Re: [PATCH 1/6] tcp: FIN flags have to be retransmitted as well

[David Gibson <david@gibson.dropbear.id.au>]

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On Fri, Aug 15, 2025 at 06:10:37PM +0200, Stefano Brivio wrote:
> If we're retransmitting any data, and we sent a FIN segment to our
> peer, regardless of whether it was received, we obviously have to
> retransmit it as well, given that it can only come with the last data
> segment, or after it.
> 
> Unconditionally clear the internal TAP_FIN_SENT flag whenever we
> re-transmit, so that we know we have to send it again, in case.
> 
> Reported-by: Paul Holzinger <pholzing@redhat.com>
> Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

> ---
>  tcp.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/tcp.c b/tcp.c
> index 957b498..7c1f237 100644
> --- a/tcp.c
> +++ b/tcp.c
> @@ -1759,6 +1759,7 @@ static int tcp_data_from_tap(const struct ctx *c, struct tcp_tap_conn *conn,
>  			   "fast re-transmit, ACK: %u, previous sequence: %u",
>  			   max_ack_seq, conn->seq_to_tap);
>  		conn->seq_to_tap = max_ack_seq;
> +		conn->events &= ~TAP_FIN_SENT;
>  		if (tcp_set_peek_offset(conn, 0)) {
>  			tcp_rst(c, conn);
>  			return -1;
> @@ -2286,6 +2287,7 @@ void tcp_timer_handler(const struct ctx *c, union epoll_ref ref)
>  			flow_dbg(conn, "ACK timeout, retry");
>  			conn->retrans++;
>  			conn->seq_to_tap = conn->seq_ack_from_tap;
> +			conn->events &= ~TAP_FIN_SENT;
>  			if (!conn->wnd_from_tap)
>  				conn->wnd_from_tap = 1; /* Zero-window probe */
>  			if (tcp_set_peek_offset(conn, 0)) {

-- 
David Gibson (he or they)	| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you, not the other way
				| around.
http://www.ozlabs.org/~dgibson

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