linux-kernel - Re: [RESEND][PATCH v2] myri10ge: remove an unneeded NULL check

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Date:   Tue, 5 Apr 2022 18:25:14 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Xiaomeng Tong <xiam0nd.tong@...il.com>
Cc:     christopher.lee@...i.com, davem@...emloft.net, pabeni@...hat.com,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RESEND][PATCH v2] myri10ge: remove an unneeded NULL check

On Tue,  5 Apr 2022 08:05:53 +0800 Xiaomeng Tong wrote:
> The define of skb_list_walk_safe(first, skb, next_skb) is:
>   for ((skb) = (first), (next_skb) = (skb) ? (skb)->next : NULL; (skb);  \
>      (skb) = (next_skb), (next_skb) = (skb) ? (skb)->next : NULL)
> 
> Thus, if the 'segs' passed as 'first' into the skb_list_walk_safe is NULL,
> the loop will exit immediately. In other words, it can be sure the 'segs'
> is non-NULL when we run inside the loop. So just remove the unnecessary
> NULL check. Also remove the unneeded assignmnets.
> 
> Signed-off-by: Xiaomeng Tong <xiam0nd.tong@...il.com>

The existing code is pretty clearly buggy. Please fix the bugs or don't
touch it. You're obfuscating what the original intention was.

> diff --git a/drivers/net/ethernet/myricom/myri10ge/myri10ge.c b/drivers/net/ethernet/myricom/myri10ge/myri10ge.c
> index 50ac3ee2577a..071657e3dba8 100644
> --- a/drivers/net/ethernet/myricom/myri10ge/myri10ge.c
> +++ b/drivers/net/ethernet/myricom/myri10ge/myri10ge.c
> @@ -2903,12 +2903,8 @@ static netdev_tx_t myri10ge_sw_tso(struct sk_buff *skb,
>  		status = myri10ge_xmit(curr, dev);
>  		if (status != 0) {
>  			dev_kfree_skb_any(curr);
> -			if (segs != NULL) {
> -				curr = segs;
> -				segs = next;
> -				curr->next = NULL;
> -				dev_kfree_skb_any(segs);
> -			}
> +			segs->next = NULL;
> +			dev_kfree_skb_any(next);
>  			goto drop;
>  		}
>  	}