From: Eric Dumazet edumazet@google.com
[ Upstream commit 50ce163a72d817a99e8974222dcf2886d5deb1ae ]
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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/ipv4/tcp_input.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-)
--- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -358,11 +358,12 @@ static int __tcp_grow_window(const struc 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) && - !sk_under_memory_pressure(sk)) { + if (room > 0 && !sk_under_memory_pressure(sk)) { int incr;
/* Check #2. Increase window, if skb with such overhead @@ -375,8 +376,7 @@ static void tcp_grow_window(struct sock
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; } }