linux-kernel - [PATCH net-next v2 2/9] tun: correct drop statistics in tun_xdp

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Message-ID: <20251125200041.1565663-3-jon@nutanix.com>
Date: Tue, 25 Nov 2025 13:00:29 -0700
From: Jon Kohler <jon@...anix.com>
To: netdev@...r.kernel.org, Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        Jason Wang <jasowang@...hat.com>, Andrew Lunn <andrew+netdev@...n.ch>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Stanislav Fomichev <sdf@...ichev.me>,
        linux-kernel@...r.kernel.org (open list),
        bpf@...r.kernel.org (open list:XDP (eXpress Data Path):Keyword:(?:\b|_)xdp(?:\b|_))
Cc: Jon Kohler <jon@...anix.com>
Subject: [PATCH net-next v2 2/9] tun: correct drop statistics in tun_xdp_one

Add drop reason to kfree_skb calls in tun_xdp_one and ensure that
all failing paths properly increment drop counter.

Signed-off-by: Jon Kohler <jon@...anix.com>
---
 drivers/net/tun.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index dcce49a26800..68ad46ab04a4 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -2392,8 +2392,10 @@ static int tun_xdp_one(struct tun_struct *tun,
 	bool skb_xdp = false;
 	struct page *page;
 
-	if (unlikely(datasize < ETH_HLEN))
+	if (unlikely(datasize < ETH_HLEN)) {
+		dev_core_stats_rx_dropped_inc(tun->dev);
 		return -EINVAL;
+	}
 
 	xdp_prog = rcu_dereference(tun->xdp_prog);
 	if (xdp_prog) {
@@ -2407,6 +2409,7 @@ static int tun_xdp_one(struct tun_struct *tun,
 		act = bpf_prog_run_xdp(xdp_prog, xdp);
 		ret = tun_xdp_act(tun, xdp_prog, xdp, act);
 		if (ret < 0) {
+			/* tun_xdp_act already handles drop statistics */
 			put_page(virt_to_head_page(xdp->data));
 			return ret;
 		}
@@ -2435,6 +2438,7 @@ static int tun_xdp_one(struct tun_struct *tun,
 build:
 	skb = build_skb(xdp->data_hard_start, buflen);
 	if (!skb) {
+		dev_core_stats_rx_dropped_inc(tun->dev);
 		return -ENOMEM;
 	}
 
@@ -2453,7 +2457,8 @@ static int tun_xdp_one(struct tun_struct *tun,
 	tnl_hdr = (struct virtio_net_hdr_v1_hash_tunnel *)gso;
 	if (tun_vnet_hdr_tnl_to_skb(tun->flags, features, skb, tnl_hdr)) {
 		atomic_long_inc(&tun->rx_frame_errors);
-		kfree_skb(skb);
+		kfree_skb_reason(skb, SKB_DROP_REASON_DEV_HDR);
+		dev_core_stats_rx_dropped_inc(tun->dev);
 		return -EINVAL;
 	}
 
@@ -2479,7 +2484,8 @@ static int tun_xdp_one(struct tun_struct *tun,
 
 		if (unlikely(tfile->detached)) {
 			spin_unlock(&queue->lock);
-			kfree_skb(skb);
+			kfree_skb_reason(skb, SKB_DROP_REASON_DEV_READY);
+			dev_core_stats_rx_dropped_inc(tun->dev);
 			return -EBUSY;
 		}
 
-- 
2.43.0