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![Eric Dumazet](/assets/img/avatar_default.png)
One of the major issue for TCP is the SYNACK rtx handling, done by inet_csk_reqsk_queue_prune(), fired by the keepalive timer of a TCP_LISTEN socket. This function runs for awful long times, with socket lock held, meaning that other cpus needing this lock have to spin for hundred of ms. SYNACK are sent in huge bursts, likely to cause severe drops anyway. This model was OK 15 years ago when memory was very tight. We now can afford to have a timer per request sock. Timer invocations no longer need to lock the listener, and can be run from all cpus in parallel. With following patch increasing somaxconn width to 32 bits, I tested a listener with more than 4 million active request sockets, and a steady SYNFLOOD of ~200,000 SYN per second. Host was sending ~830,000 SYNACK per second. This is ~100 times more what we could achieve before this patch. Later, we will get rid of the listener hash and use ehash instead. Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
271 lines
7.1 KiB
C
271 lines
7.1 KiB
C
/*
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* net/dccp/timer.c
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*
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* An implementation of the DCCP protocol
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* Arnaldo Carvalho de Melo <acme@conectiva.com.br>
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version
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* 2 of the License, or (at your option) any later version.
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*/
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#include <linux/dccp.h>
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#include <linux/skbuff.h>
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#include <linux/export.h>
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#include "dccp.h"
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/* sysctl variables governing numbers of retransmission attempts */
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int sysctl_dccp_request_retries __read_mostly = TCP_SYN_RETRIES;
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int sysctl_dccp_retries1 __read_mostly = TCP_RETR1;
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int sysctl_dccp_retries2 __read_mostly = TCP_RETR2;
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static void dccp_write_err(struct sock *sk)
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{
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sk->sk_err = sk->sk_err_soft ? : ETIMEDOUT;
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sk->sk_error_report(sk);
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dccp_send_reset(sk, DCCP_RESET_CODE_ABORTED);
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dccp_done(sk);
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DCCP_INC_STATS_BH(DCCP_MIB_ABORTONTIMEOUT);
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}
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/* A write timeout has occurred. Process the after effects. */
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static int dccp_write_timeout(struct sock *sk)
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{
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const struct inet_connection_sock *icsk = inet_csk(sk);
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int retry_until;
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if (sk->sk_state == DCCP_REQUESTING || sk->sk_state == DCCP_PARTOPEN) {
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if (icsk->icsk_retransmits != 0)
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dst_negative_advice(sk);
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retry_until = icsk->icsk_syn_retries ?
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: sysctl_dccp_request_retries;
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} else {
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if (icsk->icsk_retransmits >= sysctl_dccp_retries1) {
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/* NOTE. draft-ietf-tcpimpl-pmtud-01.txt requires pmtu
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black hole detection. :-(
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It is place to make it. It is not made. I do not want
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to make it. It is disguisting. It does not work in any
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case. Let me to cite the same draft, which requires for
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us to implement this:
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"The one security concern raised by this memo is that ICMP black holes
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are often caused by over-zealous security administrators who block
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all ICMP messages. It is vitally important that those who design and
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deploy security systems understand the impact of strict filtering on
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upper-layer protocols. The safest web site in the world is worthless
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if most TCP implementations cannot transfer data from it. It would
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be far nicer to have all of the black holes fixed rather than fixing
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all of the TCP implementations."
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Golden words :-).
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*/
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dst_negative_advice(sk);
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}
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retry_until = sysctl_dccp_retries2;
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/*
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* FIXME: see tcp_write_timout and tcp_out_of_resources
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*/
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}
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if (icsk->icsk_retransmits >= retry_until) {
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/* Has it gone just too far? */
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dccp_write_err(sk);
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return 1;
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}
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return 0;
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}
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/*
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* The DCCP retransmit timer.
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*/
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static void dccp_retransmit_timer(struct sock *sk)
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{
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struct inet_connection_sock *icsk = inet_csk(sk);
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/*
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* More than than 4MSL (8 minutes) has passed, a RESET(aborted) was
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* sent, no need to retransmit, this sock is dead.
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*/
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if (dccp_write_timeout(sk))
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return;
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/*
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* We want to know the number of packets retransmitted, not the
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* total number of retransmissions of clones of original packets.
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*/
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if (icsk->icsk_retransmits == 0)
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DCCP_INC_STATS_BH(DCCP_MIB_TIMEOUTS);
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if (dccp_retransmit_skb(sk) != 0) {
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/*
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* Retransmission failed because of local congestion,
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* do not backoff.
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*/
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if (--icsk->icsk_retransmits == 0)
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icsk->icsk_retransmits = 1;
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inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
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min(icsk->icsk_rto,
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TCP_RESOURCE_PROBE_INTERVAL),
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DCCP_RTO_MAX);
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return;
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}
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icsk->icsk_backoff++;
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icsk->icsk_rto = min(icsk->icsk_rto << 1, DCCP_RTO_MAX);
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inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, icsk->icsk_rto,
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DCCP_RTO_MAX);
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if (icsk->icsk_retransmits > sysctl_dccp_retries1)
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__sk_dst_reset(sk);
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}
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static void dccp_write_timer(unsigned long data)
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{
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struct sock *sk = (struct sock *)data;
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struct inet_connection_sock *icsk = inet_csk(sk);
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int event = 0;
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bh_lock_sock(sk);
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if (sock_owned_by_user(sk)) {
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/* Try again later */
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sk_reset_timer(sk, &icsk->icsk_retransmit_timer,
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jiffies + (HZ / 20));
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goto out;
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}
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if (sk->sk_state == DCCP_CLOSED || !icsk->icsk_pending)
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goto out;
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if (time_after(icsk->icsk_timeout, jiffies)) {
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sk_reset_timer(sk, &icsk->icsk_retransmit_timer,
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icsk->icsk_timeout);
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goto out;
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}
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event = icsk->icsk_pending;
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icsk->icsk_pending = 0;
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switch (event) {
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case ICSK_TIME_RETRANS:
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dccp_retransmit_timer(sk);
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break;
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}
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out:
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bh_unlock_sock(sk);
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sock_put(sk);
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}
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static void dccp_keepalive_timer(unsigned long data)
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{
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struct sock *sk = (struct sock *)data;
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pr_err("dccp should not use a keepalive timer !\n");
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sock_put(sk);
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}
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/* This is the same as tcp_delack_timer, sans prequeue & mem_reclaim stuff */
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static void dccp_delack_timer(unsigned long data)
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{
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struct sock *sk = (struct sock *)data;
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struct inet_connection_sock *icsk = inet_csk(sk);
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bh_lock_sock(sk);
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if (sock_owned_by_user(sk)) {
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/* Try again later. */
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icsk->icsk_ack.blocked = 1;
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NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED);
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sk_reset_timer(sk, &icsk->icsk_delack_timer,
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jiffies + TCP_DELACK_MIN);
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goto out;
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}
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if (sk->sk_state == DCCP_CLOSED ||
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!(icsk->icsk_ack.pending & ICSK_ACK_TIMER))
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goto out;
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if (time_after(icsk->icsk_ack.timeout, jiffies)) {
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sk_reset_timer(sk, &icsk->icsk_delack_timer,
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icsk->icsk_ack.timeout);
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goto out;
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}
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icsk->icsk_ack.pending &= ~ICSK_ACK_TIMER;
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if (inet_csk_ack_scheduled(sk)) {
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if (!icsk->icsk_ack.pingpong) {
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/* Delayed ACK missed: inflate ATO. */
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icsk->icsk_ack.ato = min(icsk->icsk_ack.ato << 1,
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icsk->icsk_rto);
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} else {
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/* Delayed ACK missed: leave pingpong mode and
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* deflate ATO.
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*/
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icsk->icsk_ack.pingpong = 0;
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icsk->icsk_ack.ato = TCP_ATO_MIN;
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}
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dccp_send_ack(sk);
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NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKS);
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}
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out:
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bh_unlock_sock(sk);
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sock_put(sk);
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}
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/**
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* dccp_write_xmitlet - Workhorse for CCID packet dequeueing interface
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* See the comments above %ccid_dequeueing_decision for supported modes.
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*/
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static void dccp_write_xmitlet(unsigned long data)
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{
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struct sock *sk = (struct sock *)data;
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bh_lock_sock(sk);
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if (sock_owned_by_user(sk))
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sk_reset_timer(sk, &dccp_sk(sk)->dccps_xmit_timer, jiffies + 1);
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else
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dccp_write_xmit(sk);
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bh_unlock_sock(sk);
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}
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static void dccp_write_xmit_timer(unsigned long data)
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{
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dccp_write_xmitlet(data);
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sock_put((struct sock *)data);
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}
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void dccp_init_xmit_timers(struct sock *sk)
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{
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struct dccp_sock *dp = dccp_sk(sk);
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tasklet_init(&dp->dccps_xmitlet, dccp_write_xmitlet, (unsigned long)sk);
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setup_timer(&dp->dccps_xmit_timer, dccp_write_xmit_timer,
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(unsigned long)sk);
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inet_csk_init_xmit_timers(sk, &dccp_write_timer, &dccp_delack_timer,
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&dccp_keepalive_timer);
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}
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static ktime_t dccp_timestamp_seed;
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/**
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* dccp_timestamp - 10s of microseconds time source
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* Returns the number of 10s of microseconds since loading DCCP. This is native
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* DCCP time difference format (RFC 4340, sec. 13).
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* Please note: This will wrap around about circa every 11.9 hours.
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*/
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u32 dccp_timestamp(void)
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{
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u64 delta = (u64)ktime_us_delta(ktime_get_real(), dccp_timestamp_seed);
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do_div(delta, 10);
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return delta;
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}
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EXPORT_SYMBOL_GPL(dccp_timestamp);
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void __init dccp_timestamping_init(void)
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{
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dccp_timestamp_seed = ktime_get_real();
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}
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