3.16.81-rc1 review patch. If anyone has any objections, please let me know.
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From: Eric Dumazet edumazet@google.com
commit 5ea8ea2cb7f1d0db15762c9b0bb9e7330425a071 upstream.
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 ycheng@google.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Arnd Bergmann arnd@arndb.de [bwh: Backported to 3.16: Apply TCP changes in both tcp_ipv4.c and tcp_ipv6.c] Signed-off-by: Ben Hutchings ben@decadent.org.uk --- --- a/include/net/inet_connection_sock.h +++ b/include/net/inet_connection_sock.h @@ -287,11 +287,6 @@ static inline int inet_csk_reqsk_queue_l return reqsk_queue_len(&inet_csk(sk)->icsk_accept_queue); }
-static inline int inet_csk_reqsk_queue_young(const struct sock *sk) -{ - return reqsk_queue_len_young(&inet_csk(sk)->icsk_accept_queue); -} - static inline int inet_csk_reqsk_queue_is_full(const struct sock *sk) { return reqsk_queue_is_full(&inet_csk(sk)->icsk_accept_queue); --- a/net/dccp/ipv4.c +++ b/net/dccp/ipv4.c @@ -621,13 +621,7 @@ int dccp_v4_conn_request(struct sock *sk if (inet_csk_reqsk_queue_is_full(sk)) goto drop;
- /* - * Accept backlog is full. If we have already queued enough - * of warm entries in syn queue, drop request. It is better than - * clogging syn queue with openreqs with exponentially increasing - * timeout. - */ - if (sk_acceptq_is_full(sk) && inet_csk_reqsk_queue_young(sk) > 1) + if (sk_acceptq_is_full(sk)) goto drop;
req = inet_reqsk_alloc(&dccp_request_sock_ops); --- a/net/dccp/ipv6.c +++ b/net/dccp/ipv6.c @@ -391,7 +391,7 @@ static int dccp_v6_conn_request(struct s if (inet_csk_reqsk_queue_is_full(sk)) goto drop;
- if (sk_acceptq_is_full(sk) && inet_csk_reqsk_queue_young(sk) > 1) + if (sk_acceptq_is_full(sk)) goto drop;
req = inet6_reqsk_alloc(&dccp6_request_sock_ops); --- a/net/ipv4/tcp_ipv4.c +++ b/net/ipv4/tcp_ipv4.c @@ -1292,12 +1292,7 @@ int tcp_v4_conn_request(struct sock *sk, goto drop; }
- /* Accept backlog is full. If we have already queued enough - * of warm entries in syn queue, drop request. It is better than - * clogging syn queue with openreqs with exponentially increasing - * timeout. - */ - if (sk_acceptq_is_full(sk) && inet_csk_reqsk_queue_young(sk) > 1) { + if (sk_acceptq_is_full(sk)) { NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS); goto drop; } --- a/net/ipv6/tcp_ipv6.c +++ b/net/ipv6/tcp_ipv6.c @@ -1009,7 +1009,7 @@ static int tcp_v6_conn_request(struct so goto drop; }
- if (sk_acceptq_is_full(sk) && inet_csk_reqsk_queue_young(sk) > 1) { + if (sk_acceptq_is_full(sk)) { NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS); goto drop; }