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[2620:137:e000::1:20]) by mx.google.com with ESMTP id c17-20020a05640227d100b00462846fc76fsi9223297ede.108.2022.10.31.07.37.23; Mon, 31 Oct 2022 07:37:50 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231634AbiJaOdH (ORCPT + 99 others); Mon, 31 Oct 2022 10:33:07 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49790 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231304AbiJaOc5 (ORCPT ); Mon, 31 Oct 2022 10:32:57 -0400 X-Greylist: delayed 444 seconds by postgrey-1.37 at lindbergh.monkeyblade.net; Mon, 31 Oct 2022 07:32:55 PDT Received: from mail.draketalley.com (mail.draketalley.com [3.213.214.50]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BA153EE2B; Mon, 31 Oct 2022 07:32:55 -0700 (PDT) Received: from pop-os.lan (cpe-74-72-139-32.nyc.res.rr.com [74.72.139.32]) by mail.draketalley.com (Postfix) with ESMTPSA id 5EC0D55DD6; Mon, 31 Oct 2022 14:25:31 +0000 (UTC) From: drake@draketalley.com To: Manish Chopra , GR-Linux-NIC-Dev@marvell.com, Coiby Xu , Greg Kroah-Hartman , netdev@vger.kernel.org, linux-staging@lists.linux.dev Cc: linux-kernel@vger.kernel.org, Drake Talley Subject: [PATCH 3/3] staging: qlge: add comment explaining memory barrier Date: Mon, 31 Oct 2022 10:25:16 -0400 Message-Id: <20221031142516.266704-4-drake@draketalley.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20221031142516.266704-1-drake@draketalley.com> References: <20221031142516.266704-1-drake@draketalley.com> MIME-Version: 1.0 X-Spam-Status: No, score=-1.2 required=5.0 tests=BAYES_00,SPF_HELO_SOFTFAIL, T_SPF_PERMERROR autolearn=no autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1748214292607454360?= X-GMAIL-MSGID: =?utf-8?q?1748214292607454360?= From: Drake Talley codestyle change that fixes the following report from checkpatch: > WARNING: memory barrier without comment > #2101: FILE: drivers/staging/qlge/qlge_main.c:2101: The added comment identifies the next item from the circular buffer (rx_ring->curr_entry) and its handling/unmapping as the two operations that must not be reordered. Based on the kernel documentation for memory barriers in circular buffers (https://www.kernel.org/doc/Documentation/circular-buffers.txt) and the presence of atomic operations in the current context I'm assuming this usage of the memory barrier is akin to what is explained in the linked doc. There are a couple of other uncommented usages of memory barriers in the current file. If this comment is adequate I can add similar comments to the others. Signed-off-by: Drake Talley --- drivers/staging/qlge/qlge_main.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/drivers/staging/qlge/qlge_main.c b/drivers/staging/qlge/qlge_main.c index c8403dbb5bad..f70390bce6d8 100644 --- a/drivers/staging/qlge/qlge_main.c +++ b/drivers/staging/qlge/qlge_main.c @@ -2098,6 +2098,12 @@ static int qlge_clean_outbound_rx_ring(struct rx_ring *rx_ring) rx_ring->cq_id, prod, rx_ring->cnsmr_idx); net_rsp = (struct qlge_ob_mac_iocb_rsp *)rx_ring->curr_entry; + /* + * Ensure that the next item from the ring buffer is loaded + * before being processed. + * Adding rmb() prevents the compiler from reordering the read + * and subsequent handling of the outbound completion pointer. + */ rmb(); switch (net_rsp->opcode) { case OPCODE_OB_MAC_TSO_IOCB: