCPT ); Mon, 21 Nov 2016 09:22:20 -0500 X-Session-Marker: 726F737465647440676F6F646D69732E6F7267 X-Spam-Summary: 2,0,0,,d41d8cd98f00b204,rostedt@goodmis.org,:::::::::::::::::,RULES_HIT:41:355:379:541:599:800:960:973:988:989:1260:1277:1311:1313:1314:1345:1359:1437:1515:1516:1518:1534:1541:1593:1594:1711:1730:1747:1777:1792:2393:2553:2559:2562:3138:3139:3140:3141:3142:3352:3622:3865:3866:3871:3872:3874:4250:5007:6261:7875:10004:10400:10848:10967:11026:11232:11473:11658:11914:12043:12114:12438:12555:12740:12760:13069:13311:13357:13439:14096:14097:14180:14181:14659:14721:21060:21080:21324:30054:30090:30091,0,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: value79_12e1a2247a55 X-Filterd-Recvd-Size: 2400 Date: Mon, 21 Nov 2016 09:20:02 -0500 From: Steven Rostedt To: Peter Zijlstra Cc: Jiri Olsa , "Paul E. McKenney" , linux-kernel@vger.kernel.org, Ingo Molnar , Josh Triplett , Andi Kleen , Jan Stancek , Borislav Petkov Subject: Re: [BUG] msr-trace.h:42 suspicious rcu_dereference_check() usage! Message-ID: <20161121092002.6c4b5315@gandalf.local.home> In-Reply-To: <20161121125830.GE3092@twins.programming.kicks-ass.net> References: <20161121005343.GB1891@krava> <20161121092850.GF3102@twins.programming.kicks-ass.net> <20161121093424.GA9814@krava> <20161121125830.GE3092@twins.programming.kicks-ass.net> 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 On Mon, 21 Nov 2016 13:58:30 +0100 Peter Zijlstra wrote: > On Mon, Nov 21, 2016 at 10:34:25AM +0100, Jiri Olsa wrote: > > > > diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c > > > index 0888a879120f..d6c6aa80675f 100644 > > > --- a/arch/x86/kernel/process.c > > > +++ b/arch/x86/kernel/process.c > > > @@ -357,7 +357,7 @@ static void amd_e400_idle(void) > > > if (!amd_e400_c1e_detected) { > > > u32 lo, hi; > > > > > > - rdmsr(MSR_K8_INT_PENDING_MSG, lo, hi); > > > + RCU_NONIDLE(rdmsr(MSR_K8_INT_PENDING_MSG, lo, hi)); > > > > > > if (lo & K8_INTP_C1E_ACTIVE_MASK) { > > > amd_e400_c1e_detected = true; > > OK, so while looking at this again, I don't like this ether :/ > > Problem with this one is that it always adds the RCU fiddling overhead, > even when we're not tracing. > > I could do an rdmsr_notrace() for this one, dunno if its important. But that would neglect the point of tracing rdmsr. What about: /* tracepoints require RCU enabled */ if (trace_read_msr_enabled()) RCU_NONIDLE(rdmsr(MSR_K8_INT_PENDING_MSG, lo, hi)); else rdmsr(MSR_K8_INT_PENDING_MSG, lo, hi); -- Steve