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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Eric Dumazet <edumazet@google.com>,
        Soheil Hassas Yeganeh <soheil@google.com>,
        Yuchung Cheng <ycheng@google.com>,
        "David S. Miller" <davem@davemloft.net>
Subject: [PATCH 4.19 014/142] tcp: Do not underestimate rwnd_limited
Date:   Fri, 14 Dec 2018 12:58:19 +0100
Message-Id: <20181214115747.617053615@linuxfoundation.org>
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4.19-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit 41727549de3e7281feb174d568c6e46823db8684 ]

If available rwnd is too small, tcp_tso_should_defer()
can decide it is worth waiting before splitting a TSO packet.

This really means we are rwnd limited.

Fixes: 5615f88614a4 ("tcp: instrument how long TCP is limited by receive window")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Reviewed-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/ipv4/tcp_output.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2338,8 +2338,11 @@ static bool tcp_write_xmit(struct sock *
 		} else {
 			if (!push_one &&
 			    tcp_tso_should_defer(sk, skb, &is_cwnd_limited,
-						 max_segs))
+						 max_segs)) {
+				if (!is_cwnd_limited)
+					is_rwnd_limited = true;
 				break;
+			}
 		}
 
 		limit = mss_now;