Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S938293AbdDSQrE (ORCPT ); Wed, 19 Apr 2017 12:47:04 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:49666 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S938191AbdDSQqu (ORCPT ); Wed, 19 Apr 2017 12:46:50 -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, "Michael S. Tsirkin" , "Paul E. McKenney" Subject: [PATCH v3 tip/core/rcu 06/11] hlist_add_tail_rcu disable sparse warning Date: Wed, 19 Apr 2017 09:46:32 -0700 X-Mailer: git-send-email 2.5.2 In-Reply-To: <20170419164553.GA10874@linux.vnet.ibm.com> References: <20170419164553.GA10874@linux.vnet.ibm.com> X-TM-AS-GCONF: 00 x-cbid: 17041916-0044-0000-0000-0000030C74B0 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00006939; HX=3.00000240; KW=3.00000007; PH=3.00000004; SC=3.00000208; SDB=6.00849679; UDB=6.00419581; IPR=6.00628312; BA=6.00005304; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00015095; XFM=3.00000013; UTC=2017-04-19 16:46:42 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17041916-0045-0000-0000-0000073A7AC2 Message-Id: <1492620397-12313-6-git-send-email-paulmck@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-04-19_14:,, 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=8.0.1-1703280000 definitions=main-1704190139 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1440 Lines: 45 From: "Michael S. Tsirkin" sparse is unhappy about this code in hlist_add_tail_rcu: struct hlist_node *i, *last = NULL; for (i = hlist_first_rcu(h); i; i = hlist_next_rcu(i)) last = i; This is because hlist_next_rcu and hlist_next_rcu return __rcu pointers. It's a false positive - it's a write side primitive and so does not need to be called in a read side critical section. The following trivial patch disables the warning without changing the behaviour in any way. Note: __hlist_for_each_rcu would also remove the warning but it would be confusing since it calls rcu_derefence and is designed to run in the rcu read side critical section. Signed-off-by: Michael S. Tsirkin Reviewed-by: Steven Rostedt (VMware) Signed-off-by: Paul E. McKenney --- include/linux/rculist.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/include/linux/rculist.h b/include/linux/rculist.h index 4f7a9561b8c4..b1fd8bf85fdc 100644 --- a/include/linux/rculist.h +++ b/include/linux/rculist.h @@ -509,7 +509,8 @@ static inline void hlist_add_tail_rcu(struct hlist_node *n, { struct hlist_node *i, *last = NULL; - for (i = hlist_first_rcu(h); i; i = hlist_next_rcu(i)) + /* Note: write side code, so rcu accessors are not needed. */ + for (i = h->first; i; i = i->next) last = i; if (last) { -- 2.5.2