netdev - Re: [PATCH 1/2] Bluetooth: 6LoWPAN: Modify the error handling in the loop

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Date:   Mon, 20 Mar 2023 17:09:11 +0100
From:   Simon Horman <simon.horman@...igine.com>
To:     Jiasheng Jiang <jiasheng@...as.ac.cn>
Cc:     marcel@...tmann.org, johan.hedberg@...il.com, luiz.dentz@...il.com,
        davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        pabeni@...hat.com, linux-bluetooth@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] Bluetooth: 6LoWPAN: Modify the error handling in the
 loop

On Mon, Mar 20, 2023 at 02:31:55PM +0800, Jiasheng Jiang wrote:
> Return the error when send_pkt fails in order to avoid the error being
> overwritten.
> Moreover, remove the redundant 'ret'.
> 
> Fixes: 9c238ca8ec79 ("Bluetooth: 6lowpan: Check transmit errors for multicast packets")
> Signed-off-by: Jiasheng Jiang <jiasheng@...as.ac.cn>

I see that the error handling is imperfect - only the most recent
error value is returned.

But I think this patch introduces a behavioural change: if
an error occurs then no attempt is made to send the
multicast packet to devices that follow in the list of peers.

If so, I'd want to be sure that behaviour is desirable.

> ---
>  net/bluetooth/6lowpan.c | 10 ++++------
>  1 file changed, 4 insertions(+), 6 deletions(-)
> 
> diff --git a/net/bluetooth/6lowpan.c b/net/bluetooth/6lowpan.c
> index 4eb1b3ced0d2..bd6dbca5747f 100644
> --- a/net/bluetooth/6lowpan.c
> +++ b/net/bluetooth/6lowpan.c
> @@ -474,22 +474,20 @@ static int send_mcast_pkt(struct sk_buff *skb, struct net_device *netdev)
>  		dev = lowpan_btle_dev(entry->netdev);
>  
>  		list_for_each_entry_rcu(pentry, &dev->peers, list) {
> -			int ret;
> -
>  			local_skb = skb_clone(skb, GFP_ATOMIC);
>  
>  			BT_DBG("xmit %s to %pMR type %u IP %pI6c chan %p",
>  			       netdev->name,
>  			       &pentry->chan->dst, pentry->chan->dst_type,
>  			       &pentry->peer_addr, pentry->chan);
> -			ret = send_pkt(pentry->chan, local_skb, netdev);
> -			if (ret < 0)
> -				err = ret;
> -
> +			err = send_pkt(pentry->chan, local_skb, netdev);
>  			kfree_skb(local_skb);
> +			if (err < 0)
> +				goto out;
>  		}
>  	}
>  
> +out:
>  	rcu_read_unlock();
>  
>  	return err;
> -- 
> 2.25.1
>