[PATCH net-next 2/2] net: plumb drop reasons to __dev_queue_xmit()

[Eric Dumazet <edumazet@google.com>]

Add drop reasons to __dev_queue_xmit():

- SKB_DROP_REASON_DEV_READY : device is not UP.

- SKB_DROP_REASON_RECURSION_LIMIT : recursion limit on virtual device is hit.

Also add an unlikely() for the SKB_DROP_REASON_DEV_READY case,
and reduce indentation level.

Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 net/core/dev.c | 83 ++++++++++++++++++++++++++------------------------
 1 file changed, 43 insertions(+), 40 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index f48dc299e4b270f2fedba11e669d4940e73f0d4d..200d44883fc130dcc80afa1ddccce68bf3ff592c 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4745,9 +4745,10 @@ int __dev_queue_xmit(struct sk_buff *skb, struct net_device *sb_dev)
 {
 	struct net_device *dev = skb->dev;
 	struct netdev_queue *txq = NULL;
-	struct Qdisc *q;
-	int rc = -ENOMEM;
+	enum skb_drop_reason reason;
+	int cpu, rc = -ENOMEM;
 	bool again = false;
+	struct Qdisc *q;
 
 	skb_reset_mac_header(skb);
 	skb_assert_len(skb);
@@ -4816,59 +4817,61 @@ int __dev_queue_xmit(struct sk_buff *skb, struct net_device *sb_dev)
 	 * Check this and shot the lock. It is not prone from deadlocks.
 	 *Either shot noqueue qdisc, it is even simpler 8)
 	 */
-	if (dev->flags & IFF_UP) {
-		int cpu = smp_processor_id(); /* ok because BHs are off */
+	if (unlikely(!(dev->flags & IFF_UP))) {
+		reason = SKB_DROP_REASON_DEV_READY;
+		goto drop;
+	}
 
-		if (!netif_tx_owned(txq, cpu)) {
-			bool is_list = false;
+	cpu = smp_processor_id(); /* ok because BHs are off */
 
-			if (dev_xmit_recursion())
-				goto recursion_alert;
+	if (likely(!netif_tx_owned(txq, cpu))) {
+		bool is_list = false;
 
-			skb = validate_xmit_skb(skb, dev, &again);
-			if (!skb)
-				goto out;
+		if (dev_xmit_recursion())
+			goto recursion_alert;
 
-			HARD_TX_LOCK(dev, txq, cpu);
+		skb = validate_xmit_skb(skb, dev, &again);
+		if (!skb)
+			goto out;
 
-			if (!netif_xmit_stopped(txq)) {
-				is_list = !!skb->next;
+		HARD_TX_LOCK(dev, txq, cpu);
 
-				dev_xmit_recursion_inc();
-				skb = dev_hard_start_xmit(skb, dev, txq, &rc);
-				dev_xmit_recursion_dec();
+		if (!netif_xmit_stopped(txq)) {
+			is_list = !!skb->next;
 
-				/* GSO segments a single SKB into
-				 * a list of frames. TCP expects error
-				 * to mean none of the data was sent.
-				 */
-				if (is_list)
-					rc = NETDEV_TX_OK;
-			}
-			HARD_TX_UNLOCK(dev, txq);
-			if (!skb) /* xmit completed */
-				goto out;
+			dev_xmit_recursion_inc();
+			skb = dev_hard_start_xmit(skb, dev, txq, &rc);
+			dev_xmit_recursion_dec();
 
-			net_crit_ratelimited("Virtual device %s asks to queue packet!\n",
-					     dev->name);
-			/* NETDEV_TX_BUSY or queue was stopped */
-			if (!is_list)
-				rc = -ENETDOWN;
-		} else {
-			/* Recursion is detected! It is possible,
-			 * unfortunately
+			/* GSO segments a single SKB into a list of frames.
+			 * TCP expects error to mean none of the data was sent.
 			 */
-recursion_alert:
-			net_crit_ratelimited("Dead loop on virtual device %s, fix it urgently!\n",
-					     dev->name);
-			rc = -ENETDOWN;
+			if (is_list)
+				rc = NETDEV_TX_OK;
 		}
+		HARD_TX_UNLOCK(dev, txq);
+		if (!skb) /* xmit completed */
+			goto out;
+
+		net_crit_ratelimited("Virtual device %s asks to queue packet!\n",
+				     dev->name);
+		/* NETDEV_TX_BUSY or queue was stopped */
+		if (!is_list)
+			rc = -ENETDOWN;
+	} else {
+		/* Recursion is detected! It is possible unfortunately. */
+recursion_alert:
+		net_crit_ratelimited("Dead loop on virtual device %s, fix it urgently!\n",
+				     dev->name);
+		rc = -ENETDOWN;
 	}
 
+	reason = SKB_DROP_REASON_RECURSION_LIMIT;
+drop:
 	rcu_read_unlock_bh();
 
 	dev_core_stats_tx_dropped_inc(dev);
-	kfree_skb_list(skb);
+	kfree_skb_list_reason(skb, reason);
 	return rc;
 out:
 	rcu_read_unlock_bh();
-- 
2.53.0.880.g73c4285caa-goog