Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933033AbdIFPaz (ORCPT ); Wed, 6 Sep 2017 11:30:55 -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 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 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Source-IP: userv0022.oracle.com [156.151.31.74] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1684 Lines: 55 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: -- 2.9.3