From: Neal Cardwell Date: Fri, 29 May 2015 17:47:07 +0000 (-0400) Subject: tcp: fix child sockets to use system default congestion control if not set X-Git-Tag: v3.18.17~67 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=189debb56afd572f29cbd35abea68b4391185627;p=thirdparty%2Fkernel%2Fstable.git tcp: fix child sockets to use system default congestion control if not set [ Upstream commit 9f950415e4e28e7cfae2e416b43e862e8101d996 ] Linux 3.17 and earlier are explicitly engineered so that if the app doesn't specifically request a CC module on a listener before the SYN arrives, then the child gets the system default CC when the connection is established. See tcp_init_congestion_control() in 3.17 or earlier, which says "if no choice made yet assign the current value set as default". The change ("net: tcp: assign tcp cong_ops when tcp sk is created") altered these semantics, so that children got their parent listener's congestion control even if the system default had changed after the listener was created. This commit returns to those original semantics from 3.17 and earlier, since they are the original semantics from 2007 in 4d4d3d1e8 ("[TCP]: Congestion control initialization."), and some Linux congestion control workflows depend on that. In summary, if a listener socket specifically sets TCP_CONGESTION to "x", or the route locks the CC module to "x", then the child gets "x". Otherwise the child gets current system default from net.ipv4.tcp_congestion_control. That's the behavior in 3.17 and earlier, and this commit restores that. Fixes: 55d8694fa82c ("net: tcp: assign tcp cong_ops when tcp sk is created") Cc: Florian Westphal Cc: Daniel Borkmann Cc: Glenn Judd Cc: Stephen Hemminger Signed-off-by: Neal Cardwell Signed-off-by: Eric Dumazet Signed-off-by: Yuchung Cheng Acked-by: Daniel Borkmann Signed-off-by: David S. Miller Signed-off-by: Sasha Levin --- diff --git a/include/net/inet_connection_sock.h b/include/net/inet_connection_sock.h index 848e85cb5c612..24d5c099d3ac4 100644 --- a/include/net/inet_connection_sock.h +++ b/include/net/inet_connection_sock.h @@ -98,7 +98,8 @@ struct inet_connection_sock { const struct tcp_congestion_ops *icsk_ca_ops; const struct inet_connection_sock_af_ops *icsk_af_ops; unsigned int (*icsk_sync_mss)(struct sock *sk, u32 pmtu); - __u8 icsk_ca_state; + __u8 icsk_ca_state:7, + icsk_ca_setsockopt:1; __u8 icsk_retransmits; __u8 icsk_pending; __u8 icsk_backoff; diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c index b1c5970d47a1b..b3316c8279a00 100644 --- a/net/ipv4/tcp_cong.c +++ b/net/ipv4/tcp_cong.c @@ -248,9 +248,10 @@ int tcp_set_congestion_control(struct sock *sk, const char *name) ca = tcp_ca_find(name); /* no change asking for existing value */ - if (ca == icsk->icsk_ca_ops) + if (ca == icsk->icsk_ca_ops) { + icsk->icsk_ca_setsockopt = 1; goto out; - + } #ifdef CONFIG_MODULES /* not found attempt to autoload module */ if (!ca && capable(CAP_NET_ADMIN)) { @@ -273,6 +274,7 @@ int tcp_set_congestion_control(struct sock *sk, const char *name) else { tcp_cleanup_congestion_control(sk); icsk->icsk_ca_ops = ca; + icsk->icsk_ca_setsockopt = 1; if (sk->sk_state != TCP_CLOSE && icsk->icsk_ca_ops->init) icsk->icsk_ca_ops->init(sk); diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c index 71d001dcf2f87..2f6667116e85d 100644 --- a/net/ipv4/tcp_minisocks.c +++ b/net/ipv4/tcp_minisocks.c @@ -451,7 +451,8 @@ struct sock *tcp_create_openreq_child(struct sock *sk, struct request_sock *req, newtp->snd_cwnd = TCP_INIT_CWND; newtp->snd_cwnd_cnt = 0; - if (!try_module_get(newicsk->icsk_ca_ops->owner)) + if (!newicsk->icsk_ca_setsockopt || + !try_module_get(newicsk->icsk_ca_ops->owner)) tcp_assign_congestion_control(newsk); tcp_set_ca_state(newsk, TCP_CA_Open);