1 files changed, 86 insertions, 81 deletions

diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 9461e8ae0529..983c32caf713 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -34,9 +34,6 @@
 #include <net/sock.h>
 #include <net/pkt_sched.h>
 
-#define SCHED_TX_DROP -2
-#define SCHED_TX_QUEUE -3
-
 /* Main transmission queue. */
 
 /* Modifications to data participating in scheduling must be protected with
@@ -68,41 +65,24 @@ static inline int qdisc_qlen(struct Qdisc *q)
         return q->q.qlen;
 }
 
-static inline int handle_dev_cpu_collision(struct net_device *dev)
-{
-        if (unlikely(dev->xmit_lock_owner == smp_processor_id())) {
-                if (net_ratelimit())
-                        printk(KERN_WARNING
-                               "Dead loop on netdevice %s, fix it urgently!\n",
-                               dev->name);
-                return SCHED_TX_DROP;
-        }
-        __get_cpu_var(netdev_rx_stat).cpu_collision++;
-        return SCHED_TX_QUEUE;
-}
-
-static inline int
-do_dev_requeue(struct sk_buff *skb, struct net_device *dev, struct Qdisc *q)
+static inline int dev_requeue_skb(struct sk_buff *skb, struct net_device *dev,
+                                  struct Qdisc *q)
 {
-
         if (unlikely(skb->next))
                 dev->gso_skb = skb;
         else
                 q->ops->requeue(skb, q);
-        /* XXX: Could netif_schedule fail? Or is the fact we are
-         * requeueing imply the hardware path is closed
-         * and even if we fail, some interupt will wake us
-         */
+
         netif_schedule(dev);
         return 0;
 }
 
-static inline struct sk_buff *
-try_get_tx_pkt(struct net_device *dev, struct Qdisc *q)
+static inline struct sk_buff *dev_dequeue_skb(struct net_device *dev,
+                                              struct Qdisc *q)
 {
-        struct sk_buff *skb = dev->gso_skb;
+        struct sk_buff *skb;
 
-        if (skb)
+        if ((skb = dev->gso_skb))
                 dev->gso_skb = NULL;
         else
                 skb = q->dequeue(q);
@@ -110,92 +90,117 @@ try_get_tx_pkt(struct net_device *dev, struct Qdisc *q)
         return skb;
 }
 
-static inline int
-tx_islocked(struct sk_buff *skb, struct net_device *dev, struct Qdisc *q)
+static inline int handle_dev_cpu_collision(struct sk_buff *skb,
+                                           struct net_device *dev,
+                                           struct Qdisc *q)
 {
-        int ret = handle_dev_cpu_collision(dev);
+        int ret;
 
-        if (ret == SCHED_TX_DROP) {
+        if (unlikely(dev->xmit_lock_owner == smp_processor_id())) {
+                /*
+                 * Same CPU holding the lock. It may be a transient
+                 * configuration error, when hard_start_xmit() recurses. We
+                 * detect it by checking xmit owner and drop the packet when
+                 * deadloop is detected. Return OK to try the next skb.
+                 */
                 kfree_skb(skb);
-                return qdisc_qlen(q);
+                if (net_ratelimit())
+                        printk(KERN_WARNING "Dead loop on netdevice %s, "
+                               "fix it urgently!\n", dev->name);
+                ret = qdisc_qlen(q);
+        } else {
+                /*
+                 * Another cpu is holding lock, requeue & delay xmits for
+                 * some time.
+                 */
+                __get_cpu_var(netdev_rx_stat).cpu_collision++;
+                ret = dev_requeue_skb(skb, dev, q);
         }
 
-        return do_dev_requeue(skb, dev, q);
+        return ret;
 }
 
-
 /*
-   NOTE: Called under dev->queue_lock with locally disabled BH.
-
-   __LINK_STATE_QDISC_RUNNING guarantees only one CPU
-   can enter this region at a time.
-
-   dev->queue_lock serializes queue accesses for this device
-   AND dev->qdisc pointer itself.
-
-   netif_tx_lock serializes accesses to device driver.
-
-   dev->queue_lock and netif_tx_lock are mutually exclusive,
-   if one is grabbed, another must be free.
-
-   Multiple CPUs may contend for the two locks.
-
-   Note, that this procedure can be called by a watchdog timer
-
-   Returns to the caller:
-   Returns:  0  - queue is empty or throttled.
-            >0  - queue is not empty.
-
-*/
-
+ * NOTE: Called under dev->queue_lock with locally disabled BH.
+ *
+ * __LINK_STATE_QDISC_RUNNING guarantees only one CPU can process this
+ * device at a time. dev->queue_lock serializes queue accesses for
+ * this device AND dev->qdisc pointer itself.
+ *
+ *  netif_tx_lock serializes accesses to device driver.
+ *
+ *  dev->queue_lock and netif_tx_lock are mutually exclusive,
+ *  if one is grabbed, another must be free.
+ *
+ * Note, that this procedure can be called by a watchdog timer
+ *
+ * Returns to the caller:
+ *                              0  - queue is empty or throttled.
+ *                              >0 - queue is not empty.
+ *
+ */
 static inline int qdisc_restart(struct net_device *dev)
 {
         struct Qdisc *q = dev->qdisc;
-        unsigned lockless = (dev->features & NETIF_F_LLTX);
         struct sk_buff *skb;
+        unsigned lockless;
         int ret;
 
-        skb = try_get_tx_pkt(dev, q);
-        if (skb == NULL)
+        /* Dequeue packet */
+        if (unlikely((skb = dev_dequeue_skb(dev, q)) == NULL))
                 return 0;
 
-        /* we have a packet to send */
-        if (!lockless) {
-                if (!netif_tx_trylock(dev))
-                        return tx_islocked(skb, dev, q);
+        /*
+         * When the driver has LLTX set, it does its own locking in
+         * start_xmit. These checks are worth it because even uncongested
+         * locks can be quite expensive. The driver can do a trylock, as
+         * is being done here; in case of lock contention it should return
+         * NETDEV_TX_LOCKED and the packet will be requeued.
+         */
+        lockless = (dev->features & NETIF_F_LLTX);
+
+        if (!lockless && !netif_tx_trylock(dev)) {
+                /* Another CPU grabbed the driver tx lock */
+                return handle_dev_cpu_collision(skb, dev, q);
         }
-        /* all clear .. */
+
+        /* And release queue */
         spin_unlock(&dev->queue_lock);
 
         ret = NETDEV_TX_BUSY;
         if (!netif_queue_stopped(dev))
-                /* churn baby churn .. */
                 ret = dev_hard_start_xmit(skb, dev);
 
         if (!lockless)
                 netif_tx_unlock(dev);
 
         spin_lock(&dev->queue_lock);
-
-        /* we need to refresh q because it may be invalid since
-         * we dropped  dev->queue_lock earlier ...
-         * So dont try to be clever grasshopper
-         */
         q = dev->qdisc;
-        /* most likely result, packet went ok */
-        if (ret == NETDEV_TX_OK)
-                return qdisc_qlen(q);
-        /* only for lockless drivers .. */
-        if (ret == NETDEV_TX_LOCKED && lockless)
-                return tx_islocked(skb, dev, q);
 
-        if (unlikely (ret != NETDEV_TX_BUSY && net_ratelimit()))
-                printk(KERN_WARNING " BUG %s code %d qlen %d\n",dev->name, ret, q->q.qlen);
+        switch (ret) {
+        case NETDEV_TX_OK:
+                /* Driver sent out skb successfully */
+                ret = qdisc_qlen(q);
+                break;
+
+        case NETDEV_TX_LOCKED:
+                /* Driver try lock failed */
+                ret = handle_dev_cpu_collision(skb, dev, q);
+                break;
+
+        default:
+                /* Driver returned NETDEV_TX_BUSY - requeue skb */
+                if (unlikely (ret != NETDEV_TX_BUSY && net_ratelimit()))
+                        printk(KERN_WARNING "BUG %s code %d qlen %d\n",
+                               dev->name, ret, q->q.qlen);
+
+                ret = dev_requeue_skb(skb, dev, q);
+                break;
+        }
 
-        return do_dev_requeue(skb, dev, q);
+        return ret;
 }
 
-
 void __qdisc_run(struct net_device *dev)
 {
         do {