tcp: inherit listener congestion control for passive cnx

Rick Jones reported that TCP_CONGESTION sockopt performed on a listener
was ignored for its children sockets : right after accept() the
congestion control for new socket is the system default one.

This seems an oversight of the initial design (quoted from Stephen)

Based on prior investigation and patch from Rick.

Reported-by: Rick Jones <rick.jones2@hp.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
CC: Stephen Hemminger <shemminger@vyatta.com>
CC: Yuchung Cheng <ycheng@google.com>
Tested-by: Rick Jones <rick.jones2@hp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 3 insertions, 0 deletions

diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index b8867061fce4..cb2b1c6a2ce1 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -175,6 +175,9 @@ tcp_congestion_control - STRING
         connections. The algorithm "reno" is always available, but
         additional choices may be available based on kernel configuration.
         Default is set as part of kernel configuration.
+        For passive connections, the listener congestion control choice
+        is inherited.
+        [see setsockopt(listenfd, SOL_TCP, TCP_CONGESTION, "name" ...) ]
 
 tcp_cookie_size - INTEGER
         Default size of TCP Cookie Transactions (TCPCT) option, that may be