Re: [PATCH net-next] tcp: remove dead code in tcp_rcv_state_process()

[Xuanqiang Luo <xuanqiang.luo@linux.dev>]

On 2026/9/22 at 09:06 Eric Dumazet wrote:
> Since commit 3d501dd326fb ("tcp: do not accept ACK of bytes we never
> sent"), tcp_ack() bounds the acceptable old ACK window by
> min(tp->max_window, tp->bytes_acked).
> 
> When sk->sk_state == TCP_SYN_RECV, tp->bytes_acked is always 0, so
> any segment with before(ack, prior_snd_una) immediately returns
> -SKB_DROP_REASON_TCP_TOO_OLD_ACK and never reaches the old_ack label
> (which returns 0).
> 
> Therefore, tcp_ack() can only return 0 in closing states (where old
> ACKs are accepted), and can never return 0 in TCP_SYN_RECV.
> 
> Simplify the tcp_ack() return value check in tcp_rcv_state_process()
> to only check for negative return values and remove the unreachable
> !reason branch.
> 
> Signed-off-by: Eric Dumazet <edumazet@google.com>

Reviewed-by: Xuanqiang Luo <luoxuanqiang@kylinos.cn>

Thanks,
Xuanqiang