Re: [PATCH v3 net 2/7] net: enetc: ensure enetc_xdp_xmit() calls enetc_update_tx_ring_tail()

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] net: enetc: missing XDP_XMIT_FLUSH doorbell when k=0
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commit d8271163a46118cc9a3212492775857b3ece7ba0
Author: Vladimir Oltean <vladimir.oltean@nxp.com>

net: enetc: ensure enetc_xdp_xmit() calls enetc_update_tx_ring_tail()

This commit modifies enetc_xdp_xmit() to fix the condition that triggers
the TX doorbell. It removes the redundant xdp_tx_frm_cnt variable and
updates the check to verify if at least one frame was sent along with
flush requests.

> diff --git a/drivers/net/ethernet/freescale/enetc/enetc.c b/drivers/net/ethernet/freescale/enetc/enetc.c
> --- a/drivers/net/ethernet/freescale/enetc/enetc.c
> +++ b/drivers/net/ethernet/freescale/enetc/enetc.c
[ ... ]
> @@ -1845,19 +1844,17 @@ int enetc_xdp_xmit(struct net_device *ndev, int num_frames,
>  						    &xdp_redirect_arr[i]);
>  			break;
>  		}
> -
> -		xdp_tx_frm_cnt++;
>  	}
>  
> -	if (unlikely((flags & XDP_XMIT_FLUSH) || k != xdp_tx_frm_cnt))
> +	if (unlikely(k && ((flags & XDP_XMIT_FLUSH) || k < num_frames)))

[Severity: High]
Does the addition of the k && condition block the mandatory XDP_XMIT_FLUSH
doorbell if the current transmission call fails to enqueue any frames?

If the devmap subsystem enqueues a full batch of frames with flags=0
(no flush), enetc_xdp_xmit() successfully enqueues them but skips the
doorbell because k == num_frames and flags=0.

Subsequently, devmap calls __dev_flush() which invokes enetc_xdp_xmit()
with flags=XDP_XMIT_FLUSH to ring the doorbell. If the hardware TX ring
is now full, this call fails to enqueue its pending frames, resulting in
k=0.

Since the modified condition evaluates to false when k=0, wouldn't this
skip the doorbell entirely and leave the previously enqueued XDP frames
permanently stuck in the hardware TX ring?

>  		enetc_update_tx_ring_tail(tx_ring);
>  
> -	tx_ring->stats.xdp_tx += xdp_tx_frm_cnt;
> -	tx_ring->stats.xdp_tx_drops += num_frames - xdp_tx_frm_cnt;
> +	tx_ring->stats.xdp_tx += k;
> +	tx_ring->stats.xdp_tx_drops += num_frames - k;
>  
>  	enetc_unlock_mdio();
>  
> -	return xdp_tx_frm_cnt;
> +	return k;
>  }
>  EXPORT_SYMBOL_GPL(enetc_xdp_xmit);

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Sashiko AI review · https://sashiko.dev/#/patchset/20260915222735.1016937-1-vladimir.oltean@nxp.com?part=2