[PATCH] tcp: remove redundant check on tskb

[PATCH] tcp: remove redundant check on tskb

[Colin King]

From: Colin Ian King <colin.king@canonical.com>

The non-null check on tskb is always false because it is in an else
path of a check on tskb and hence tskb is null in this code block.
This is check is therefore redundant and can be removed as well
as the label coalesc.

if (tsbk) {
        ...
} else {
        ...
        if (unlikely(!skb)) {
                if (tskb)       /* can never be true, redundant code */
                        goto coalesc;
                return;
        }
}

Addresses-Coverity: ("Logically dead code")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
---
 net/ipv4/tcp_output.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index e265d1aeeb66..32061928b054 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -3088,7 +3088,6 @@ void tcp_send_fin(struct sock *sk)
 		tskb = skb_rb_last(&sk->tcp_rtx_queue);
 
 	if (tskb) {
-coalesce:
 		TCP_SKB_CB(tskb)->tcp_flags |= TCPHDR_FIN;
 		TCP_SKB_CB(tskb)->end_seq++;
 		tp->write_seq++;
@@ -3104,11 +3103,9 @@ void tcp_send_fin(struct sock *sk)
 		}
 	} else {
 		skb = alloc_skb_fclone(MAX_TCP_HEADER, sk->sk_allocation);
-		if (unlikely(!skb)) {
-			if (tskb)
-				goto coalesce;
+		if (unlikely(!skb))
 			return;
-		}
+
 		INIT_LIST_HEAD(&skb->tcp_tsorted_anchor);
 		skb_reserve(skb, MAX_TCP_HEADER);
 		sk_forced_mem_schedule(sk, skb->truesize);
-- 
2.20.1

Re: [PATCH] tcp: remove redundant check on tskb

[Dan Carpenter]

On Thu, Apr 04, 2019 at 03:46:03PM +0100, Colin King wrote:
> From: Colin Ian King <colin.king@canonical.com>
> 
> The non-null check on tskb is always false because it is in an else
> path of a check on tskb and hence tskb is null in this code block.
> This is check is therefore redundant and can be removed as well
> as the label coalesc.
> 
> if (tsbk) {
>         ...
> } else {
>         ...
>         if (unlikely(!skb)) {
>                 if (tskb)       /* can never be true, redundant code */
>                         goto coalesc;
>                 return;
>         }
> }
> 
> Addresses-Coverity: ("Logically dead code")
> Signed-off-by: Colin Ian King <colin.king@canonical.com>

This was fallout from commit 75c119afe14f ("tcp: implement rb-tree based
retransmit queue").

regards,
dan carpenter

Re: [PATCH] tcp: remove redundant check on tskb

[Mukesh Ojha]

On 4/4/2019 8:16 PM, Colin King wrote:
> From: Colin Ian King <colin.king@canonical.com>
>
> The non-null check on tskb is always false because it is in an else
> path of a check on tskb and hence tskb is null in this code block.
> This is check is therefore redundant and can be removed as well
> as the label coalesc.
>
> if (tsbk) {
>          ...
> } else {
>          ...
>          if (unlikely(!skb)) {
>                  if (tskb)       /* can never be true, redundant code */
>                          goto coalesc;
>                  return;
>          }
> }
>
> Addresses-Coverity: ("Logically dead code")
> Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Mukesh Ojha <mojha@codeaurora.org>

Cheers,
-Mukesh
> ---
>   net/ipv4/tcp_output.c | 7 ++-----
>   1 file changed, 2 insertions(+), 5 deletions(-)
>
> diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
> index e265d1aeeb66..32061928b054 100644
> --- a/net/ipv4/tcp_output.c
> +++ b/net/ipv4/tcp_output.c
> @@ -3088,7 +3088,6 @@ void tcp_send_fin(struct sock *sk)
>   		tskb = skb_rb_last(&sk->tcp_rtx_queue);
>   
>   	if (tskb) {
> -coalesce:
>   		TCP_SKB_CB(tskb)->tcp_flags |= TCPHDR_FIN;
>   		TCP_SKB_CB(tskb)->end_seq++;
>   		tp->write_seq++;
> @@ -3104,11 +3103,9 @@ void tcp_send_fin(struct sock *sk)
>   		}
>   	} else {
>   		skb = alloc_skb_fclone(MAX_TCP_HEADER, sk->sk_allocation);
> -		if (unlikely(!skb)) {
> -			if (tskb)
> -				goto coalesce;
> +		if (unlikely(!skb))
>   			return;
> -		}
> +
>   		INIT_LIST_HEAD(&skb->tcp_tsorted_anchor);
>   		skb_reserve(skb, MAX_TCP_HEADER);
>   		sk_forced_mem_schedule(sk, skb->truesize);

Re: [PATCH] tcp: remove redundant check on tskb

[Eric Dumazet]

On Thu, Apr 4, 2019 at 7:46 AM Colin King <colin.king@canonical.com> wrote:
>
> From: Colin Ian King <colin.king@canonical.com>
>
> The non-null check on tskb is always false because it is in an else
> path of a check on tskb and hence tskb is null in this code block.
> This is check is therefore redundant and can be removed as well
> as the label coalesc.
>...

> Addresses-Coverity: ("Logically dead code")
> Signed-off-by: Colin Ian King <colin.king@canonical.com>

SGTM, thanks.

Signed-off-by: Eric Dumazet <edumazet@google.com>

Re: [PATCH] tcp: remove redundant check on tskb

[David Miller]

From: Colin King <colin.king@canonical.com>
Date: Thu,  4 Apr 2019 15:46:03 +0100

> From: Colin Ian King <colin.king@canonical.com>
> 
> The non-null check on tskb is always false because it is in an else
> path of a check on tskb and hence tskb is null in this code block.
> This is check is therefore redundant and can be removed as well
> as the label coalesc.
> 
> if (tsbk) {
>         ...
> } else {
>         ...
>         if (unlikely(!skb)) {
>                 if (tskb)       /* can never be true, redundant code */
>                         goto coalesc;
>                 return;
>         }
> }
> 
> Addresses-Coverity: ("Logically dead code")
> Signed-off-by: Colin Ian King <colin.king@canonical.com>

Applied to net-next.