linux/net/ipv4/tcp_timer.c
Damian Lukowski 6fa12c8503 Revert Backoff [v3]: Calculate TCP's connection close threshold as a time value.
RFC 1122 specifies two threshold values R1 and R2 for connection timeouts,
which may represent a number of allowed retransmissions or a timeout value.
Currently linux uses sysctl_tcp_retries{1,2} to specify the thresholds
in number of allowed retransmissions.

For any desired threshold R2 (by means of time) one can specify tcp_retries2
(by means of number of retransmissions) such that TCP will not time out
earlier than R2. This is the case, because the RTO schedule follows a fixed
pattern, namely exponential backoff.

However, the RTO behaviour is not predictable any more if RTO backoffs can be
reverted, as it is the case in the draft
"Make TCP more Robust to Long Connectivity Disruptions"
(http://tools.ietf.org/html/draft-zimmermann-tcp-lcd).

In the worst case TCP would time out a connection after 3.2 seconds, if the
initial RTO equaled MIN_RTO and each backoff has been reverted.

This patch introduces a function retransmits_timed_out(N),
which calculates the timeout of a TCP connection, assuming an initial
RTO of MIN_RTO and N unsuccessful, exponentially backed-off retransmissions.

Whenever timeout decisions are made by comparing the retransmission counter
to some value N, this function can be used, instead.

The meaning of tcp_retries2 will be changed, as many more RTO retransmissions
can occur than the value indicates. However, it yields a timeout which is
similar to the one of an unpatched, exponentially backing off TCP in the same
scenario. As no application could rely on an RTO greater than MIN_RTO, there
should be no risk of a regression.

Signed-off-by: Damian Lukowski <damian@tvk.rwth-aachen.de>
Acked-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: David S. Miller <davem@davemloft.net>
2009-09-01 02:45:47 -07:00

538 lines
14 KiB
C

/*
* INET An implementation of the TCP/IP protocol suite for the LINUX
* operating system. INET is implemented using the BSD Socket
* interface as the means of communication with the user level.
*
* Implementation of the Transmission Control Protocol(TCP).
*
* Authors: Ross Biro
* Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
* Mark Evans, <evansmp@uhura.aston.ac.uk>
* Corey Minyard <wf-rch!minyard@relay.EU.net>
* Florian La Roche, <flla@stud.uni-sb.de>
* Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
* Linus Torvalds, <torvalds@cs.helsinki.fi>
* Alan Cox, <gw4pts@gw4pts.ampr.org>
* Matthew Dillon, <dillon@apollo.west.oic.com>
* Arnt Gulbrandsen, <agulbra@nvg.unit.no>
* Jorge Cwik, <jorge@laser.satlink.net>
*/
#include <linux/module.h>
#include <net/tcp.h>
int sysctl_tcp_syn_retries __read_mostly = TCP_SYN_RETRIES;
int sysctl_tcp_synack_retries __read_mostly = TCP_SYNACK_RETRIES;
int sysctl_tcp_keepalive_time __read_mostly = TCP_KEEPALIVE_TIME;
int sysctl_tcp_keepalive_probes __read_mostly = TCP_KEEPALIVE_PROBES;
int sysctl_tcp_keepalive_intvl __read_mostly = TCP_KEEPALIVE_INTVL;
int sysctl_tcp_retries1 __read_mostly = TCP_RETR1;
int sysctl_tcp_retries2 __read_mostly = TCP_RETR2;
int sysctl_tcp_orphan_retries __read_mostly;
static void tcp_write_timer(unsigned long);
static void tcp_delack_timer(unsigned long);
static void tcp_keepalive_timer (unsigned long data);
void tcp_init_xmit_timers(struct sock *sk)
{
inet_csk_init_xmit_timers(sk, &tcp_write_timer, &tcp_delack_timer,
&tcp_keepalive_timer);
}
EXPORT_SYMBOL(tcp_init_xmit_timers);
static void tcp_write_err(struct sock *sk)
{
sk->sk_err = sk->sk_err_soft ? : ETIMEDOUT;
sk->sk_error_report(sk);
tcp_done(sk);
NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONTIMEOUT);
}
/* Do not allow orphaned sockets to eat all our resources.
* This is direct violation of TCP specs, but it is required
* to prevent DoS attacks. It is called when a retransmission timeout
* or zero probe timeout occurs on orphaned socket.
*
* Criteria is still not confirmed experimentally and may change.
* We kill the socket, if:
* 1. If number of orphaned sockets exceeds an administratively configured
* limit.
* 2. If we have strong memory pressure.
*/
static int tcp_out_of_resources(struct sock *sk, int do_reset)
{
struct tcp_sock *tp = tcp_sk(sk);
int orphans = percpu_counter_read_positive(&tcp_orphan_count);
/* If peer does not open window for long time, or did not transmit
* anything for long time, penalize it. */
if ((s32)(tcp_time_stamp - tp->lsndtime) > 2*TCP_RTO_MAX || !do_reset)
orphans <<= 1;
/* If some dubious ICMP arrived, penalize even more. */
if (sk->sk_err_soft)
orphans <<= 1;
if (tcp_too_many_orphans(sk, orphans)) {
if (net_ratelimit())
printk(KERN_INFO "Out of socket memory\n");
/* Catch exceptional cases, when connection requires reset.
* 1. Last segment was sent recently. */
if ((s32)(tcp_time_stamp - tp->lsndtime) <= TCP_TIMEWAIT_LEN ||
/* 2. Window is closed. */
(!tp->snd_wnd && !tp->packets_out))
do_reset = 1;
if (do_reset)
tcp_send_active_reset(sk, GFP_ATOMIC);
tcp_done(sk);
NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONMEMORY);
return 1;
}
return 0;
}
/* Calculate maximal number or retries on an orphaned socket. */
static int tcp_orphan_retries(struct sock *sk, int alive)
{
int retries = sysctl_tcp_orphan_retries; /* May be zero. */
/* We know from an ICMP that something is wrong. */
if (sk->sk_err_soft && !alive)
retries = 0;
/* However, if socket sent something recently, select some safe
* number of retries. 8 corresponds to >100 seconds with minimal
* RTO of 200msec. */
if (retries == 0 && alive)
retries = 8;
return retries;
}
static void tcp_mtu_probing(struct inet_connection_sock *icsk, struct sock *sk)
{
/* Black hole detection */
if (sysctl_tcp_mtu_probing) {
if (!icsk->icsk_mtup.enabled) {
icsk->icsk_mtup.enabled = 1;
tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
} else {
struct tcp_sock *tp = tcp_sk(sk);
int mss;
mss = tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low) >> 1;
mss = min(sysctl_tcp_base_mss, mss);
mss = max(mss, 68 - tp->tcp_header_len);
icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
}
}
}
/* A write timeout has occurred. Process the after effects. */
static int tcp_write_timeout(struct sock *sk)
{
struct inet_connection_sock *icsk = inet_csk(sk);
int retry_until;
bool do_reset;
if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) {
if (icsk->icsk_retransmits)
dst_negative_advice(&sk->sk_dst_cache);
retry_until = icsk->icsk_syn_retries ? : sysctl_tcp_syn_retries;
} else {
if (retransmits_timed_out(sk, sysctl_tcp_retries1)) {
/* Black hole detection */
tcp_mtu_probing(icsk, sk);
dst_negative_advice(&sk->sk_dst_cache);
}
retry_until = sysctl_tcp_retries2;
if (sock_flag(sk, SOCK_DEAD)) {
const int alive = (icsk->icsk_rto < TCP_RTO_MAX);
retry_until = tcp_orphan_retries(sk, alive);
do_reset = alive ||
!retransmits_timed_out(sk, retry_until);
if (tcp_out_of_resources(sk, do_reset))
return 1;
}
}
if (retransmits_timed_out(sk, retry_until)) {
/* Has it gone just too far? */
tcp_write_err(sk);
return 1;
}
return 0;
}
static void tcp_delack_timer(unsigned long data)
{
struct sock *sk = (struct sock *)data;
struct tcp_sock *tp = tcp_sk(sk);
struct inet_connection_sock *icsk = inet_csk(sk);
bh_lock_sock(sk);
if (sock_owned_by_user(sk)) {
/* Try again later. */
icsk->icsk_ack.blocked = 1;
NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED);
sk_reset_timer(sk, &icsk->icsk_delack_timer, jiffies + TCP_DELACK_MIN);
goto out_unlock;
}
sk_mem_reclaim_partial(sk);
if (sk->sk_state == TCP_CLOSE || !(icsk->icsk_ack.pending & ICSK_ACK_TIMER))
goto out;
if (time_after(icsk->icsk_ack.timeout, jiffies)) {
sk_reset_timer(sk, &icsk->icsk_delack_timer, icsk->icsk_ack.timeout);
goto out;
}
icsk->icsk_ack.pending &= ~ICSK_ACK_TIMER;
if (!skb_queue_empty(&tp->ucopy.prequeue)) {
struct sk_buff *skb;
NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSCHEDULERFAILED);
while ((skb = __skb_dequeue(&tp->ucopy.prequeue)) != NULL)
sk_backlog_rcv(sk, skb);
tp->ucopy.memory = 0;
}
if (inet_csk_ack_scheduled(sk)) {
if (!icsk->icsk_ack.pingpong) {
/* Delayed ACK missed: inflate ATO. */
icsk->icsk_ack.ato = min(icsk->icsk_ack.ato << 1, icsk->icsk_rto);
} else {
/* Delayed ACK missed: leave pingpong mode and
* deflate ATO.
*/
icsk->icsk_ack.pingpong = 0;
icsk->icsk_ack.ato = TCP_ATO_MIN;
}
tcp_send_ack(sk);
NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKS);
}
TCP_CHECK_TIMER(sk);
out:
if (tcp_memory_pressure)
sk_mem_reclaim(sk);
out_unlock:
bh_unlock_sock(sk);
sock_put(sk);
}
static void tcp_probe_timer(struct sock *sk)
{
struct inet_connection_sock *icsk = inet_csk(sk);
struct tcp_sock *tp = tcp_sk(sk);
int max_probes;
if (tp->packets_out || !tcp_send_head(sk)) {
icsk->icsk_probes_out = 0;
return;
}
/* *WARNING* RFC 1122 forbids this
*
* It doesn't AFAIK, because we kill the retransmit timer -AK
*
* FIXME: We ought not to do it, Solaris 2.5 actually has fixing
* this behaviour in Solaris down as a bug fix. [AC]
*
* Let me to explain. icsk_probes_out is zeroed by incoming ACKs
* even if they advertise zero window. Hence, connection is killed only
* if we received no ACKs for normal connection timeout. It is not killed
* only because window stays zero for some time, window may be zero
* until armageddon and even later. We are in full accordance
* with RFCs, only probe timer combines both retransmission timeout
* and probe timeout in one bottle. --ANK
*/
max_probes = sysctl_tcp_retries2;
if (sock_flag(sk, SOCK_DEAD)) {
const int alive = ((icsk->icsk_rto << icsk->icsk_backoff) < TCP_RTO_MAX);
max_probes = tcp_orphan_retries(sk, alive);
if (tcp_out_of_resources(sk, alive || icsk->icsk_probes_out <= max_probes))
return;
}
if (icsk->icsk_probes_out > max_probes) {
tcp_write_err(sk);
} else {
/* Only send another probe if we didn't close things up. */
tcp_send_probe0(sk);
}
}
/*
* The TCP retransmit timer.
*/
void tcp_retransmit_timer(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
struct inet_connection_sock *icsk = inet_csk(sk);
if (!tp->packets_out)
goto out;
WARN_ON(tcp_write_queue_empty(sk));
if (!tp->snd_wnd && !sock_flag(sk, SOCK_DEAD) &&
!((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))) {
/* Receiver dastardly shrinks window. Our retransmits
* become zero probes, but we should not timeout this
* connection. If the socket is an orphan, time it out,
* we cannot allow such beasts to hang infinitely.
*/
#ifdef TCP_DEBUG
struct inet_sock *inet = inet_sk(sk);
if (sk->sk_family == AF_INET) {
LIMIT_NETDEBUG(KERN_DEBUG "TCP: Peer %pI4:%u/%u unexpectedly shrunk window %u:%u (repaired)\n",
&inet->daddr, ntohs(inet->dport),
inet->num, tp->snd_una, tp->snd_nxt);
}
#if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
else if (sk->sk_family == AF_INET6) {
struct ipv6_pinfo *np = inet6_sk(sk);
LIMIT_NETDEBUG(KERN_DEBUG "TCP: Peer %pI6:%u/%u unexpectedly shrunk window %u:%u (repaired)\n",
&np->daddr, ntohs(inet->dport),
inet->num, tp->snd_una, tp->snd_nxt);
}
#endif
#endif
if (tcp_time_stamp - tp->rcv_tstamp > TCP_RTO_MAX) {
tcp_write_err(sk);
goto out;
}
tcp_enter_loss(sk, 0);
tcp_retransmit_skb(sk, tcp_write_queue_head(sk));
__sk_dst_reset(sk);
goto out_reset_timer;
}
if (tcp_write_timeout(sk))
goto out;
if (icsk->icsk_retransmits == 0) {
int mib_idx;
if (icsk->icsk_ca_state == TCP_CA_Disorder) {
if (tcp_is_sack(tp))
mib_idx = LINUX_MIB_TCPSACKFAILURES;
else
mib_idx = LINUX_MIB_TCPRENOFAILURES;
} else if (icsk->icsk_ca_state == TCP_CA_Recovery) {
if (tcp_is_sack(tp))
mib_idx = LINUX_MIB_TCPSACKRECOVERYFAIL;
else
mib_idx = LINUX_MIB_TCPRENORECOVERYFAIL;
} else if (icsk->icsk_ca_state == TCP_CA_Loss) {
mib_idx = LINUX_MIB_TCPLOSSFAILURES;
} else {
mib_idx = LINUX_MIB_TCPTIMEOUTS;
}
NET_INC_STATS_BH(sock_net(sk), mib_idx);
}
if (tcp_use_frto(sk)) {
tcp_enter_frto(sk);
} else {
tcp_enter_loss(sk, 0);
}
if (tcp_retransmit_skb(sk, tcp_write_queue_head(sk)) > 0) {
/* Retransmission failed because of local congestion,
* do not backoff.
*/
if (!icsk->icsk_retransmits)
icsk->icsk_retransmits = 1;
inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
min(icsk->icsk_rto, TCP_RESOURCE_PROBE_INTERVAL),
TCP_RTO_MAX);
goto out;
}
/* Increase the timeout each time we retransmit. Note that
* we do not increase the rtt estimate. rto is initialized
* from rtt, but increases here. Jacobson (SIGCOMM 88) suggests
* that doubling rto each time is the least we can get away with.
* In KA9Q, Karn uses this for the first few times, and then
* goes to quadratic. netBSD doubles, but only goes up to *64,
* and clamps at 1 to 64 sec afterwards. Note that 120 sec is
* defined in the protocol as the maximum possible RTT. I guess
* we'll have to use something other than TCP to talk to the
* University of Mars.
*
* PAWS allows us longer timeouts and large windows, so once
* implemented ftp to mars will work nicely. We will have to fix
* the 120 second clamps though!
*/
icsk->icsk_backoff++;
icsk->icsk_retransmits++;
out_reset_timer:
icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX);
inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, icsk->icsk_rto, TCP_RTO_MAX);
if (retransmits_timed_out(sk, sysctl_tcp_retries1 + 1))
__sk_dst_reset(sk);
out:;
}
static void tcp_write_timer(unsigned long data)
{
struct sock *sk = (struct sock *)data;
struct inet_connection_sock *icsk = inet_csk(sk);
int event;
bh_lock_sock(sk);
if (sock_owned_by_user(sk)) {
/* Try again later */
sk_reset_timer(sk, &icsk->icsk_retransmit_timer, jiffies + (HZ / 20));
goto out_unlock;
}
if (sk->sk_state == TCP_CLOSE || !icsk->icsk_pending)
goto out;
if (time_after(icsk->icsk_timeout, jiffies)) {
sk_reset_timer(sk, &icsk->icsk_retransmit_timer, icsk->icsk_timeout);
goto out;
}
event = icsk->icsk_pending;
icsk->icsk_pending = 0;
switch (event) {
case ICSK_TIME_RETRANS:
tcp_retransmit_timer(sk);
break;
case ICSK_TIME_PROBE0:
tcp_probe_timer(sk);
break;
}
TCP_CHECK_TIMER(sk);
out:
sk_mem_reclaim(sk);
out_unlock:
bh_unlock_sock(sk);
sock_put(sk);
}
/*
* Timer for listening sockets
*/
static void tcp_synack_timer(struct sock *sk)
{
inet_csk_reqsk_queue_prune(sk, TCP_SYNQ_INTERVAL,
TCP_TIMEOUT_INIT, TCP_RTO_MAX);
}
void tcp_set_keepalive(struct sock *sk, int val)
{
if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN))
return;
if (val && !sock_flag(sk, SOCK_KEEPOPEN))
inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tcp_sk(sk)));
else if (!val)
inet_csk_delete_keepalive_timer(sk);
}
static void tcp_keepalive_timer (unsigned long data)
{
struct sock *sk = (struct sock *) data;
struct inet_connection_sock *icsk = inet_csk(sk);
struct tcp_sock *tp = tcp_sk(sk);
__u32 elapsed;
/* Only process if socket is not in use. */
bh_lock_sock(sk);
if (sock_owned_by_user(sk)) {
/* Try again later. */
inet_csk_reset_keepalive_timer (sk, HZ/20);
goto out;
}
if (sk->sk_state == TCP_LISTEN) {
tcp_synack_timer(sk);
goto out;
}
if (sk->sk_state == TCP_FIN_WAIT2 && sock_flag(sk, SOCK_DEAD)) {
if (tp->linger2 >= 0) {
const int tmo = tcp_fin_time(sk) - TCP_TIMEWAIT_LEN;
if (tmo > 0) {
tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
goto out;
}
}
tcp_send_active_reset(sk, GFP_ATOMIC);
goto death;
}
if (!sock_flag(sk, SOCK_KEEPOPEN) || sk->sk_state == TCP_CLOSE)
goto out;
elapsed = keepalive_time_when(tp);
/* It is alive without keepalive 8) */
if (tp->packets_out || tcp_send_head(sk))
goto resched;
elapsed = tcp_time_stamp - tp->rcv_tstamp;
if (elapsed >= keepalive_time_when(tp)) {
if (icsk->icsk_probes_out >= keepalive_probes(tp)) {
tcp_send_active_reset(sk, GFP_ATOMIC);
tcp_write_err(sk);
goto out;
}
if (tcp_write_wakeup(sk) <= 0) {
icsk->icsk_probes_out++;
elapsed = keepalive_intvl_when(tp);
} else {
/* If keepalive was lost due to local congestion,
* try harder.
*/
elapsed = TCP_RESOURCE_PROBE_INTERVAL;
}
} else {
/* It is tp->rcv_tstamp + keepalive_time_when(tp) */
elapsed = keepalive_time_when(tp) - elapsed;
}
TCP_CHECK_TIMER(sk);
sk_mem_reclaim(sk);
resched:
inet_csk_reset_keepalive_timer (sk, elapsed);
goto out;
death:
tcp_done(sk);
out:
bh_unlock_sock(sk);
sock_put(sk);
}