From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id F226CC742D7 for ; Fri, 12 Jul 2019 23:29:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BCBEB20863 for ; Fri, 12 Jul 2019 23:29:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728109AbfGLX3i (ORCPT ); Fri, 12 Jul 2019 19:29:38 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:33952 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727708AbfGLX3i (ORCPT ); Fri, 12 Jul 2019 19:29:38 -0400 Received: from pps.filterd (m0098414.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.27/8.16.0.27) with SMTP id x6CNQTvq126655; Fri, 12 Jul 2019 19:27:52 -0400 Received: from pps.reinject (localhost [127.0.0.1]) by mx0b-001b2d01.pphosted.com with ESMTP id 2tq1edmrsk-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Fri, 12 Jul 2019 19:27:51 -0400 Received: from m0098414.ppops.net (m0098414.ppops.net [127.0.0.1]) by pps.reinject (8.16.0.27/8.16.0.27) with SMTP id x6CNRp20129119; Fri, 12 Jul 2019 19:27:51 -0400 Received: from ppma01wdc.us.ibm.com (fd.55.37a9.ip4.static.sl-reverse.com [169.55.85.253]) by mx0b-001b2d01.pphosted.com with ESMTP id 2tq1edmrs7-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Fri, 12 Jul 2019 19:27:51 -0400 Received: from pps.filterd (ppma01wdc.us.ibm.com [127.0.0.1]) by ppma01wdc.us.ibm.com (8.16.0.27/8.16.0.27) with SMTP id x6CNOt68016432; Fri, 12 Jul 2019 23:27:50 GMT Received: from b01cxnp22033.gho.pok.ibm.com (b01cxnp22033.gho.pok.ibm.com [9.57.198.23]) by ppma01wdc.us.ibm.com with ESMTP id 2tjk9770y9-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Fri, 12 Jul 2019 23:27:50 +0000 Received: from b01ledav003.gho.pok.ibm.com (b01ledav003.gho.pok.ibm.com [9.57.199.108]) by b01cxnp22033.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x6CNRoPJ46596522 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Fri, 12 Jul 2019 23:27:50 GMT Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id E7DEFB205F; Fri, 12 Jul 2019 23:27:49 +0000 (GMT) Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 91A01B2065; Fri, 12 Jul 2019 23:27:49 +0000 (GMT) Received: from paulmck-ThinkPad-W541 (unknown [9.85.195.235]) by b01ledav003.gho.pok.ibm.com (Postfix) with ESMTP; Fri, 12 Jul 2019 23:27:49 +0000 (GMT) Received: by paulmck-ThinkPad-W541 (Postfix, from userid 1000) id 01C5C16C39C0; Fri, 12 Jul 2019 16:27:49 -0700 (PDT) Date: Fri, 12 Jul 2019 16:27:49 -0700 From: "Paul E. McKenney" To: Joel Fernandes Cc: Peter Zijlstra , linux-kernel@vger.kernel.org, Alexey Kuznetsov , Bjorn Helgaas , Borislav Petkov , c0d1n61at3@gmail.com, "David S. Miller" , edumazet@google.com, Greg Kroah-Hartman , Hideaki YOSHIFUJI , "H. Peter Anvin" , Ingo Molnar , Josh Triplett , keescook@chromium.org, kernel-hardening@lists.openwall.com, Lai Jiangshan , Len Brown , linux-acpi@vger.kernel.org, linux-pci@vger.kernel.org, linux-pm@vger.kernel.org, Mathieu Desnoyers , neilb@suse.com, netdev@vger.kernel.org, oleg@redhat.com, Pavel Machek , "Rafael J. Wysocki" , Rasmus Villemoes , rcu@vger.kernel.org, Steven Rostedt , Tejun Heo , Thomas Gleixner , will@kernel.org, "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" Subject: Re: [PATCH v1 1/6] rcu: Add support for consolidated-RCU reader checking Message-ID: <20190712232749.GY26519@linux.ibm.com> Reply-To: paulmck@linux.ibm.com References: <20190711234401.220336-1-joel@joelfernandes.org> <20190711234401.220336-2-joel@joelfernandes.org> <20190712111125.GT3402@hirez.programming.kicks-ass.net> <20190712151051.GB235410@google.com> <20190712164531.GW26519@linux.ibm.com> <20190712170631.GA111598@google.com> <20190712174630.GX26519@linux.ibm.com> <20190712194040.GA150253@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190712194040.GA150253@google.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-07-12_06:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1907120241 Sender: linux-pci-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On Fri, Jul 12, 2019 at 03:40:40PM -0400, Joel Fernandes wrote: > On Fri, Jul 12, 2019 at 10:46:30AM -0700, Paul E. McKenney wrote: > > On Fri, Jul 12, 2019 at 01:06:31PM -0400, Joel Fernandes wrote: > > > On Fri, Jul 12, 2019 at 09:45:31AM -0700, Paul E. McKenney wrote: > > > > On Fri, Jul 12, 2019 at 11:10:51AM -0400, Joel Fernandes wrote: > > > > > On Fri, Jul 12, 2019 at 01:11:25PM +0200, Peter Zijlstra wrote: > > > > > > On Thu, Jul 11, 2019 at 07:43:56PM -0400, Joel Fernandes (Google) wrote: > > > > > > > +int rcu_read_lock_any_held(void) > > > > > > > +{ > > > > > > > + int lockdep_opinion = 0; > > > > > > > + > > > > > > > + if (!debug_lockdep_rcu_enabled()) > > > > > > > + return 1; > > > > > > > + if (!rcu_is_watching()) > > > > > > > + return 0; > > > > > > > + if (!rcu_lockdep_current_cpu_online()) > > > > > > > + return 0; > > > > > > > + > > > > > > > + /* Preemptible RCU flavor */ > > > > > > > + if (lock_is_held(&rcu_lock_map)) > > > > > > > > > > > > you forgot debug_locks here. > > > > > > > > > > Actually, it turns out debug_locks checking is not even needed. If > > > > > debug_locks == 0, then debug_lockdep_rcu_enabled() returns 0 and we would not > > > > > get to this point. > > > > > > > > > > > > + return 1; > > > > > > > + > > > > > > > + /* BH flavor */ > > > > > > > + if (in_softirq() || irqs_disabled()) > > > > > > > > > > > > I'm not sure I'd put irqs_disabled() under BH, also this entire > > > > > > condition is superfluous, see below. > > > > > > > > > > > > > + return 1; > > > > > > > + > > > > > > > + /* Sched flavor */ > > > > > > > + if (debug_locks) > > > > > > > + lockdep_opinion = lock_is_held(&rcu_sched_lock_map); > > > > > > > + return lockdep_opinion || !preemptible(); > > > > > > > > > > > > that !preemptible() turns into: > > > > > > > > > > > > !(preempt_count()==0 && !irqs_disabled()) > > > > > > > > > > > > which is: > > > > > > > > > > > > preempt_count() != 0 || irqs_disabled() > > > > > > > > > > > > and already includes irqs_disabled() and in_softirq(). > > > > > > > > > > > > > +} > > > > > > > > > > > > So maybe something lke: > > > > > > > > > > > > if (debug_locks && (lock_is_held(&rcu_lock_map) || > > > > > > lock_is_held(&rcu_sched_lock_map))) > > > > > > return true; > > > > > > > > > > Agreed, I will do it this way (without the debug_locks) like: > > > > > > > > > > ---8<----------------------- > > > > > > > > > > diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c > > > > > index ba861d1716d3..339aebc330db 100644 > > > > > --- a/kernel/rcu/update.c > > > > > +++ b/kernel/rcu/update.c > > > > > @@ -296,27 +296,15 @@ EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held); > > > > > > > > > > int rcu_read_lock_any_held(void) > > > > > { > > > > > - int lockdep_opinion = 0; > > > > > - > > > > > if (!debug_lockdep_rcu_enabled()) > > > > > return 1; > > > > > if (!rcu_is_watching()) > > > > > return 0; > > > > > if (!rcu_lockdep_current_cpu_online()) > > > > > return 0; > > > > > - > > > > > - /* Preemptible RCU flavor */ > > > > > - if (lock_is_held(&rcu_lock_map)) > > > > > - return 1; > > > > > - > > > > > - /* BH flavor */ > > > > > - if (in_softirq() || irqs_disabled()) > > > > > - return 1; > > > > > - > > > > > - /* Sched flavor */ > > > > > - if (debug_locks) > > > > > - lockdep_opinion = lock_is_held(&rcu_sched_lock_map); > > > > > - return lockdep_opinion || !preemptible(); > > > > > + if (lock_is_held(&rcu_lock_map) || lock_is_held(&rcu_sched_lock_map)) > > > > > > > > OK, I will bite... Why not also lock_is_held(&rcu_bh_lock_map)? > > > > > > Hmm, I was borrowing the strategy from rcu_read_lock_bh_held() which does not > > > check for a lock held in this map. > > > > > > Honestly, even lock_is_held(&rcu_sched_lock_map) seems unnecessary per-se > > > since !preemptible() will catch that? rcu_read_lock_sched() disables > > > preemption already, so lockdep's opinion of the matter seems redundant there. > > > > Good point! At least as long as the lockdep splats list RCU-bh among > > the locks held, which they did last I checked. > > > > Of course, you could make the same argument for getting rid of > > rcu_sched_lock_map. Does it make sense to have the one without > > the other? > > It probably makes it inconsistent in the least. I will add the check for > the rcu_bh_lock_map in a separate patch, if that's Ok with you - since I also > want to update the rcu_read_lock_bh_held() logic in the same patch. > > That rcu_read_lock_bh_held() could also just return !preemptible as Peter > suggested for the bh case. Although that seems reasonable, please check the call sites. > > > Sorry I already sent out patches again before seeing your comment but I can > > > rework and resend them based on any other suggestions. > > > > Not a problem! > > Thanks. Depending on whether there is any other feedback, I will work on the > bh_ stuff as a separate patch on top of this series, or work it into the next > series revision if I'm reposting. Hopefully that sounds Ok to you. Agreed -- let's separate concerns. And promote bisectability. Thanx, Paul