[PATCH net] net: natsemi: fix `rx_dropped` double accounting on `netif_rx()` failure

[PATCH net] net: natsemi: fix `rx_dropped` double accounting on `netif_rx()` failure

[Yeounsu Moon]

`netif_rx()` already increments `rx_dropped` core stat when it fails.
The driver was also updating `ndev->stats.rx_dropped` in the same path.
Since both are reported together via `ip -s -s` command, this resulted
in drops being counted twice in user-visible stats.

Keep the driver update on `skb_put()` failure, but skip it after
`netif_rx()` errors.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Yeounsu Moon <yyyynoom@gmail.com>
---
 drivers/net/ethernet/natsemi/ns83820.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/drivers/net/ethernet/natsemi/ns83820.c b/drivers/net/ethernet/natsemi/ns83820.c
index 56d5464222d9..cdbf82affa7b 100644
--- a/drivers/net/ethernet/natsemi/ns83820.c
+++ b/drivers/net/ethernet/natsemi/ns83820.c
@@ -820,7 +820,7 @@ static void rx_irq(struct net_device *ndev)
 	struct ns83820 *dev = PRIV(ndev);
 	struct rx_info *info = &dev->rx_info;
 	unsigned next_rx;
-	int rx_rc, len;
+	int len;
 	u32 cmdsts;
 	__le32 *desc;
 	unsigned long flags;
@@ -881,8 +881,10 @@ static void rx_irq(struct net_device *ndev)
 		if (likely(CMDSTS_OK & cmdsts)) {
 #endif
 			skb_put(skb, len);
-			if (unlikely(!skb))
+			if (unlikely(!skb)) {
+				ndev->stats.rx_dropped++;
 				goto netdev_mangle_me_harder_failed;
+			}
 			if (cmdsts & CMDSTS_DEST_MULTI)
 				ndev->stats.multicast++;
 			ndev->stats.rx_packets++;
@@ -901,15 +903,12 @@ static void rx_irq(struct net_device *ndev)
 				__vlan_hwaccel_put_tag(skb, htons(ETH_P_IPV6), tag);
 			}
 #endif
-			rx_rc = netif_rx(skb);
-			if (NET_RX_DROP == rx_rc) {
-netdev_mangle_me_harder_failed:
-				ndev->stats.rx_dropped++;
-			}
+			netif_rx(skb);
 		} else {
 			dev_kfree_skb_irq(skb);
 		}
 
+netdev_mangle_me_harder_failed:
 		nr++;
 		next_rx = info->next_rx;
 		desc = info->descs + (DESC_SIZE * next_rx);
-- 
2.51.0

Re: [PATCH net] net: natsemi: fix `rx_dropped` double accounting on `netif_rx()` failure

[Simon Horman]

On Thu, Sep 11, 2025 at 02:33:06PM +0900, Yeounsu Moon wrote:
> `netif_rx()` already increments `rx_dropped` core stat when it fails.
> The driver was also updating `ndev->stats.rx_dropped` in the same path.
> Since both are reported together via `ip -s -s` command, this resulted
> in drops being counted twice in user-visible stats.
> 
> Keep the driver update on `skb_put()` failure, but skip it after
> `netif_rx()` errors.
> 
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Signed-off-by: Yeounsu Moon <yyyynoom@gmail.com>

Thanks for your patch,

Thinking out loud: Adding use of ndev->stats to drivers that don't already
do so is discouraged. But here, an existing use is being fixed. And I agree
it is a fix. So this looks good to me.

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

Re: [PATCH net] net: natsemi: fix `rx_dropped` double accounting on `netif_rx()` failure

[Yeounsu Moon]

On Fri Sep 12, 2025 at 10:21 PM KST, Simon Horman wrote:
>
> Thanks for your patch,
>
Thank you very much for your review, Simon :)

> Thinking out loud: Adding use of ndev->stats to drivers that don't already
> do so is discouraged. But here, an existing use is being fixed. And I agree
> it is a fix. So this looks good to me.
>
> Reviewed-by: Simon Horman <horms@kernel.org>
I also noticed that many drivers are still using `ndev->stats`.
If I work on related changes in the future, I will make sure to use
`struct rtnl_link_stats64` instaed and post patches accordingly.

Re: [PATCH net] net: natsemi: fix `rx_dropped` double accounting on `netif_rx()` failure

[Eric Dumazet]

On Wed, Sep 10, 2025 at 10:35 PM Yeounsu Moon <yyyynoom@gmail.com> wrote:
>
> `netif_rx()` already increments `rx_dropped` core stat when it fails.
> The driver was also updating `ndev->stats.rx_dropped` in the same path.
> Since both are reported together via `ip -s -s` command, this resulted
> in drops being counted twice in user-visible stats.
>
> Keep the driver update on `skb_put()` failure, but skip it after
> `netif_rx()` errors.
>
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")

I do not think this Fixes: is correct.

I think core networking got this accounting in netif_rx() in 2010

commit caf586e5f23c (" net: add a core netdev->rx_dropped counter")


> Signed-off-by: Yeounsu Moon <yyyynoom@gmail.com>
> ---
>  drivers/net/ethernet/natsemi/ns83820.c | 13 ++++++-------
>  1 file changed, 6 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/net/ethernet/natsemi/ns83820.c b/drivers/net/ethernet/natsemi/ns83820.c
> index 56d5464222d9..cdbf82affa7b 100644
> --- a/drivers/net/ethernet/natsemi/ns83820.c
> +++ b/drivers/net/ethernet/natsemi/ns83820.c
> @@ -820,7 +820,7 @@ static void rx_irq(struct net_device *ndev)
>         struct ns83820 *dev = PRIV(ndev);
>         struct rx_info *info = &dev->rx_info;
>         unsigned next_rx;
> -       int rx_rc, len;
> +       int len;
>         u32 cmdsts;
>         __le32 *desc;
>         unsigned long flags;
> @@ -881,8 +881,10 @@ static void rx_irq(struct net_device *ndev)
>                 if (likely(CMDSTS_OK & cmdsts)) {
>  #endif
>                         skb_put(skb, len);
> -                       if (unlikely(!skb))

I doubt this driver is used.

Notice that this test  about skb being NULL or not happens after
skb_put(skb, len)
which would have crashed anyway if skb was NULL.


> +                       if (unlikely(!skb)) {
> +                               ndev->stats.rx_dropped++;
>                                 goto netdev_mangle_me_harder_failed;
> +                       }
>                         if (cmdsts & CMDSTS_DEST_MULTI)
>                                 ndev->stats.multicast++;
>                         ndev->stats.rx_packets++;
> @@ -901,15 +903,12 @@ static void rx_irq(struct net_device *ndev)
>                                 __vlan_hwaccel_put_tag(skb, htons(ETH_P_IPV6), tag);
>                         }
>  #endif
> -                       rx_rc = netif_rx(skb);
> -                       if (NET_RX_DROP == rx_rc) {
> -netdev_mangle_me_harder_failed:
> -                               ndev->stats.rx_dropped++;
> -                       }
> +                       netif_rx(skb);
>                 } else {
>                         dev_kfree_skb_irq(skb);
>                 }
>
> +netdev_mangle_me_harder_failed:
>                 nr++;
>                 next_rx = info->next_rx;
>                 desc = info->descs + (DESC_SIZE * next_rx);
> --
> 2.51.0
>

Re: [PATCH net] net: natsemi: fix `rx_dropped` double accounting on `netif_rx()` failure

[Yeounsu Moon]

On Fri Sep 12, 2025 at 11:19 PM KST, Eric Dumazet wrote:
>
> I do not think this Fixes: is correct.
>
> I think core networking got this accounting in netif_rx() in 2010
>
> commit caf586e5f23c (" net: add a core netdev->rx_dropped counter")
>
I hadn't considered that the Fixes: tag can refer to code outside of the
changes being made. Thank you for pointing this out. I also noticed your
earlier work from 2010.

I'll update the Fixes: tag as you suggested.

>> Signed-off-by: Yeounsu Moon <yyyynoom@gmail.com>
>> ---
>>  drivers/net/ethernet/natsemi/ns83820.c | 13 ++++++-------
>>  1 file changed, 6 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/net/ethernet/natsemi/ns83820.c b/drivers/net/ethernet/natsemi/ns83820.c
>> index 56d5464222d9..cdbf82affa7b 100644
>> --- a/drivers/net/ethernet/natsemi/ns83820.c
>> +++ b/drivers/net/ethernet/natsemi/ns83820.c
>> @@ -820,7 +820,7 @@ static void rx_irq(struct net_device *ndev)
>>         struct ns83820 *dev = PRIV(ndev);
>>         struct rx_info *info = &dev->rx_info;
>>         unsigned next_rx;
>> -       int rx_rc, len;
>> +       int len;
>>         u32 cmdsts;
>>         __le32 *desc;
>>         unsigned long flags;
>> @@ -881,8 +881,10 @@ static void rx_irq(struct net_device *ndev)
>>                 if (likely(CMDSTS_OK & cmdsts)) {
>>  #endif
>>                         skb_put(skb, len);
>> -                       if (unlikely(!skb))
>
> I doubt this driver is used.
>
I also honestly doubt that this driver is still in use.

I came across it while analyzing the `netif_rx()` and `rx_dropped` code
paths, and I noticed that there are quite a few unmanaged drivers using
this kind of code. So I started to fix that.

But If patches like this only burden busy maintainers and reviewers,
I'll stop sending them. That said, I do think leaving unmanaged drivers
as they are is also problematic.

As a newcomer sending patches to netdev, I realized that there are quite
a few such drivers. I don't necessarily believe they all must be actively
maintained, but it feels like some action is needed.


> Notice that this test  about skb being NULL or not happens after
> skb_put(skb, len)
> which would have crashed anyway if skb was NULL.
>
I think I wrote the commit message incorrectly.
The main point was not about `skb_put()`, but rather about the `if`
statement that checks `skb`.
That said, after your comment I realized that `skb_put()` itself also
looks problematic.

Thank you for the detailed review!

	Yeounsu Moon