tcp: tcp_grow_window() needs to respect tcp_space()

For some reason, tcp_grow_window() correctly tests if enough room is present before attempting to increase tp->rcv_ssthresh, but does not prevent it to grow past tcp_space() This is causing hard to debug issues, like failing the (__tcp_select_window(sk) >= tp->rcv_wnd) test in __tcp_ack_snd_check(), causing ACK delays and possibly slow flows. Depending on tcp_rmem[2], MTU, skb->len/skb->truesize ratio, we can see the problem happening on "netperf -t TCP_RR -- -r 2000,2000" after about 60 round trips, when the active side no longer sends immediate acks. This bug predates git history. Signed-off-by: Eric Dumazet <[email protected]> Acked-by: Soheil Hassas Yeganeh <[email protected]> Acked-by: Neal Cardwell <[email protected]> Acked-by: Wei Wang <[email protected]> Signed-off-by: David S. Miller <[email protected]>
chewitt · Apr 17, 2019 · 50ce163 · 50ce163
1 parent 1e1caa9
commit 50ce163
Showing 1 changed file with 5 additions and 5 deletions.
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
@@ -402,11 +402,12 @@ static int __tcp_grow_window(const struct sock *sk, const struct sk_buff *skb)
 static void tcp_grow_window(struct sock *sk, const struct sk_buff *skb)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
+	int room;
+
+	room = min_t(int, tp->window_clamp, tcp_space(sk)) - tp->rcv_ssthresh;
 
 	/* Check #1 */
-	if (tp->rcv_ssthresh < tp->window_clamp &&
-	    (int)tp->rcv_ssthresh < tcp_space(sk) &&
-	    !tcp_under_memory_pressure(sk)) {
+	if (room > 0 && !tcp_under_memory_pressure(sk)) {
 		int incr;
 
 		/* Check #2. Increase window, if skb with such overhead
@@ -419,8 +420,7 @@ static void tcp_grow_window(struct sock *sk, const struct sk_buff *skb)
 
 		if (incr) {
 			incr = max_t(int, incr, 2 * skb->len);
-			tp->rcv_ssthresh = min(tp->rcv_ssthresh + incr,
-					       tp->window_clamp);
+			tp->rcv_ssthresh += min(room, incr);
 			inet_csk(sk)->icsk_ack.quick |= 1;
 		}
 	}