From patchwork Mon Jan 30 23:16:41 2012 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Francois Romieu X-Patchwork-Id: 138668 X-Patchwork-Delegate: davem@davemloft.net Return-Path: X-Original-To: patchwork-incoming@ozlabs.org Delivered-To: patchwork-incoming@ozlabs.org Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by ozlabs.org (Postfix) with ESMTP id C9D5DB6F71 for ; Tue, 31 Jan 2012 10:28:00 +1100 (EST) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752771Ab2A3X16 (ORCPT ); Mon, 30 Jan 2012 18:27:58 -0500 Received: from violet.fr.zoreil.com ([92.243.8.30]:51237 "EHLO violet.fr.zoreil.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752404Ab2A3X15 (ORCPT ); Mon, 30 Jan 2012 18:27:57 -0500 Received: from violet.fr.zoreil.com (localhost [127.0.0.1]) by violet.fr.zoreil.com (8.13.8/8.13.8) with ESMTP id q0UNGhds005681; Tue, 31 Jan 2012 00:16:44 +0100 Received: (from romieu@localhost) by violet.fr.zoreil.com (8.13.8/8.13.8/Submit) id q0UNGgGq005680; Tue, 31 Jan 2012 00:16:42 +0100 Date: Tue, 31 Jan 2012 00:16:41 +0100 From: Francois Romieu To: netdev@vger.kernel.org Cc: David Miller , Eric Dumazet , =?utf-8?B?TWljaGHFgiBNaXJvc8WCYXc=?= , Hayes Wang Subject: [PATCH] r8169: fix early Tx queue wake-up. Message-ID: <20120130231641.GA5287@electric-eye.fr.zoreil.com> Mime-Version: 1.0 Content-Disposition: inline User-Agent: Mutt/1.4.2.2i X-Organisation: Land of Sunshine Inc. Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org With infinite gratitude to Eric Dumazet for allowing me to identify the error. Signed-off-by: Francois Romieu Cc: Eric Dumazet Cc: Hayes Wang Acked-by: Eric Dumazet --- I'll address Michał's remarks and add unrelated comments after some sleep. drivers/net/ethernet/realtek/r8169.c | 19 +++++++++++++++++++ 1 files changed, 19 insertions(+), 0 deletions(-) diff --git a/drivers/net/ethernet/realtek/r8169.c b/drivers/net/ethernet/realtek/r8169.c index d039d39..f994606 100644 --- a/drivers/net/ethernet/realtek/r8169.c +++ b/drivers/net/ethernet/realtek/r8169.c @@ -5559,7 +5559,18 @@ static netdev_tx_t rtl8169_start_xmit(struct sk_buff *skb, mmiowb(); if (TX_BUFFS_AVAIL(tp) < MAX_SKB_FRAGS) { + /* Avoid wrongly optimistic queue wake-up: rtl_tx thread must + * not miss a ring update when it notices a stopped queue. + */ + smp_wmb(); netif_stop_queue(dev); + /* Sync with rtl_tx: + * - publish queue status and cur_tx ring index (write barrier) + * - refresh dirty_tx ring index (read barrier). + * May the current thread have a pessimistic view of the ring + * status and forget to wake up queue, a racing rtl_tx thread + * can't. + */ smp_mb(); if (TX_BUFFS_AVAIL(tp) >= MAX_SKB_FRAGS) netif_wake_queue(dev); @@ -5659,6 +5670,14 @@ static void rtl_tx(struct net_device *dev, struct rtl8169_private *tp) if (tp->dirty_tx != dirty_tx) { tp->dirty_tx = dirty_tx; + /* + * Sync with rtl8169_start_xmit: + * - publish dirty_tx ring index (write barrier) + * - refresh cur_tx ring index and queue status (read barrier) + * May the current thread miss the stopped queue condition, + * a racing xmit thread can only have a right view of the + * ring status. + */ smp_mb(); if (netif_queue_stopped(dev) && (TX_BUFFS_AVAIL(tp) >= MAX_SKB_FRAGS)) {