From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rob Herring Subject: [PATCH v2 06/11] net: calxedaxgmac: fix race with tx queue stop/wake Date: Thu, 29 Aug 2013 22:13:43 -0500 Message-ID: <1377832428-18117-6-git-send-email-robherring2@gmail.com> References: <1377832428-18117-1-git-send-email-robherring2@gmail.com> Cc: Lennert Buytenhek , bhutchings@solarflare.com, Rob Herring To: netdev@vger.kernel.org Return-path: Received: from mail-ob0-f176.google.com ([209.85.214.176]:35858 "EHLO mail-ob0-f176.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753859Ab3H3DOF (ORCPT ); Thu, 29 Aug 2013 23:14:05 -0400 Received: by mail-ob0-f176.google.com with SMTP id uz19so1354239obc.21 for ; Thu, 29 Aug 2013 20:14:05 -0700 (PDT) In-Reply-To: <1377832428-18117-1-git-send-email-robherring2@gmail.com> Sender: netdev-owner@vger.kernel.org List-ID: From: Rob Herring Since the xgmac transmit start and completion work locklessly, it is possible for xgmac_xmit to stop the tx queue after the xgmac_tx_complete has run resulting in the tx queue never being woken up. Fix this by ensuring that ring buffer index updates are visible and recheck the ring space after stopping the queue. The implementation used here was copied from drivers/net/ethernet/broadcom/tg3.c. Signed-off-by: Rob Herring --- v2: - drop netif_tx_lock - use netif_start_queue instead of netif_wake_queue drivers/net/ethernet/calxeda/xgmac.c | 20 +++++++++++++++----- 1 file changed, 15 insertions(+), 5 deletions(-) diff --git a/drivers/net/ethernet/calxeda/xgmac.c b/drivers/net/ethernet/calxeda/xgmac.c index f630855..54be55b 100644 --- a/drivers/net/ethernet/calxeda/xgmac.c +++ b/drivers/net/ethernet/calxeda/xgmac.c @@ -410,6 +410,9 @@ struct xgmac_priv { #define dma_ring_space(h, t, s) CIRC_SPACE(h, t, s) #define dma_ring_cnt(h, t, s) CIRC_CNT(h, t, s) +#define tx_dma_ring_space(p) \ + dma_ring_space((p)->tx_head, (p)->tx_tail, DMA_TX_RING_SZ) + /* XGMAC Descriptor Access Helpers */ static inline void desc_set_buf_len(struct xgmac_dma_desc *p, u32 buf_sz) { @@ -886,8 +889,10 @@ static void xgmac_tx_complete(struct xgmac_priv *priv) priv->tx_tail = dma_ring_incr(entry, DMA_TX_RING_SZ); } - if (dma_ring_space(priv->tx_head, priv->tx_tail, DMA_TX_RING_SZ) > - MAX_SKB_FRAGS) + /* Ensure tx_tail is visible to xgmac_xmit */ + smp_mb(); + if (unlikely(netif_queue_stopped(priv->dev) && + (tx_dma_ring_space(priv) > MAX_SKB_FRAGS))) netif_wake_queue(priv->dev); } @@ -1125,10 +1130,15 @@ static netdev_tx_t xgmac_xmit(struct sk_buff *skb, struct net_device *dev) priv->tx_head = dma_ring_incr(entry, DMA_TX_RING_SZ); - if (dma_ring_space(priv->tx_head, priv->tx_tail, DMA_TX_RING_SZ) < - MAX_SKB_FRAGS) + /* Ensure tx_head update is visible to tx completion */ + smp_mb(); + if (unlikely(tx_dma_ring_space(priv) < MAX_SKB_FRAGS)) { netif_stop_queue(dev); - + /* Ensure netif_stop_queue is visible to tx completion */ + smp_mb(); + if (tx_dma_ring_space(priv) > MAX_SKB_FRAGS) + netif_start_queue(dev); + } return NETDEV_TX_OK; } -- 1.8.1.2