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