From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756031AbdGXVx2 (ORCPT ); Mon, 24 Jul 2017 17:53:28 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:55991 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753666AbdGXVwD (ORCPT ); Mon, 24 Jul 2017 17:52:03 -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, "Paul E. McKenney" Subject: [PATCH tip/core/rcu 12/12] rcu: Move callback-list warning to irq-disable region Date: Mon, 24 Jul 2017 14:51:56 -0700 X-Mailer: git-send-email 2.5.2 In-Reply-To: <20170724215139.GA10881@linux.vnet.ibm.com> References: <20170724215139.GA10881@linux.vnet.ibm.com> X-TM-AS-GCONF: 00 x-cbid: 17072421-0044-0000-0000-00000372BA18 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00007419; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000214; SDB=6.00892374; UDB=6.00446023; IPR=6.00672539; BA=6.00005489; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00016356; XFM=3.00000015; UTC=2017-07-24 21:52:00 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17072421-0045-0000-0000-000007A0C465 Message-Id: <1500933116-11642-12-git-send-email-paulmck@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-07-24_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=8.0.1-1706020000 definitions=main-1707240334 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org After adopting callbacks from a newly offlined CPU, the adopting CPU checks to make sure that its callback list's count is zero only if the list has no callbacks and vice versa. Unfortunately, it does so after enabling interrupts, which means that false positives are possible due to interrupt handlers invoking call_rcu(). Although these false positives are improbable, rcutorture did make it happen once. This commit therefore moves this check to an irq-disabled region of code, thus suppressing the false positive. Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index d330c17c8df4..4b03bddbca3c 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -3869,14 +3869,14 @@ static void rcu_migrate_callbacks(int cpu, struct rcu_state *rsp) rcu_advance_cbs(rsp, rnp_root, rdp); /* Leverage recent GPs. */ rcu_advance_cbs(rsp, rnp_root, my_rdp); /* Assign GP to pending CBs. */ rcu_segcblist_merge(&my_rdp->cblist, &rdp->cblist); + WARN_ON_ONCE(rcu_segcblist_empty(&my_rdp->cblist) != + !rcu_segcblist_n_cbs(&my_rdp->cblist)); raw_spin_unlock_irqrestore_rcu_node(rnp_root, flags); WARN_ONCE(rcu_segcblist_n_cbs(&rdp->cblist) != 0 || !rcu_segcblist_empty(&rdp->cblist), "rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, 1stCB=%p\n", cpu, rcu_segcblist_n_cbs(&rdp->cblist), rcu_segcblist_first_cb(&rdp->cblist)); - WARN_ON_ONCE(rcu_segcblist_empty(&my_rdp->cblist) != - !rcu_segcblist_n_cbs(&my_rdp->cblist)); } /* -- 2.5.2