diff options
| -rw-r--r-- | tcp.c | 29 |
1 files changed, 24 insertions, 5 deletions
@@ -1782,7 +1782,23 @@ static void tcp_clamp_window(const struct ctx *c, struct tcp_tap_conn *conn, wnd <<= conn->ws_from_tap; wnd = MIN(MAX_WINDOW, wnd); - if (conn->flags & WND_CLAMPED) { + /* TODO: With (at least) Linux kernel versions 6.1 to 6.5, if we end up + * with a zero-sized window on a TCP socket, dropping data (once + * acknowledged by the guest) with recv() and MSG_TRUNC doesn't appear + * to be enough to make the kernel advertise a non-zero window to the + * sender. Forcing a TCP_WINDOW_CLAMP setting, even with the existing + * value, fixes this. + * + * The STALLED flag on a connection is a sufficient indication that we + * might have a zero-sized window on the socket, because it's set if we + * exhausted the tap-side window, or if everything we receive from a + * socket is already in flight to the guest. + * + * So, if STALLED is set, and we received a window value from the tap, + * force a TCP_WINDOW_CLAMP setsockopt(). This should be investigated + * further and fixed in the kernel instead, if confirmed. + */ + if (!(conn->flags & STALLED) && conn->flags & WND_CLAMPED) { if (prev_scaled == wnd) return; @@ -2405,12 +2421,12 @@ static int tcp_data_from_tap(struct ctx *c, struct tcp_tap_conn *conn, i = keep - 1; } - tcp_clamp_window(c, conn, max_ack_seq_wnd); - /* On socket flush failure, pretend there was no ACK, try again later */ if (ack && !tcp_sock_consume(conn, max_ack_seq)) tcp_update_seqack_from_tap(c, conn, max_ack_seq); + tcp_clamp_window(c, conn, max_ack_seq_wnd); + if (retr) { trace("TCP: fast re-transmit, ACK: %u, previous sequence: %u", max_ack_seq, conn->seq_to_tap); @@ -2568,8 +2584,6 @@ int tcp_tap_handler(struct ctx *c, int af, const void *saddr, const void *daddr, if (th->ack && !(conn->events & ESTABLISHED)) tcp_update_seqack_from_tap(c, conn, ntohl(th->ack_seq)); - conn_flag(c, conn, ~STALLED); - /* Establishing connection from socket */ if (conn->events & SOCK_ACCEPTED) { if (th->syn && th->ack && !th->fin) { @@ -2624,6 +2638,11 @@ int tcp_tap_handler(struct ctx *c, int af, const void *saddr, const void *daddr, if (count == -1) goto reset; + /* Note: STALLED matters for tcp_clamp_window(): unset it only after + * processing data (and window) from the tap side + */ + conn_flag(c, conn, ~STALLED); + if (conn->seq_ack_to_tap != conn->seq_from_tap) ack_due = 1; |