Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965161AbdGTK3n (ORCPT ); Thu, 20 Jul 2017 06:29:43 -0400 Received: from userp1040.oracle.com ([156.151.31.81]:49105 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965140AbdGTK3k (ORCPT ); Thu, 20 Jul 2017 06:29:40 -0400 From: =?UTF-8?q?H=C3=A5kon=20Bugge?= To: Santosh Shilimkar , "David S . Miller" Cc: netdev@vger.kernel.org, linux-rdma@vger.kernel.org, rds-devel@oss.oracle.com, linux-kernel@vger.kernel.org, =?UTF-8?q?H=C3=A5kon=20Bugge?= , =?UTF-8?q?H=C3=A5kon=20Bugge?= Subject: [PATCH net] rds: Make sure updates to cp_send_gen can be observed Date: Thu, 20 Jul 2017 12:28:55 +0200 Message-Id: <20170720102855.21961-1-Haakon.Bugge@oracle.com> X-Mailer: git-send-email 2.9.3 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Source-IP: aserv0022.oracle.com [141.146.126.234] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1560 Lines: 47 cp->cp_send_gen is treated as a normal variable, although it may be used by different threads. This is fixed by using {READ,WRITE}_ONCE when it is incremented and READ_ONCE when it is read outside the {acquire,release}_in_xmit protection. Normative reference from the Linux-Kernel Memory Model: Loads from and stores to shared (but non-atomic) variables should be protected with the READ_ONCE(), WRITE_ONCE(), and ACCESS_ONCE(). Clause 5.1.2.4/25 in the C standard is also relevant. Signed-off-by: Håkon Bugge Reviewed-by: Knut Omang --- net/rds/send.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/net/rds/send.c b/net/rds/send.c index 5cc6403..fa0368c 100644 --- a/net/rds/send.c +++ b/net/rds/send.c @@ -170,8 +170,8 @@ int rds_send_xmit(struct rds_conn_path *cp) * The acquire_in_xmit() check above ensures that only one * caller can increment c_send_gen at any time. */ - cp->cp_send_gen++; - send_gen = cp->cp_send_gen; + send_gen = READ_ONCE(cp->cp_send_gen) + 1; + WRITE_ONCE(cp->cp_send_gen, send_gen); /* * rds_conn_shutdown() sets the conn state and then tests RDS_IN_XMIT, @@ -431,7 +431,7 @@ int rds_send_xmit(struct rds_conn_path *cp) smp_mb(); if ((test_bit(0, &conn->c_map_queued) || !list_empty(&cp->cp_send_queue)) && - send_gen == cp->cp_send_gen) { + send_gen == READ_ONCE(cp->cp_send_gen)) { rds_stats_inc(s_send_lock_queue_raced); if (batch_count < send_batch_count) goto restart; -- 2.9.3