Commit 6728c617 authored Apr 16, 2019 by Eric Dumazet Committed by Greg Kroah-Hartman Apr 27, 2019

tcp: tcp_grow_window() needs to respect tcp_space()



[ 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>

parent 1cd87883

net/ipv4/tcp_input.c

+5 −5

Original line number	Diff line number	Diff line
		@@ -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;
		}
		}