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 <edumazet@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Acked-by: Wei Wang <weiwan@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 5 insertions, 5 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 5def3c48870e..731d3045b50a 100644
--- 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;
                 }
         }