via-rhine: close SMP transmit races.

7ab87ff4c770eed71e3777936299292739fcd0fe ("via-rhine: move work from
irq handler to softirq and beyond") forgot to explicitely control the
lifespan of the tx_dirty and tx_cur pointers.

Signed-off-by: Francois Romieu <romieu@fr.zoreil.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/ethernet/via/via-rhine.c b/drivers/net/ethernet/via/via-rhine.c
index 86ca8b2..725106f 100644 (file)
--- a/drivers/net/ethernet/via/via-rhine.c
+++ b/drivers/net/ethernet/via/via-rhine.c
@@ -1779,6 +1779,11 @@ static void rhine_tx_timeout(struct net_device *dev)
        schedule_work(&rp->reset_task);
 }
 
+static inline bool rhine_tx_queue_full(struct rhine_private *rp)
+{
+       return (rp->cur_tx - rp->dirty_tx) >= TX_QUEUE_LEN;
+}
+
 static netdev_tx_t rhine_start_tx(struct sk_buff *skb,
                                  struct net_device *dev)
 {
@@ -1854,6 +1859,12 @@ static netdev_tx_t rhine_start_tx(struct sk_buff *skb,
        wmb();
 
        rp->cur_tx++;
+       /*
+        * Nobody wants cur_tx write to rot for ages after the NIC will have
+        * seen the transmit request, especially as the transmit completion
+        * handler could miss it.
+        */
+       smp_wmb();
 
        /* Non-x86 Todo: explicitly flush cache lines here. */
 
@@ -1866,8 +1877,14 @@ static netdev_tx_t rhine_start_tx(struct sk_buff *skb,
               ioaddr + ChipCmd1);
        IOSYNC;
 
-       if (rp->cur_tx == rp->dirty_tx + TX_QUEUE_LEN)
+       /* dirty_tx may be pessimistically out-of-sync. See rhine_tx. */
+       if (rhine_tx_queue_full(rp)) {
                netif_stop_queue(dev);
+               smp_rmb();
+               /* Rejuvenate. */
+               if (!rhine_tx_queue_full(rp))
+                       netif_wake_queue(dev);
+       }
 
        netif_dbg(rp, tx_queued, dev, "Transmit frame #%d queued in slot %d\n",
                  rp->cur_tx - 1, entry);
@@ -1915,13 +1932,24 @@ static void rhine_tx(struct net_device *dev)
 {
        struct rhine_private *rp = netdev_priv(dev);
        struct device *hwdev = dev->dev.parent;
-       int txstatus = 0, entry = rp->dirty_tx % TX_RING_SIZE;
        unsigned int pkts_compl = 0, bytes_compl = 0;
+       unsigned int dirty_tx = rp->dirty_tx;
+       unsigned int cur_tx;
        struct sk_buff *skb;
 
+       /*
+        * The race with rhine_start_tx does not matter here as long as the
+        * driver enforces a value of cur_tx that was relevant when the
+        * packet was scheduled to the network chipset.
+        * Executive summary: smp_rmb() balances smp_wmb() in rhine_start_tx.
+        */
+       smp_rmb();
+       cur_tx = rp->cur_tx;
        /* find and cleanup dirty tx descriptors */
-       while (rp->dirty_tx != rp->cur_tx) {
-               txstatus = le32_to_cpu(rp->tx_ring[entry].tx_status);
+       while (dirty_tx != cur_tx) {
+               unsigned int entry = dirty_tx % TX_RING_SIZE;
+               u32 txstatus = le32_to_cpu(rp->tx_ring[entry].tx_status);
+
                netif_dbg(rp, tx_done, dev, "Tx scavenge %d status %08x\n",
                          entry, txstatus);
                if (txstatus & DescOwn)
@@ -1970,12 +1998,23 @@ static void rhine_tx(struct net_device *dev)
                pkts_compl++;
                dev_consume_skb_any(skb);
                rp->tx_skbuff[entry] = NULL;
-               entry = (++rp->dirty_tx) % TX_RING_SIZE;
+               dirty_tx++;
        }
 
+       rp->dirty_tx = dirty_tx;
+       /* Pity we can't rely on the nearby BQL completion implicit barrier. */
+       smp_wmb();
+
        netdev_completed_queue(dev, pkts_compl, bytes_compl);
-       if ((rp->cur_tx - rp->dirty_tx) < TX_QUEUE_LEN - 4)
+
+       /* cur_tx may be optimistically out-of-sync. See rhine_start_tx. */
+       if (!rhine_tx_queue_full(rp) && netif_queue_stopped(dev)) {
                netif_wake_queue(dev);
+               smp_rmb();
+               /* Rejuvenate. */
+               if (rhine_tx_queue_full(rp))
+                       netif_stop_queue(dev);
+       }
 }
 
 /**