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=ham 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 7EF7EC742D2 for ; Fri, 12 Jul 2019 23:29:02 +0000 (UTC) Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.kernel.org (Postfix) with SMTP id A684E217D4 for ; Fri, 12 Jul 2019 23:29:01 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A684E217D4 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.ibm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kernel-hardening-return-16443-kernel-hardening=archiver.kernel.org@lists.openwall.com Received: (qmail 32058 invoked by uid 550); 12 Jul 2019 23:28:53 -0000 Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Received: (qmail 32005 invoked from network); 12 Jul 2019 23:28:52 -0000 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> 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 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