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![Alexander Duyck](/assets/img/avatar_default.png)
When setting congestion control via a BPF program it is seen that the
SYN/ACK for packets within a given flow will not include the ECT0 flag. A
bit of simple printk debugging shows that when this is configured without
BPF we will see the value INET_ECN_xmit value initialized in
tcp_assign_congestion_control however when we configure this via BPF the
socket is in the closed state and as such it isn't configured, and I do not
see it being initialized when we transition the socket into the listen
state. The result of this is that the ECT0 bit is configured based on
whatever the default state is for the socket.
Any easy way to reproduce this is to monitor the following with tcpdump:
tools/testing/selftests/bpf/test_progs -t bpf_tcp_ca
Without this patch the SYN/ACK will follow whatever the default is. If dctcp
all SYN/ACK packets will have the ECT0 bit set, and if it is not then ECT0
will be cleared on all SYN/ACK packets. With this patch applied the SYN/ACK
bit matches the value seen on the other packets in the given stream.
Fixes: 91b5b21c7c
("bpf: Add support for changing congestion control")
Signed-off-by: Alexander Duyck <alexanderduyck@fb.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
474 lines
12 KiB
C
474 lines
12 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* Pluggable TCP congestion control support and newReno
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* congestion control.
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* Based on ideas from I/O scheduler support and Web100.
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*
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* Copyright (C) 2005 Stephen Hemminger <shemminger@osdl.org>
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*/
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#define pr_fmt(fmt) "TCP: " fmt
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#include <linux/module.h>
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#include <linux/mm.h>
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#include <linux/types.h>
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#include <linux/list.h>
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#include <linux/gfp.h>
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#include <linux/jhash.h>
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#include <net/tcp.h>
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static DEFINE_SPINLOCK(tcp_cong_list_lock);
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static LIST_HEAD(tcp_cong_list);
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/* Simple linear search, don't expect many entries! */
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struct tcp_congestion_ops *tcp_ca_find(const char *name)
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{
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struct tcp_congestion_ops *e;
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list_for_each_entry_rcu(e, &tcp_cong_list, list) {
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if (strcmp(e->name, name) == 0)
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return e;
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}
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return NULL;
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}
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/* Must be called with rcu lock held */
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static struct tcp_congestion_ops *tcp_ca_find_autoload(struct net *net,
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const char *name)
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{
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struct tcp_congestion_ops *ca = tcp_ca_find(name);
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#ifdef CONFIG_MODULES
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if (!ca && capable(CAP_NET_ADMIN)) {
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rcu_read_unlock();
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request_module("tcp_%s", name);
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rcu_read_lock();
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ca = tcp_ca_find(name);
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}
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#endif
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return ca;
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}
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/* Simple linear search, not much in here. */
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struct tcp_congestion_ops *tcp_ca_find_key(u32 key)
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{
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struct tcp_congestion_ops *e;
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list_for_each_entry_rcu(e, &tcp_cong_list, list) {
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if (e->key == key)
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return e;
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}
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return NULL;
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}
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/*
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* Attach new congestion control algorithm to the list
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* of available options.
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*/
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int tcp_register_congestion_control(struct tcp_congestion_ops *ca)
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{
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int ret = 0;
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/* all algorithms must implement these */
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if (!ca->ssthresh || !ca->undo_cwnd ||
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!(ca->cong_avoid || ca->cong_control)) {
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pr_err("%s does not implement required ops\n", ca->name);
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return -EINVAL;
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}
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ca->key = jhash(ca->name, sizeof(ca->name), strlen(ca->name));
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spin_lock(&tcp_cong_list_lock);
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if (ca->key == TCP_CA_UNSPEC || tcp_ca_find_key(ca->key)) {
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pr_notice("%s already registered or non-unique key\n",
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ca->name);
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ret = -EEXIST;
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} else {
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list_add_tail_rcu(&ca->list, &tcp_cong_list);
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pr_debug("%s registered\n", ca->name);
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}
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spin_unlock(&tcp_cong_list_lock);
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return ret;
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}
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EXPORT_SYMBOL_GPL(tcp_register_congestion_control);
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/*
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* Remove congestion control algorithm, called from
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* the module's remove function. Module ref counts are used
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* to ensure that this can't be done till all sockets using
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* that method are closed.
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*/
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void tcp_unregister_congestion_control(struct tcp_congestion_ops *ca)
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{
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spin_lock(&tcp_cong_list_lock);
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list_del_rcu(&ca->list);
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spin_unlock(&tcp_cong_list_lock);
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/* Wait for outstanding readers to complete before the
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* module gets removed entirely.
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*
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* A try_module_get() should fail by now as our module is
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* in "going" state since no refs are held anymore and
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* module_exit() handler being called.
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*/
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synchronize_rcu();
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}
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EXPORT_SYMBOL_GPL(tcp_unregister_congestion_control);
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u32 tcp_ca_get_key_by_name(struct net *net, const char *name, bool *ecn_ca)
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{
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const struct tcp_congestion_ops *ca;
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u32 key = TCP_CA_UNSPEC;
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might_sleep();
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rcu_read_lock();
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ca = tcp_ca_find_autoload(net, name);
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if (ca) {
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key = ca->key;
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*ecn_ca = ca->flags & TCP_CONG_NEEDS_ECN;
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}
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rcu_read_unlock();
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return key;
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}
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EXPORT_SYMBOL_GPL(tcp_ca_get_key_by_name);
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char *tcp_ca_get_name_by_key(u32 key, char *buffer)
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{
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const struct tcp_congestion_ops *ca;
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char *ret = NULL;
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rcu_read_lock();
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ca = tcp_ca_find_key(key);
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if (ca)
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ret = strncpy(buffer, ca->name,
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TCP_CA_NAME_MAX);
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rcu_read_unlock();
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return ret;
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}
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EXPORT_SYMBOL_GPL(tcp_ca_get_name_by_key);
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/* Assign choice of congestion control. */
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void tcp_assign_congestion_control(struct sock *sk)
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{
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struct net *net = sock_net(sk);
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struct inet_connection_sock *icsk = inet_csk(sk);
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const struct tcp_congestion_ops *ca;
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rcu_read_lock();
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ca = rcu_dereference(net->ipv4.tcp_congestion_control);
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if (unlikely(!bpf_try_module_get(ca, ca->owner)))
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ca = &tcp_reno;
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icsk->icsk_ca_ops = ca;
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rcu_read_unlock();
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memset(icsk->icsk_ca_priv, 0, sizeof(icsk->icsk_ca_priv));
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if (ca->flags & TCP_CONG_NEEDS_ECN)
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INET_ECN_xmit(sk);
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else
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INET_ECN_dontxmit(sk);
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}
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void tcp_init_congestion_control(struct sock *sk)
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{
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struct inet_connection_sock *icsk = inet_csk(sk);
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tcp_sk(sk)->prior_ssthresh = 0;
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if (icsk->icsk_ca_ops->init)
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icsk->icsk_ca_ops->init(sk);
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if (tcp_ca_needs_ecn(sk))
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INET_ECN_xmit(sk);
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else
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INET_ECN_dontxmit(sk);
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icsk->icsk_ca_initialized = 1;
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}
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static void tcp_reinit_congestion_control(struct sock *sk,
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const struct tcp_congestion_ops *ca)
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{
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struct inet_connection_sock *icsk = inet_csk(sk);
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tcp_cleanup_congestion_control(sk);
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icsk->icsk_ca_ops = ca;
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icsk->icsk_ca_setsockopt = 1;
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memset(icsk->icsk_ca_priv, 0, sizeof(icsk->icsk_ca_priv));
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if (ca->flags & TCP_CONG_NEEDS_ECN)
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INET_ECN_xmit(sk);
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else
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INET_ECN_dontxmit(sk);
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if (!((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)))
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tcp_init_congestion_control(sk);
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}
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/* Manage refcounts on socket close. */
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void tcp_cleanup_congestion_control(struct sock *sk)
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{
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struct inet_connection_sock *icsk = inet_csk(sk);
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if (icsk->icsk_ca_ops->release)
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icsk->icsk_ca_ops->release(sk);
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bpf_module_put(icsk->icsk_ca_ops, icsk->icsk_ca_ops->owner);
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}
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/* Used by sysctl to change default congestion control */
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int tcp_set_default_congestion_control(struct net *net, const char *name)
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{
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struct tcp_congestion_ops *ca;
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const struct tcp_congestion_ops *prev;
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int ret;
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rcu_read_lock();
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ca = tcp_ca_find_autoload(net, name);
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if (!ca) {
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ret = -ENOENT;
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} else if (!bpf_try_module_get(ca, ca->owner)) {
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ret = -EBUSY;
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} else {
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prev = xchg(&net->ipv4.tcp_congestion_control, ca);
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if (prev)
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bpf_module_put(prev, prev->owner);
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ca->flags |= TCP_CONG_NON_RESTRICTED;
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ret = 0;
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}
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rcu_read_unlock();
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return ret;
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}
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/* Set default value from kernel configuration at bootup */
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static int __init tcp_congestion_default(void)
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{
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return tcp_set_default_congestion_control(&init_net,
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CONFIG_DEFAULT_TCP_CONG);
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}
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late_initcall(tcp_congestion_default);
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/* Build string with list of available congestion control values */
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void tcp_get_available_congestion_control(char *buf, size_t maxlen)
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{
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struct tcp_congestion_ops *ca;
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size_t offs = 0;
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rcu_read_lock();
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list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
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offs += snprintf(buf + offs, maxlen - offs,
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"%s%s",
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offs == 0 ? "" : " ", ca->name);
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if (WARN_ON_ONCE(offs >= maxlen))
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break;
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}
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rcu_read_unlock();
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}
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/* Get current default congestion control */
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void tcp_get_default_congestion_control(struct net *net, char *name)
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{
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const struct tcp_congestion_ops *ca;
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rcu_read_lock();
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ca = rcu_dereference(net->ipv4.tcp_congestion_control);
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strncpy(name, ca->name, TCP_CA_NAME_MAX);
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rcu_read_unlock();
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}
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/* Built list of non-restricted congestion control values */
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void tcp_get_allowed_congestion_control(char *buf, size_t maxlen)
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{
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struct tcp_congestion_ops *ca;
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size_t offs = 0;
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*buf = '\0';
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rcu_read_lock();
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list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
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if (!(ca->flags & TCP_CONG_NON_RESTRICTED))
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continue;
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offs += snprintf(buf + offs, maxlen - offs,
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"%s%s",
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offs == 0 ? "" : " ", ca->name);
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if (WARN_ON_ONCE(offs >= maxlen))
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break;
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}
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rcu_read_unlock();
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}
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/* Change list of non-restricted congestion control */
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int tcp_set_allowed_congestion_control(char *val)
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{
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struct tcp_congestion_ops *ca;
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char *saved_clone, *clone, *name;
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int ret = 0;
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saved_clone = clone = kstrdup(val, GFP_USER);
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if (!clone)
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return -ENOMEM;
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spin_lock(&tcp_cong_list_lock);
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/* pass 1 check for bad entries */
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while ((name = strsep(&clone, " ")) && *name) {
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ca = tcp_ca_find(name);
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if (!ca) {
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ret = -ENOENT;
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goto out;
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}
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}
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/* pass 2 clear old values */
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list_for_each_entry_rcu(ca, &tcp_cong_list, list)
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ca->flags &= ~TCP_CONG_NON_RESTRICTED;
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/* pass 3 mark as allowed */
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while ((name = strsep(&val, " ")) && *name) {
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ca = tcp_ca_find(name);
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WARN_ON(!ca);
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if (ca)
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ca->flags |= TCP_CONG_NON_RESTRICTED;
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}
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out:
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spin_unlock(&tcp_cong_list_lock);
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kfree(saved_clone);
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return ret;
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}
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/* Change congestion control for socket. If load is false, then it is the
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* responsibility of the caller to call tcp_init_congestion_control or
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* tcp_reinit_congestion_control (if the current congestion control was
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* already initialized.
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*/
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int tcp_set_congestion_control(struct sock *sk, const char *name, bool load,
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bool cap_net_admin)
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{
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struct inet_connection_sock *icsk = inet_csk(sk);
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const struct tcp_congestion_ops *ca;
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int err = 0;
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if (icsk->icsk_ca_dst_locked)
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return -EPERM;
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rcu_read_lock();
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if (!load)
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ca = tcp_ca_find(name);
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else
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ca = tcp_ca_find_autoload(sock_net(sk), name);
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/* No change asking for existing value */
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if (ca == icsk->icsk_ca_ops) {
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icsk->icsk_ca_setsockopt = 1;
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goto out;
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}
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if (!ca)
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err = -ENOENT;
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else if (!((ca->flags & TCP_CONG_NON_RESTRICTED) || cap_net_admin))
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err = -EPERM;
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else if (!bpf_try_module_get(ca, ca->owner))
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err = -EBUSY;
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else
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tcp_reinit_congestion_control(sk, ca);
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out:
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rcu_read_unlock();
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return err;
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}
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/* Slow start is used when congestion window is no greater than the slow start
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* threshold. We base on RFC2581 and also handle stretch ACKs properly.
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* We do not implement RFC3465 Appropriate Byte Counting (ABC) per se but
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* something better;) a packet is only considered (s)acked in its entirety to
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* defend the ACK attacks described in the RFC. Slow start processes a stretch
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* ACK of degree N as if N acks of degree 1 are received back to back except
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* ABC caps N to 2. Slow start exits when cwnd grows over ssthresh and
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* returns the leftover acks to adjust cwnd in congestion avoidance mode.
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*/
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u32 tcp_slow_start(struct tcp_sock *tp, u32 acked)
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{
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u32 cwnd = min(tp->snd_cwnd + acked, tp->snd_ssthresh);
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acked -= cwnd - tp->snd_cwnd;
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tp->snd_cwnd = min(cwnd, tp->snd_cwnd_clamp);
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return acked;
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}
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EXPORT_SYMBOL_GPL(tcp_slow_start);
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/* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd (or alternative w),
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* for every packet that was ACKed.
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*/
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void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w, u32 acked)
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{
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/* If credits accumulated at a higher w, apply them gently now. */
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if (tp->snd_cwnd_cnt >= w) {
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tp->snd_cwnd_cnt = 0;
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tp->snd_cwnd++;
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}
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tp->snd_cwnd_cnt += acked;
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if (tp->snd_cwnd_cnt >= w) {
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u32 delta = tp->snd_cwnd_cnt / w;
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tp->snd_cwnd_cnt -= delta * w;
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tp->snd_cwnd += delta;
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}
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tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_cwnd_clamp);
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}
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EXPORT_SYMBOL_GPL(tcp_cong_avoid_ai);
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/*
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* TCP Reno congestion control
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* This is special case used for fallback as well.
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*/
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/* This is Jacobson's slow start and congestion avoidance.
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* SIGCOMM '88, p. 328.
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*/
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void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 acked)
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{
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struct tcp_sock *tp = tcp_sk(sk);
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if (!tcp_is_cwnd_limited(sk))
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return;
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/* In "safe" area, increase. */
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if (tcp_in_slow_start(tp)) {
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acked = tcp_slow_start(tp, acked);
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if (!acked)
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return;
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}
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/* In dangerous area, increase slowly. */
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tcp_cong_avoid_ai(tp, tp->snd_cwnd, acked);
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}
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EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);
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/* Slow start threshold is half the congestion window (min 2) */
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u32 tcp_reno_ssthresh(struct sock *sk)
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{
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const struct tcp_sock *tp = tcp_sk(sk);
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return max(tp->snd_cwnd >> 1U, 2U);
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}
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EXPORT_SYMBOL_GPL(tcp_reno_ssthresh);
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u32 tcp_reno_undo_cwnd(struct sock *sk)
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{
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const struct tcp_sock *tp = tcp_sk(sk);
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return max(tp->snd_cwnd, tp->prior_cwnd);
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}
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EXPORT_SYMBOL_GPL(tcp_reno_undo_cwnd);
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struct tcp_congestion_ops tcp_reno = {
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.flags = TCP_CONG_NON_RESTRICTED,
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.name = "reno",
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.owner = THIS_MODULE,
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.ssthresh = tcp_reno_ssthresh,
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.cong_avoid = tcp_reno_cong_avoid,
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.undo_cwnd = tcp_reno_undo_cwnd,
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};
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