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, URIBL_BLOCKED,USER_AGENT_MUTT 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 57DA2C31E4A for ; Thu, 13 Jun 2019 22:37:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3545120673 for ; Thu, 13 Jun 2019 22:37:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726011AbfFMWhY (ORCPT ); Thu, 13 Jun 2019 18:37:24 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:55510 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725798AbfFMWhY (ORCPT ); Thu, 13 Jun 2019 18:37:24 -0400 Received: from pps.filterd (m0098393.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.27/8.16.0.27) with SMTP id x5DMWHoX014019; Thu, 13 Jun 2019 18:36:07 -0400 Received: from pps.reinject (localhost [127.0.0.1]) by mx0a-001b2d01.pphosted.com with ESMTP id 2t3x5ftmbv-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 13 Jun 2019 18:36:07 -0400 Received: from m0098393.ppops.net (m0098393.ppops.net [127.0.0.1]) by pps.reinject (8.16.0.27/8.16.0.27) with SMTP id x5DMWPn8014412; Thu, 13 Jun 2019 18:36:07 -0400 Received: from ppma03dal.us.ibm.com (b.bd.3ea9.ip4.static.sl-reverse.com [169.62.189.11]) by mx0a-001b2d01.pphosted.com with ESMTP id 2t3x5ftmb8-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 13 Jun 2019 18:36:07 -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 x5DMYFFs032479; Thu, 13 Jun 2019 22:36:06 GMT Received: from b01cxnp23033.gho.pok.ibm.com (b01cxnp23033.gho.pok.ibm.com [9.57.198.28]) by ppma03dal.us.ibm.com with ESMTP id 2t1x6frgq4-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 13 Jun 2019 22:36:06 +0000 Received: from b01ledav003.gho.pok.ibm.com (b01ledav003.gho.pok.ibm.com [9.57.199.108]) by b01cxnp23033.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x5DMa5I839321908 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 13 Jun 2019 22:36:05 GMT Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 0D589B206A; Thu, 13 Jun 2019 22:36:05 +0000 (GMT) Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id EC9D5B2067; Thu, 13 Jun 2019 22:36:04 +0000 (GMT) Received: from paulmck-ThinkPad-W541 (unknown [9.85.175.192]) by b01ledav003.gho.pok.ibm.com (Postfix) with ESMTP; Thu, 13 Jun 2019 22:36:04 +0000 (GMT) Received: by paulmck-ThinkPad-W541 (Postfix, from userid 1000) id F17A516C8EAB; Thu, 13 Jun 2019 15:36:04 -0700 (PDT) Date: Thu, 13 Jun 2019 15:36:04 -0700 From: "Paul E. McKenney" To: Peter Zijlstra Cc: rcu@vger.kernel.org, linux-kernel@vger.kernel.org, mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org Subject: Re: [PATCH tip/core/rcu 6/9] rcu: Upgrade sync_exp_work_done() to smp_mb() Message-ID: <20190613223604.GE28207@linux.ibm.com> Reply-To: paulmck@linux.ibm.com References: <20190530145942.GA30318@linux.ibm.com> <20190530150015.30995-6-paulmck@linux.ibm.com> <20190606074849.GD3402@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190606074849.GD3402@hirez.programming.kicks-ass.net> 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=2019-06-13_13:,, 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-1906130170 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 06, 2019 at 09:48:49AM +0200, Peter Zijlstra wrote: > On Thu, May 30, 2019 at 08:00:12AM -0700, Paul E. McKenney wrote: > > The sync_exp_work_done() function uses smp_mb__before_atomic(), but > > there is no obvious atomic in the ensuing code. The ordering is > > absolutely required for grace periods to work correctly, so this > > commit upgrades the smp_mb__before_atomic() to smp_mb(). > > > > Did this commit want a Fixes: line? Such that robots can find the right > kernels to backport this to? Indeed it does, and thanks to Andrea for finding the commit. Thanx, Paul ------------------------------------------------------------------------ commit 96050c68be33edef18800ad6748f61f81db81a20 Author: Paul E. McKenney Date: Sat Apr 20 01:40:54 2019 -0700 rcu: Upgrade sync_exp_work_done() to smp_mb() The sync_exp_work_done() function uses smp_mb__before_atomic(), but there is no obvious atomic in the ensuing code. The ordering is absolutely required for grace periods to work correctly, so this commit upgrades the smp_mb__before_atomic() to smp_mb(). Fixes: 6fba2b3767ea ("rcu: Remove deprecated RCU debugfs tracing code") Reported-by: Andrea Parri Signed-off-by: Paul E. McKenney diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h index 9c990df880d1..d969650a72c6 100644 --- a/kernel/rcu/tree_exp.h +++ b/kernel/rcu/tree_exp.h @@ -259,8 +259,7 @@ static bool sync_exp_work_done(unsigned long s) { if (rcu_exp_gp_seq_done(s)) { trace_rcu_exp_grace_period(rcu_state.name, s, TPS("done")); - /* Ensure test happens before caller kfree(). */ - smp_mb__before_atomic(); /* ^^^ */ + smp_mb(); /* Ensure test happens before caller kfree(). */ return true; } return false;