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=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS 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 8C4C7C31E5B for ; Wed, 19 Jun 2019 01:19:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6B60F2085A for ; Wed, 19 Jun 2019 01:19:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729566AbfFSBTO (ORCPT ); Tue, 18 Jun 2019 21:19:14 -0400 Received: from mx1.redhat.com ([209.132.183.28]:26467 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726037AbfFSBTO (ORCPT ); Tue, 18 Jun 2019 21:19:14 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id D802130832F2; Wed, 19 Jun 2019 01:19:13 +0000 (UTC) Received: from t460p.redhat.com (ovpn-117-83.phx2.redhat.com [10.3.117.83]) by smtp.corp.redhat.com (Postfix) with ESMTP id E9E9B17C41; Wed, 19 Jun 2019 01:19:12 +0000 (UTC) From: Scott Wood To: Sebastian Andrzej Siewior Cc: "Paul E. McKenney" , Peter Zijlstra , Steven Rostedt , Thomas Gleixner , Juri Lelli , Clark Williams , linux-rt-users@vger.kernel.org, linux-kernel@vger.kernel.org, Scott Wood Subject: [PATCH RT 1/4] rcu: Acquire RCU lock when disabling BHs Date: Tue, 18 Jun 2019 20:19:05 -0500 Message-Id: <20190619011908.25026-2-swood@redhat.com> In-Reply-To: <20190619011908.25026-1-swood@redhat.com> References: <20190619011908.25026-1-swood@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.44]); Wed, 19 Jun 2019 01:19:14 +0000 (UTC) Sender: linux-rt-users-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-rt-users@vger.kernel.org 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 __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(); } -- 1.8.3.1