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

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Message-ID: <82bcd959-571e-42ce-b341-cbfa19f9f86d@linux.microsoft.com>
Date: Wed, 5 Nov 2025 22:10:23 +0530
From: Aditya Garg <gargaditya@...ux.microsoft.com>
To: Jakub Kicinski <kuba@...nel.org>
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 01-11-2025 04:56, Jakub Kicinski wrote:
> 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..
> 
Hi Jakub,
Agreed, The GSO specific warning is redundant. I'll drop it in next 
revision.
>> +		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
> 
Ok
>> +			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.
> The logs placed in callee doesn't covers all the failure scenarios, 
hence I feel to have this log here with proper status. Maybe I can 
remove the log in the callee?

> Either way -- this should be a separate patch.
> 
Are you suggesting a separate patch altogether or two patch in the same 
series?

Based on your suggestion i can work on v3.
Regards,
Aditya

>> -		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;
>>   }