Messages in this thread | | | Subject | Re: [PATCH 06/11] net: calxedaxgmac: fix race with tx queue stop/wake | From | Ben Hutchings <> | Date | Tue, 27 Aug 2013 19:31:57 +0100 |
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On Mon, 2013-08-26 at 17:45 -0500, Rob Herring wrote: > From: Rob Herring <rob.herring@calxeda.com> > > 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 serialize the > queue wake with netif_tx_lock. > > The implementation used here was copied from > drivers/net/ethernet/broadcom/tg3.c. > > Signed-off-by: Rob Herring <rob.herring@calxeda.com> > --- > drivers/net/ethernet/calxeda/xgmac.c | 25 +++++++++++++++++++------ > 1 file changed, 19 insertions(+), 6 deletions(-) > > diff --git a/drivers/net/ethernet/calxeda/xgmac.c b/drivers/net/ethernet/calxeda/xgmac.c > index f630855..cd5872c 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) > { > @@ -886,9 +889,14 @@ 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) > - netif_wake_queue(priv->dev); > + /* Ensure tx_tail is visible to xgmac_xmit */ > + smp_mb(); > + if (unlikely(netif_queue_stopped(priv->dev))) { > + netif_tx_lock(priv->dev); > + if (tx_dma_ring_space(priv) > MAX_SKB_FRAGS) > + netif_wake_queue(priv->dev); > + netif_tx_unlock(priv->dev); > + } > }
You don't need to take the TX lock for this. The memory barriers provide sufficient synchronisation.
> static void xgmac_tx_timeout_work(struct work_struct *work) > @@ -1125,10 +1133,15 @@ 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_wake_queue(dev);
You should use netif_start_queue() rather than netif_wake_queue(), since you know the TX scheduler is already active.
Ben.
> + } > return NETDEV_TX_OK; > } >
-- Ben Hutchings, Staff Engineer, Solarflare Not speaking for my employer; that's the marketing department's job. They asked us to note that Solarflare product names are trademarked.
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