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 5A9D7C742D2 for ; Fri, 12 Jul 2019 16:46:45 +0000 (UTC) Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.kernel.org (Postfix) with SMTP id B036820850 for ; Fri, 12 Jul 2019 16:46:44 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B036820850 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-16428-kernel-hardening=archiver.kernel.org@lists.openwall.com Received: (qmail 14205 invoked by uid 550); 12 Jul 2019 16:46:37 -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 14135 invoked from network); 12 Jul 2019 16:46:36 -0000 Date: Fri, 12 Jul 2019 09:45:31 -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: <20190712164531.GW26519@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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190712151051.GB235410@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_04:,, 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=1011 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-1907120171 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)? Thanx, Paul > + return 1; > + return !preemptible(); > } > EXPORT_SYMBOL_GPL(rcu_read_lock_any_held); > >