On Fri, Mar 22, 2019 at 04:44:09PM +0100, Arnd Bergmann wrote:

From: Eric Dumazet <edumazet@google.com>

Per listen(fd, backlog) rules, there is really no point accepting a SYN,
sending a SYNACK, and dropping the following ACK packet if accept queue
is full, because application is not draining accept queue fast enough.

This behavior is fooling TCP clients that believe they established a
flow, while there is nothing at server side. They might then send about
10 MSS (if using IW10) that will be dropped anyway while server is under
stress.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Acked-by: Yuchung Cheng <redacted>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit 5ea8ea2cb7f1d0db15762c9b0bb9e7330425a071)

Also queued up for 4.9.y