[PATCH net-next] udp: add drop count for packets in udp_prod_queue

[Mahdi Faramarzpour <mahdifrmx@gmail.com>]

This commit adds SNMP drop count increment for the packets in
per NUMA queues which were introduced in commit b650bf0977d3
("udp: remove busylock and add per NUMA queues"). note that SNMP
counters are incremented currently by the caller for skb. And
that these skbs on the intermediate queue cannot be counted
there so need similar logic in their error path.

Signed-off-by: Mahdi Faramarzpour <mahdifrmx@gmail.com>
---
v7:
  - revert the last change and fix style
v6: https://lore.kernel.org/netdev/20260128070311.48892-1-mahdifrmx@gmail.com/
  - increasing a single counter based on socket family
v5: https://lore.kernel.org/netdev/20260122185357.50922-1-mahdifrmx@gmail.com/
  - check if drop counts are non-zero before increasing countrers
v4: https://lore.kernel.org/netdev/20260108102950.49417-1-mahdifrmx@gmail.com/
  - move all changes to unlikely(to_drop) branch
v3: https://lore.kernel.org/netdev/20260105114732.140719-1-mahdifrmx@gmail.com/
  - remove the unreachable UDP_MIB_RCVBUFERRORS code
v2: https://lore.kernel.org/netdev/20260105071218.10785-1-mahdifrmx@gmail.com/
  - change ENOMEM to ENOBUFS
v1: https://lore.kernel.org/netdev/20260104105732.427691-1-mahdifrmx@gmail.com/
---
 net/ipv4/udp.c | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index ffe074cb5..6ad7296db 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1793,14 +1793,32 @@ int __udp_enqueue_schedule_skb(struct sock *sk, struct sk_buff *skb)
 	}
 
 	if (unlikely(to_drop)) {
+		int err_ipv4 = 0;
+		int err_ipv6 = 0;
+
 		for (nb = 0; to_drop != NULL; nb++) {
 			skb = to_drop;
+			if (skb->protocol == htons(ETH_P_IP))
+				err_ipv4++;
+			else
+				err_ipv6++;
 			to_drop = skb->next;
 			skb_mark_not_on_list(skb);
-			/* TODO: update SNMP values. */
 			sk_skb_reason_drop(sk, skb, SKB_DROP_REASON_PROTO_MEM);
 		}
 		numa_drop_add(&udp_sk(sk)->drop_counters, nb);
+		if (err_ipv4 > 0) {
+			SNMP_ADD_STATS(__UDPX_MIB(sk, true), UDP_MIB_MEMERRORS,
+				       err_ipv4);
+			SNMP_ADD_STATS(__UDPX_MIB(sk, true), UDP_MIB_INERRORS,
+				       err_ipv4);
+		}
+		if (err_ipv6 > 0) {
+			SNMP_ADD_STATS(__UDPX_MIB(sk, false), UDP_MIB_MEMERRORS,
+				       err_ipv6);
+			SNMP_ADD_STATS(__UDPX_MIB(sk, false), UDP_MIB_INERRORS,
+				       err_ipv6);
+		}
 	}
 
 	atomic_sub(total_size, &udp_prod_queue->rmem_alloc);
-- 
2.34.1