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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_MUTT 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 3CB60C43613 for ; Thu, 20 Jun 2019 20:54:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 203872082C for ; Thu, 20 Jun 2019 20:54:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727276AbfFTUyw (ORCPT ); Thu, 20 Jun 2019 16:54:52 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:15468 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726045AbfFTUys (ORCPT ); Thu, 20 Jun 2019 16:54:48 -0400 Received: from pps.filterd (m0098419.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.27/8.16.0.27) with SMTP id x5KKqi34049853; Thu, 20 Jun 2019 16:53:52 -0400 Received: from ppma03dal.us.ibm.com (b.bd.3ea9.ip4.static.sl-reverse.com [169.62.189.11]) by mx0b-001b2d01.pphosted.com with ESMTP id 2t8fwbuvtn-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 20 Jun 2019 16:53:52 -0400 Received: from pps.filterd (ppma03dal.us.ibm.com [127.0.0.1]) by ppma03dal.us.ibm.com (8.16.0.27/8.16.0.27) with SMTP id x5KKoRjB012616; Thu, 20 Jun 2019 20:53:51 GMT Received: from b01cxnp22034.gho.pok.ibm.com (b01cxnp22034.gho.pok.ibm.com [9.57.198.24]) by ppma03dal.us.ibm.com with ESMTP id 2t4ra6c0bv-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 20 Jun 2019 20:53:51 +0000 Received: from b01ledav003.gho.pok.ibm.com (b01ledav003.gho.pok.ibm.com [9.57.199.108]) by b01cxnp22034.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x5KKroaS25035082 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 20 Jun 2019 20:53:50 GMT Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id A024FB205F; Thu, 20 Jun 2019 20:53:50 +0000 (GMT) Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 735C4B2064; Thu, 20 Jun 2019 20:53:50 +0000 (GMT) Received: from paulmck-ThinkPad-W541 (unknown [9.70.82.26]) by b01ledav003.gho.pok.ibm.com (Postfix) with ESMTP; Thu, 20 Jun 2019 20:53:50 +0000 (GMT) Received: by paulmck-ThinkPad-W541 (Postfix, from userid 1000) id 6A6D716C5DE8; Thu, 20 Jun 2019 13:53:52 -0700 (PDT) Date: Thu, 20 Jun 2019 13:53:52 -0700 From: "Paul E. McKenney" To: Scott Wood Cc: Sebastian Andrzej Siewior , Peter Zijlstra , Steven Rostedt , Thomas Gleixner , Juri Lelli , Clark Williams , linux-rt-users@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH RT 1/4] rcu: Acquire RCU lock when disabling BHs Message-ID: <20190620205352.GV26519@linux.ibm.com> Reply-To: paulmck@linux.ibm.com References: <20190619011908.25026-1-swood@redhat.com> <20190619011908.25026-2-swood@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190619011908.25026-2-swood@redhat.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=2019-06-20_14:,, 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-1906200150 Sender: linux-rt-users-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-rt-users@vger.kernel.org On Tue, Jun 18, 2019 at 08:19:05PM -0500, Scott Wood wrote: > A plain local_bh_disable() is documented as creating an RCU critical > section, and (at least) rcutorture expects this to be the case. However, > in_softirq() doesn't block a grace period on PREEMPT_RT, since RCU checks > preempt_count() directly. Even if RCU were changed to check > in_softirq(), that wouldn't allow blocked BH disablers to be boosted. > > Fix this by calling rcu_read_lock() from local_bh_disable(), and update > rcu_read_lock_bh_held() accordingly. > > Signed-off-by: Scott Wood > --- > include/linux/rcupdate.h | 4 ++++ > kernel/rcu/update.c | 4 ++++ > kernel/softirq.c | 12 +++++++++--- > 3 files changed, 17 insertions(+), 3 deletions(-) > > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h > index fb267bc04fdf..aca4e5e25ace 100644 > --- a/include/linux/rcupdate.h > +++ b/include/linux/rcupdate.h > @@ -637,10 +637,12 @@ static inline void rcu_read_unlock(void) > static inline void rcu_read_lock_bh(void) > { > local_bh_disable(); > +#ifndef CONFIG_PREEMPT_RT_FULL How about this instead? if (IS_ENABLED(CONFIG_PREEMPT_RT_FULL)) return; And similarly below. > __acquire(RCU_BH); > rcu_lock_acquire(&rcu_bh_lock_map); > RCU_LOCKDEP_WARN(!rcu_is_watching(), > "rcu_read_lock_bh() used illegally while idle"); > +#endif > } > > /* > @@ -650,10 +652,12 @@ static inline void rcu_read_lock_bh(void) > */ > static inline void rcu_read_unlock_bh(void) > { > +#ifndef CONFIG_PREEMPT_RT_FULL > RCU_LOCKDEP_WARN(!rcu_is_watching(), > "rcu_read_unlock_bh() used illegally while idle"); > rcu_lock_release(&rcu_bh_lock_map); > __release(RCU_BH); > +#endif > local_bh_enable(); > } > > diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c > index 3700b730ea55..eb653a329e0b 100644 > --- a/kernel/rcu/update.c > +++ b/kernel/rcu/update.c > @@ -307,7 +307,11 @@ int rcu_read_lock_bh_held(void) > return 0; > if (!rcu_lockdep_current_cpu_online()) > return 0; > +#ifdef CONFIG_PREEMPT_RT_FULL > + return lock_is_held(&rcu_lock_map) || irqs_disabled(); > +#else > return in_softirq() || irqs_disabled(); > +#endif > } > EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held); > > diff --git a/kernel/softirq.c b/kernel/softirq.c > index 473369122ddd..eb46dd3ff92d 100644 > --- a/kernel/softirq.c > +++ b/kernel/softirq.c > @@ -121,8 +121,10 @@ void __local_bh_disable_ip(unsigned long ip, unsigned int cnt) > long soft_cnt; > > WARN_ON_ONCE(in_irq()); > - if (!in_atomic()) > + if (!in_atomic()) { > local_lock(bh_lock); > + rcu_read_lock(); > + } > soft_cnt = this_cpu_inc_return(softirq_counter); > WARN_ON_ONCE(soft_cnt == 0); > > @@ -155,8 +157,10 @@ void _local_bh_enable(void) > local_irq_restore(flags); > #endif > > - if (!in_atomic()) > + if (!in_atomic()) { > + rcu_read_unlock(); > local_unlock(bh_lock); > + } > } > > void _local_bh_enable_rt(void) > @@ -189,8 +193,10 @@ void __local_bh_enable_ip(unsigned long ip, unsigned int cnt) > WARN_ON_ONCE(count < 0); > local_irq_enable(); > > - if (!in_atomic()) > + if (!in_atomic()) { > + rcu_read_unlock(); > local_unlock(bh_lock); > + } > > preempt_check_resched(); > } And I have to ask... What did you do to test this change to kernel/softirq.c? My past attempts to do this sort of thing have always run afoul of open-coded BH transitions. Thanx, Paul