releases/4.14.114/tcp-tcp_grow_window-needs-to-respect-tcp_space.patch

   1 From foo@baz Tue 23 Apr 2019 05:18:29 PM CEST
   2 From: Eric Dumazet <edumazet@google.com>
   3 Date: Tue, 16 Apr 2019 10:55:20 -0700
   4 Subject: tcp: tcp_grow_window() needs to respect tcp_space()
   5
   6 From: Eric Dumazet <edumazet@google.com>
   7
   8 [ Upstream commit 50ce163a72d817a99e8974222dcf2886d5deb1ae ]
   9
  10 For some reason, tcp_grow_window() correctly tests if enough room
  11 is present before attempting to increase tp->rcv_ssthresh,
  12 but does not prevent it to grow past tcp_space()
  13
  14 This is causing hard to debug issues, like failing
  15 the (__tcp_select_window(sk) >= tp->rcv_wnd) test
  16 in __tcp_ack_snd_check(), causing ACK delays and possibly
  17 slow flows.
  18
  19 Depending on tcp_rmem[2], MTU, skb->len/skb->truesize ratio,
  20 we can see the problem happening on "netperf -t TCP_RR -- -r 2000,2000"
  21 after about 60 round trips, when the active side no longer sends
  22 immediate acks.
  23
  24 This bug predates git history.
  25
  26 Signed-off-by: Eric Dumazet <edumazet@google.com>
  27 Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
  28 Acked-by: Neal Cardwell <ncardwell@google.com>
  29 Acked-by: Wei Wang <weiwan@google.com>
  30 Signed-off-by: David S. Miller <davem@davemloft.net>
  31 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  32 ---
  33  net/ipv4/tcp_input.c |   10 +++++-----
  34  1 file changed, 5 insertions(+), 5 deletions(-)
  35
  36 --- a/net/ipv4/tcp_input.c
  37 +++ b/net/ipv4/tcp_input.c
  38 @@ -389,11 +389,12 @@ static int __tcp_grow_window(const struc
  39  static void tcp_grow_window(struct sock *sk, const struct sk_buff *skb)
  40  {
  41         struct tcp_sock *tp = tcp_sk(sk);
  42 +       int room;
  43 +
  44 +       room = min_t(int, tp->window_clamp, tcp_space(sk)) - tp->rcv_ssthresh;
  45
  46         /* Check #1 */
  47 -       if (tp->rcv_ssthresh < tp->window_clamp &&
  48 -           (int)tp->rcv_ssthresh < tcp_space(sk) &&
  49 -           !tcp_under_memory_pressure(sk)) {
  50 +       if (room > 0 && !tcp_under_memory_pressure(sk)) {
  51                 int incr;
  52
  53                 /* Check #2. Increase window, if skb with such overhead
  54 @@ -406,8 +407,7 @@ static void tcp_grow_window(struct sock
  55
  56                 if (incr) {
  57                         incr = max_t(int, incr, 2 * skb->len);
  58 -                       tp->rcv_ssthresh = min(tp->rcv_ssthresh + incr,
  59 -                                              tp->window_clamp);
  60 +                       tp->rcv_ssthresh += min(room, incr);
  61                         inet_csk(sk)->icsk_ack.quick |= 1;
  62                 }
  63         }