From: Fan Ye <fy15309206903@gmail.com>

tbnet_poll() increments rx_packets once per received frame because that is
the NAPI work unit, and then adds the same number to stats.rx_packets. An
skb is handed to the stack only when the last frame of a packet arrives,
so once the MTU exceeds TBNET_MAX_PAYLOAD_SIZE the statistic reports
frames. tx_packets is bumped once per skb, so the two ends of a link
disagree: at MTU 65330 the receiver reports 16 times the packets its
sender sent.

rx_bytes has the matching problem: frames of a packet that is later
dropped mid-assembly are already accounted, so it does not correspond to
rx_packets as documented. Account for both where the packet is completed,
and leave the NAPI work counter alone.

Fixes: e69b6c02b4c3 ("net: Add support for networking over Thunderbolt cable")
Assisted-by: Claude:claude-opus-5
Signed-off-by: Fan Ye <fy15309206903@gmail.com>
---
Seen at MTU 65330 on an ASM4242 host-to-host link, where a packet is 16
frames. On the receiver rx_bytes/rx_packets came out at 4083.9, i.e.
TBNET_MAX_PAYLOAD_SIZE, and rx_packets ran 15.9x the IP layer's InReceives;
with the patch they are 65308.3 and 0.99. At the default MTU a packet fits
in one frame and the counters already agree, which is why this went
unnoticed.
---
 drivers/net/thunderbolt/main.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/net/thunderbolt/main.c b/drivers/net/thunderbolt/main.c
index 98893732bc6e..43ee896f1b17 100644
--- a/drivers/net/thunderbolt/main.c
+++ b/drivers/net/thunderbolt/main.c
@@ -892,9 +892,11 @@ static int tbnet_poll(struct napi_struct *napi, int budget)
 		       le32_to_cpu(net->rx_hdr.frame_count) - 1;
 
 		rx_packets++;
-		net->stats.rx_bytes += frame_size;
 
 		if (last) {
+			/* Before eth_type_trans() pulls the Ethernet header. */
+			net->stats.rx_packets++;
+			net->stats.rx_bytes += skb->len;
 			skb->protocol = eth_type_trans(skb, net->dev);
 			trace_tbnet_rx_skb(skb);
 			napi_gro_receive(&net->napi, skb);
@@ -902,8 +904,6 @@ static int tbnet_poll(struct napi_struct *napi, int budget)
 		}
 	}
 
-	net->stats.rx_packets += rx_packets;
-
 	if (cleaned_count)
 		tbnet_alloc_rx_buffers(net, cleaned_count);
 

---
base-commit: dac3e89a2c90c2feeb471e1f22a2512ad424b792
change-id: 20260815-tbnet-rx-stats-34a9d0541257

Best regards,
--  
Fan Ye <fy15309206903@gmail.com>

On Sat, Aug 15, 2026 at 10:21:52AM +0000, Fan Ye via B4 Relay wrote:
> From: Fan Ye <fy15309206903@gmail.com>
> 
> tbnet_poll() increments rx_packets once per received frame because that is
> the NAPI work unit, and then adds the same number to stats.rx_packets. An
> skb is handed to the stack only when the last frame of a packet arrives,
> so once the MTU exceeds TBNET_MAX_PAYLOAD_SIZE the statistic reports
> frames. tx_packets is bumped once per skb, so the two ends of a link
> disagree: at MTU 65330 the receiver reports 16 times the packets its
> sender sent.
> 
> rx_bytes has the matching problem: frames of a packet that is later
> dropped mid-assembly are already accounted, so it does not correspond to
> rx_packets as documented. Account for both where the packet is completed,
> and leave the NAPI work counter alone.
> 
> Fixes: e69b6c02b4c3 ("net: Add support for networking over Thunderbolt cable")
> Assisted-by: Claude:claude-opus-5
> Signed-off-by: Fan Ye <fy15309206903@gmail.com>

Acked-by: Mika Westerberg <westeri@kernel.org>

On Sat, Aug 15, 2026 at 10:21:52AM +0000, Fan Ye via B4 Relay wrote:
> From: Fan Ye <fy15309206903@gmail.com>
> 
> tbnet_poll() increments rx_packets once per received frame because that is
> the NAPI work unit, and then adds the same number to stats.rx_packets. An
> skb is handed to the stack only when the last frame of a packet arrives,
> so once the MTU exceeds TBNET_MAX_PAYLOAD_SIZE the statistic reports
> frames. tx_packets is bumped once per skb, so the two ends of a link
> disagree: at MTU 65330 the receiver reports 16 times the packets its
> sender sent.
> 
> rx_bytes has the matching problem: frames of a packet that is later
> dropped mid-assembly are already accounted, so it does not correspond to
> rx_packets as documented. Account for both where the packet is completed,
> and leave the NAPI work counter alone.
> 
> Fixes: e69b6c02b4c3 ("net: Add support for networking over Thunderbolt cable")
> Assisted-by: Claude:claude-opus-5
> Signed-off-by: Fan Ye <fy15309206903@gmail.com>
> ---
> Seen at MTU 65330 on an ASM4242 host-to-host link, where a packet is 16
> frames. On the receiver rx_bytes/rx_packets came out at 4083.9, i.e.
> TBNET_MAX_PAYLOAD_SIZE, and rx_packets ran 15.9x the IP layer's InReceives;
> with the patch they are 65308.3 and 0.99. At the default MTU a packet fits
> in one frame and the counters already agree, which is why this went
> unnoticed.

Reviewed-by: Simon Horman <horms@kernel.org>