From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932554AbeAROGu (ORCPT ); Thu, 18 Jan 2018 09:06:50 -0500 Received: from mail-pg0-f65.google.com ([74.125.83.65]:35343 "EHLO mail-pg0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932337AbeAROGp (ORCPT ); Thu, 18 Jan 2018 09:06:45 -0500 X-Google-Smtp-Source: ACJfBouwDC0HiEukR0IeXqADEuNq8thbAhCY4za6lE4joiuF+7B6zI3w/hhGidvyCC9PlR8/bay9gQ== To: nic_swsd@realtek.com, romieu@fr.zoreil.com, alexander.h.duyck@redhat.com, David Miller , dhowells@redhat.com, paulmck@linux.vnet.ibm.com, will.deacon@arm.com, peterz@infradead.org Cc: netdev@vger.kernel.org, Linux Kernel Mailing List From: Jia-Ju Bai Subject: net: r8169: a question of memory barrier in the r8169 driver Message-ID: <9a373156-41e5-a78b-cd31-c4b9bdba2696@gmail.com> Date: Thu, 18 Jan 2018 22:06:17 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.2.0 MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org In the rt8169 driver, the function "rtl_tx" uses "smp_mb" to sync the writing operation with rtl8169_start_xmit: if (tp->dirty_tx != dirty_tx) { tp->dirty_tx = dirty_tx; smp_mb(); ... } The function rtl8169_start_xmit reads tp->dirty_tx in TX_FRAGS_READY_FOR: if (unlikely(!TX_FRAGS_READY_FOR(tp, skb_shinfo(skb)->nr_frags))) { netif_err(tp, drv, dev, "BUG! Tx Ring full when queue awake!\n"); goto err_stop_0; } But there is no memory barrier around this code. Is there a possible data race here? If not, how this data race is avoided? Thanks, Jia-Ju Bai