Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755046AbdDLQ4F (ORCPT ); Wed, 12 Apr 2017 12:56:05 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:42356 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752433AbdDLQz7 (ORCPT ); Wed, 12 Apr 2017 12:55:59 -0400 From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, bobby.prani@gmail.com, "Paul E. McKenney" Subject: [PATCH tip/core/rcu 07/13] rcu: Add smp_mb__after_atomic() to sync_exp_work_done() Date: Wed, 12 Apr 2017 09:55:43 -0700 X-Mailer: git-send-email 2.5.2 In-Reply-To: <20170412165441.GA17149@linux.vnet.ibm.com> References: <20170412165441.GA17149@linux.vnet.ibm.com> X-TM-AS-GCONF: 00 x-cbid: 17041216-0048-0000-0000-000001583157 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00006924; HX=3.00000240; KW=3.00000007; PH=3.00000004; SC=3.00000208; SDB=6.00846590; UDB=6.00417599; IPR=6.00625026; BA=6.00005286; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00015022; XFM=3.00000013; UTC=2017-04-12 16:55:56 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17041216-0049-0000-0000-00004071C812 Message-Id: <1492016149-18834-7-git-send-email-paulmck@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-04-12_13:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=1 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1702020001 definitions=main-1704120138 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1235 Lines: 31 The sync_exp_work_done() function needs to fully order the counter-check operation against anything happening after the corresponding grace period. This is a theoretical bug, as all current architectures either provide full ordering for atomic operations on the one hand or implement smp_mb__before_atomic() as smp_mb() on the other. However, a little future-proofing is a good thing, especially given that smp_mb__before_atomic() is only required to provide acquire semantics rather than full ordering. This commit therefore adds smp_mb__after_atomic() after the atomic_long_inc() in sync_exp_work_done(). Reported-by: Dmitry Vyukov Signed-off-by: Paul E. McKenney --- kernel/rcu/tree_exp.h | 1 + 1 file changed, 1 insertion(+) diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h index a7b639ccd46e..e0cafa5f3269 100644 --- a/kernel/rcu/tree_exp.h +++ b/kernel/rcu/tree_exp.h @@ -247,6 +247,7 @@ static bool sync_exp_work_done(struct rcu_state *rsp, atomic_long_t *stat, /* Ensure test happens before caller kfree(). */ smp_mb__before_atomic(); /* ^^^ */ atomic_long_inc(stat); + smp_mb__after_atomic(); /* ^^^ */ return true; } return false; -- 2.5.2