Re: [PATCH net] net: bgmac: rate limit RX error messages

[Florian Fainelli <florian.fainelli@broadcom.com>]

On 10/18/26 16:16, Rosen Penev wrote:
> When the RX ring is full the RX FIFO overflows. With RX overflow
> continue enabled, the DMA engine then writes one frame with a bogus
> length (always 0x45c2 on a BCM4716), which the driver drops with
> "Found oversized packet at slot %d, DMA issue!".
> 
> Under sustained overload this happens on every NAPI poll. On an Asus
> RT-N16 a 950 Mbit/s UDP stream to the router printed about 1450 such
> lines in 20 seconds. The messages are printed from NAPI context, so
> with a serial console the router spends most of its time printing.
> 
> The frames are already accounted in rx_length_errors and rx_errors.
> Rate limit both RX error messages. With this change the same flood
> printed 60 lines while rx_length_errors counted 14297 dropped frames.
> 
> Fixes: 6a6c708469c9 ("bgmac: add check for oversized packets")
> Signed-off-by: Rosen Penev <rosenp@gmail.com>
> ---
>   drivers/net/ethernet/broadcom/bgmac.c | 10 ++++++----
>   1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/net/ethernet/broadcom/bgmac.c b/drivers/net/ethernet/broadcom/bgmac.c
> index 1835266fdd09..b3a92ae95de3 100644
> --- a/drivers/net/ethernet/broadcom/bgmac.c
> +++ b/drivers/net/ethernet/broadcom/bgmac.c
> @@ -447,16 +447,18 @@ static int bgmac_dma_rx_read(struct bgmac *bgmac, struct bgmac_dma_ring *ring,
>   
>   			/* Check for poison and drop or pass the packet */
>   			if (len == 0xdead && flags == 0xbeef) {
> -				netdev_err(bgmac->net_dev, "Found poisoned packet at slot %d, DMA issue!\n",
> -					   ring->start);
> +				if (net_ratelimit())
> +					netdev_err(bgmac->net_dev, "Found poisoned packet at slot %d, DMA issue!\n",
> +						   ring->start);
>   				put_page(virt_to_head_page(buf));
>   				bgmac->net_dev->stats.rx_errors++;
>   				break;
>   			}
>   
>   			if (len > BGMAC_RX_ALLOC_SIZE) {
> -				netdev_err(bgmac->net_dev, "Found oversized packet at slot %d, DMA issue!\n",
> -					   ring->start);
> +				if (net_ratelimit())
> +					netdev_err(bgmac->net_dev, "Found oversized packet at slot %d, DMA issue!\n",
> +						   ring->start);

No objection, but the issue is that we are going over 
BGMAC_RX_ALLOC_SIZE, and I believe the check should actually be 
BGMAC_RX_MAX_FRAME_SIZE because we have the skb_shared_info at the end 
of the packet, if we start overflowing that, we will call 
skb_over_panic() very soon.
-- 
Florian