From 045f977dd4ebdd3ad8e96cf684917adfc5805adb Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Thu, 12 Mar 2026 20:18:24 +0000 Subject: [PATCH] net: plumb drop reasons to __dev_queue_xmit() 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 Reviewed-by: Joe Damato Link: https://patch.msgid.link/20260312201824.203093-3-edumazet@google.com Signed-off-by: Jakub Kicinski --- net/core/dev.c | 103 +++++++++++++++++++++++++------------------------ 1 file changed, 53 insertions(+), 50 deletions(-) diff --git a/net/core/dev.c b/net/core/dev.c index f48dc299e4b2..200d44883fc1 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 (!netif_tx_owned(txq, cpu)) { - bool is_list = false; - - if (dev_xmit_recursion()) - goto recursion_alert; - - skb = validate_xmit_skb(skb, dev, &again); - if (!skb) - goto out; - - HARD_TX_LOCK(dev, txq, cpu); - - if (!netif_xmit_stopped(txq)) { - is_list = !!skb->next; - - dev_xmit_recursion_inc(); - skb = dev_hard_start_xmit(skb, dev, txq, &rc); - dev_xmit_recursion_dec(); - - /* 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; - - 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; - } + if (unlikely(!(dev->flags & IFF_UP))) { + reason = SKB_DROP_REASON_DEV_READY; + goto drop; } + cpu = smp_processor_id(); /* ok because BHs are off */ + + if (likely(!netif_tx_owned(txq, cpu))) { + bool is_list = false; + + if (dev_xmit_recursion()) + goto recursion_alert; + + skb = validate_xmit_skb(skb, dev, &again); + if (!skb) + goto out; + + HARD_TX_LOCK(dev, txq, cpu); + + if (!netif_xmit_stopped(txq)) { + is_list = !!skb->next; + + dev_xmit_recursion_inc(); + skb = dev_hard_start_xmit(skb, dev, txq, &rc); + dev_xmit_recursion_dec(); + + /* 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; + + 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();