netdev - Re: [PATCH] net: ipv4: tcp.c: fix an assignment in an if condition

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Date:   Sat, 12 Mar 2022 09:19:36 -0800
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     Alexander Vorwerk <alexander.vorwerk@...d.uni-goettingen.de>
Cc:     <edumazet@...gle.com>, <davem@...emloft.net>,
        <yoshfuji@...ux-ipv6.org>, <dsahern@...nel.org>, <kuba@...nel.org>,
        <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] net: ipv4: tcp.c: fix an assignment in an if condition

On Sat, 12 Mar 2022 17:27:44 +0100
Alexander Vorwerk <alexander.vorwerk@...d.uni-goettingen.de> wrote:

> reported by checkpatch.pl
> 
> Signed-off-by: Alexander Vorwerk <alexander.vorwerk@...d.uni-goettingen.de>
> ---
>  net/ipv4/tcp.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index 28ff2a820f7c..7fa6e7e6ea80 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -959,10 +959,10 @@ static struct sk_buff *tcp_build_frag(struct sock *sk, int size_goal, int flags,
>  	struct sk_buff *skb = tcp_write_queue_tail(sk);
>  	struct tcp_sock *tp = tcp_sk(sk);
>  	bool can_coalesce;
> -	int copy, i;
> +	int copy = size_goal - skb->len;
> +	int i;
>  
> -	if (!skb || (copy = size_goal - skb->len) <= 0 ||
> -	    !tcp_skb_can_collapse_to(skb)) {
> +	if (!skb || copy <= 0 || !tcp_skb_can_collapse_to(skb)) {
>  new_segment:
>  		if (!sk_stream_memory_free(sk))
>  			return NULL;

Your new code will crash if skb is NULL.