Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755684AbdDLRqA (ORCPT ); Wed, 12 Apr 2017 13:46:00 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:37098 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754805AbdDLRkg (ORCPT ); Wed, 12 Apr 2017 13:40:36 -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 21/40] rcu: Expedited wakeups need to be fully ordered Date: Wed, 12 Apr 2017 10:40:06 -0700 X-Mailer: git-send-email 2.5.2 In-Reply-To: <20170412174003.GA23207@linux.vnet.ibm.com> References: <20170412174003.GA23207@linux.vnet.ibm.com> X-TM-AS-GCONF: 00 x-cbid: 17041217-0052-0000-0000-000001D43BF8 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00006924; HX=3.00000240; KW=3.00000007; PH=3.00000004; SC=3.00000208; SDB=6.00846603; UDB=6.00417608; IPR=6.00625041; 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=3.00015023; XFM=3.00000013; UTC=2017-04-12 17:40:33 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17041217-0053-0000-0000-00004FE505FD Message-Id: <1492018825-25634-21-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-1704120145 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1337 Lines: 34 Expedited grace periods use workqueue handlers that wake up the requesters, but there is no lock mediating this wakeup. Therefore, memory barriers are required to ensure that the handler's memory references are seen by all to occur before synchronize_*_expedited() returns to its caller. Possibly detected by syzkaller. Reported-by: Dmitry Vyukov Signed-off-by: Paul E. McKenney --- kernel/rcu/tree_exp.h | 2 ++ 1 file changed, 2 insertions(+) diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h index 51ca287828a2..027e123d93c7 100644 --- a/kernel/rcu/tree_exp.h +++ b/kernel/rcu/tree_exp.h @@ -533,6 +533,7 @@ static void rcu_exp_wait_wake(struct rcu_state *rsp, unsigned long s) rnp->exp_seq_rq = s; spin_unlock(&rnp->exp_lock); } + smp_mb(); /* All above changes before wakeup. */ wake_up_all(&rnp->exp_wq[(rsp->expedited_sequence >> 1) & 0x3]); } trace_rcu_exp_grace_period(rsp->name, s, TPS("endwake")); @@ -614,6 +615,7 @@ static void _synchronize_rcu_expedited(struct rcu_state *rsp, wait_event(rnp->exp_wq[(s >> 1) & 0x3], sync_exp_work_done(rsp, &rdp->exp_workdone0, s)); + smp_mb(); /* Workqueue actions happen before return. */ /* Let the next expedited grace period start. */ mutex_unlock(&rsp->exp_mutex); -- 2.5.2