From cbe157b60c8e70d4b4dc937dfdd39525d8f47b46 Mon Sep 17 00:00:00 2001 From: Rob Herring Date: Fri, 30 Aug 2013 16:49:24 -0500 Subject: [PATCH] net: calxedaxgmac: fix race with tx queue stop/wake 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. Also fix an off-by-one bug where we need to stop the queue when the ring buffer space is equal to MAX_SKB_FRAGS. The implementation used here was copied from drivers/net/ethernet/broadcom/tg3.c. Signed-off-by: Rob Herring Reviewed-by: Ben Hutchings Signed-off-by: David S. Miller --- 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 f63085571241..5d0b61a5c72b 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; } -- GitLab