From patchwork Wed Sep 6 15:29:50 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Haakon Bugge X-Patchwork-Id: 9941015 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id BFF9B6035F for ; Wed, 6 Sep 2017 15:31:17 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id A25DC28C84 for ; Wed, 6 Sep 2017 15:31:17 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 9F36428C8E; Wed, 6 Sep 2017 15:31:17 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.9 required=2.0 tests=BAYES_00, RCVD_IN_DNSWL_HI, UNPARSEABLE_RELAY autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id C029528C9E for ; Wed, 6 Sep 2017 15:31:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932965AbdIFPaw (ORCPT ); Wed, 6 Sep 2017 11:30:52 -0400 Received: from userp1040.oracle.com ([156.151.31.81]:21489 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932770AbdIFPav (ORCPT ); Wed, 6 Sep 2017 11:30:51 -0400 Received: from userv0022.oracle.com (userv0022.oracle.com [156.151.31.74]) by userp1040.oracle.com (Sentrion-MTA-4.3.2/Sentrion-MTA-4.3.2) with ESMTP id v86FUENO027279 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 6 Sep 2017 15:30:14 GMT Received: from userv0121.oracle.com (userv0121.oracle.com [156.151.31.72]) by userv0022.oracle.com (8.14.4/8.14.4) with ESMTP id v86FUDQG021446 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 6 Sep 2017 15:30:13 GMT Received: from abhmp0007.oracle.com (abhmp0007.oracle.com [141.146.116.13]) by userv0121.oracle.com (8.14.4/8.13.8) with ESMTP id v86FUDJi029335; Wed, 6 Sep 2017 15:30:13 GMT Received: from lab02.no.oracle.com (/10.172.144.56) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Wed, 06 Sep 2017 08:30:12 -0700 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, knut.omang@oracle.com Subject: [PATCH net] rds: Fix incorrect statistics counting Date: Wed, 6 Sep 2017 17:29:50 +0200 Message-Id: <20170906152950.17766-1-Haakon.Bugge@oracle.com> X-Mailer: git-send-email 2.9.3 MIME-Version: 1.0 X-Source-IP: userv0022.oracle.com [156.151.31.74] Sender: linux-rdma-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-rdma@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP In rds_send_xmit() there is logic to batch the sends. However, if another thread has acquired the lock, it is considered a race and we yield. The code incrementing the s_send_lock_queue_raced statistics counter did not count this event correctly. This commit removes a small race in determining the race and increments the statistics counter correctly. Signed-off-by: Håkon Bugge Reviewed-by: Knut Omang --- net/rds/send.c | 16 +++++++++++++--- 1 file changed, 13 insertions(+), 3 deletions(-) diff --git a/net/rds/send.c b/net/rds/send.c index 058a407..ecfe0b5 100644 --- a/net/rds/send.c +++ b/net/rds/send.c @@ -101,6 +101,11 @@ void rds_send_path_reset(struct rds_conn_path *cp) } EXPORT_SYMBOL_GPL(rds_send_path_reset); +static bool someone_in_xmit(struct rds_conn_path *cp) +{ + return test_bit(RDS_IN_XMIT, &cp->cp_flags); +} + static int acquire_in_xmit(struct rds_conn_path *cp) { return test_and_set_bit(RDS_IN_XMIT, &cp->cp_flags) == 0; @@ -428,14 +433,19 @@ int rds_send_xmit(struct rds_conn_path *cp) * some work and we will skip our goto */ if (ret == 0) { + bool raced; + smp_mb(); + raced = someone_in_xmit(cp) || + send_gen != READ_ONCE(cp->cp_send_gen); + if ((test_bit(0, &conn->c_map_queued) || - !list_empty(&cp->cp_send_queue)) && - send_gen == READ_ONCE(cp->cp_send_gen)) { - rds_stats_inc(s_send_lock_queue_raced); + !list_empty(&cp->cp_send_queue)) && !raced) { if (batch_count < send_batch_count) goto restart; queue_delayed_work(rds_wq, &cp->cp_send_w, 1); + } else if (raced) { + rds_stats_inc(s_send_lock_queue_raced); } } out: