A window shrunk to zero means by definition that anything else that
might be in flight is now out of window. Restart from the currently
acknowledged sequence.
Suggested-by: Jon Maloy
Signed-off-by: Stefano Brivio
---
tcp.c | 25 ++++++++++++++++---------
1 file changed, 16 insertions(+), 9 deletions(-)
diff --git a/tcp.c b/tcp.c
index 1402ca2..dda0a2e 100644
--- a/tcp.c
+++ b/tcp.c
@@ -1257,19 +1257,25 @@ static void tcp_get_tap_ws(struct tcp_tap_conn *conn,
/**
* tcp_tap_window_update() - Process an updated window from tap side
+ * @c: Execution context
* @conn: Connection pointer
* @wnd: Window value, host order, unscaled
*/
-static void tcp_tap_window_update(struct tcp_tap_conn *conn, unsigned wnd)
+static void tcp_tap_window_update(const struct ctx *c,
+ struct tcp_tap_conn *conn, unsigned wnd)
{
wnd = MIN(MAX_WINDOW, wnd << conn->ws_from_tap);
/* Work-around for bug introduced in peer kernel code, commit
- * e2142825c120 ("net: tcp: send zero-window ACK when no memory").
- * We don't update if window shrank to zero.
+ * e2142825c120 ("net: tcp: send zero-window ACK when no memory"): don't
+ * update the window if it shrank to zero, so that we'll eventually
+ * retry to send data, but rewind the sequence as that obviously implies
+ * that no data beyond the updated window will ever be acknowledged.
*/
- if (!wnd && SEQ_LT(conn->seq_ack_from_tap, conn->seq_to_tap))
+ if (!wnd && SEQ_LT(conn->seq_ack_from_tap, conn->seq_to_tap)) {
+ tcp_rewind_seq(c, conn);
return;
+ }
conn->wnd_from_tap = MIN(wnd >> conn->ws_from_tap, USHRT_MAX);
@@ -1694,7 +1700,8 @@ static int tcp_data_from_tap(const struct ctx *c, struct tcp_tap_conn *conn,
tcp_timer_ctl(c, conn);
if (p->count == 1) {
- tcp_tap_window_update(conn, ntohs(th->window));
+ tcp_tap_window_update(c, conn,
+ ntohs(th->window));
return 1;
}
@@ -1772,7 +1779,7 @@ static int tcp_data_from_tap(const struct ctx *c, struct tcp_tap_conn *conn,
if (ack && !tcp_sock_consume(conn, max_ack_seq))
tcp_update_seqack_from_tap(c, conn, max_ack_seq);
- tcp_tap_window_update(conn, max_ack_seq_wnd);
+ tcp_tap_window_update(c, conn, max_ack_seq_wnd);
if (retr) {
flow_trace(conn,
@@ -1861,7 +1868,7 @@ static void tcp_conn_from_sock_finish(const struct ctx *c,
const struct tcphdr *th,
const char *opts, size_t optlen)
{
- tcp_tap_window_update(conn, ntohs(th->window));
+ tcp_tap_window_update(c, conn, ntohs(th->window));
tcp_get_tap_ws(conn, opts, optlen);
/* First value is not scaled */
@@ -2059,7 +2066,7 @@ int tcp_tap_handler(const struct ctx *c, uint8_t pif, sa_family_t af,
if (!th->ack)
goto reset;
- tcp_tap_window_update(conn, ntohs(th->window));
+ tcp_tap_window_update(c, conn, ntohs(th->window));
tcp_data_from_sock(c, conn);
@@ -2071,7 +2078,7 @@ int tcp_tap_handler(const struct ctx *c, uint8_t pif, sa_family_t af,
if (conn->events & TAP_FIN_RCVD) {
tcp_sock_consume(conn, ntohl(th->ack_seq));
tcp_update_seqack_from_tap(c, conn, ntohl(th->ack_seq));
- tcp_tap_window_update(conn, ntohs(th->window));
+ tcp_tap_window_update(c, conn, ntohs(th->window));
tcp_data_from_sock(c, conn);
if (conn->events & SOCK_FIN_RCVD &&
--
2.43.0