linux-kernel - Re: [PATCH net-next v2] net: mana: Handle SKB if TX SGEs exceed hardware limit

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Message-ID: <20251031162611.2a981fdf@kernel.org>
Date: Fri, 31 Oct 2025 16:26:11 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Aditya Garg <gargaditya@...ux.microsoft.com>
Cc: kys@...rosoft.com, haiyangz@...rosoft.com, wei.liu@...nel.org,
 decui@...rosoft.com, andrew+netdev@...n.ch, davem@...emloft.net,
 edumazet@...gle.com, pabeni@...hat.com, longli@...rosoft.com,
 kotaranov@...rosoft.com, horms@...nel.org,
 shradhagupta@...ux.microsoft.com, ssengar@...ux.microsoft.com,
 ernis@...ux.microsoft.com, dipayanroy@...ux.microsoft.com,
 shirazsaleem@...rosoft.com, linux-hyperv@...r.kernel.org,
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-rdma@...r.kernel.org, gargaditya@...rosoft.com
Subject: Re: [PATCH net-next v2] net: mana: Handle SKB if TX SGEs exceed
 hardware limit

On Wed, 29 Oct 2025 06:12:35 -0700 Aditya Garg wrote:
> @@ -289,6 +290,21 @@ netdev_tx_t mana_start_xmit(struct sk_buff *skb, struct net_device *ndev)
>  	cq = &apc->tx_qp[txq_idx].tx_cq;
>  	tx_stats = &txq->stats;
>  
> +	if (MAX_SKB_FRAGS + 2 > MAX_TX_WQE_SGL_ENTRIES &&
> +	    skb_shinfo(skb)->nr_frags + 2 > MAX_TX_WQE_SGL_ENTRIES) {
> +		/* GSO skb with Hardware SGE limit exceeded is not expected here
> +		 * as they are handled in mana_features_check() callback
> +		 */
> +		if (skb_is_gso(skb))
> +			netdev_warn_once(ndev, "GSO enabled skb exceeds max SGE limit\n");

This could be the same question Simon asked but why do you think you
need this line? Sure you need to linearize non-GSO but why do you care
to warn specifically about GSO?! Looks like defensive programming or
testing leftover..

> +		if (skb_linearize(skb)) {
> +			netdev_warn_once(ndev, "Failed to linearize skb with nr_frags=%d and is_gso=%d\n",
> +					 skb_shinfo(skb)->nr_frags,
> +					 skb_is_gso(skb));

.. in practice including is_gso() here as you do is probably enough for
debug

> +			goto tx_drop_count;
> +		}
> +	}
> +
>  	pkg.tx_oob.s_oob.vcq_num = cq->gdma_id;
>  	pkg.tx_oob.s_oob.vsq_frame = txq->vsq_frame;
>  
> @@ -402,8 +418,6 @@ netdev_tx_t mana_start_xmit(struct sk_buff *skb, struct net_device *ndev)
>  		}
>  	}
>  
> -	WARN_ON_ONCE(pkg.wqe_req.num_sge > MAX_TX_WQE_SGL_ENTRIES);
> -
>  	if (pkg.wqe_req.num_sge <= ARRAY_SIZE(pkg.sgl_array)) {
>  		pkg.wqe_req.sgl = pkg.sgl_array;
>  	} else {
> @@ -438,9 +452,13 @@ netdev_tx_t mana_start_xmit(struct sk_buff *skb, struct net_device *ndev)
>  
>  	if (err) {
>  		(void)skb_dequeue_tail(&txq->pending_skbs);
> +		mana_unmap_skb(skb, apc);
>  		netdev_warn(ndev, "Failed to post TX OOB: %d\n", err);

You have a print right here and in the callee. This condition must
(almost) never happen in practice. It's likely fine to just drop
the packet.

Either way -- this should be a separate patch.

> -		err = NETDEV_TX_BUSY;
> -		goto tx_busy;
> +		if (err == -ENOSPC) {
> +			err = NETDEV_TX_BUSY;
> +			goto tx_busy;
> +		}
> +		goto free_sgl_ptr;
>  	}
>  
>  	err = NETDEV_TX_OK;
> @@ -478,6 +496,25 @@ netdev_tx_t mana_start_xmit(struct sk_buff *skb, struct net_device *ndev)
>  	return NETDEV_TX_OK;
>  }
-- 
pw-bot: cr