1 files changed, 294 insertions, 163 deletions

diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c
index 019c2389a341..df758adbb445 100644
--- a/net/ipv4/tcp_cong.c
+++ b/net/ipv4/tcp_cong.c
@@ -1,5 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0-only
 /*
- * Plugable TCP congestion control support and newReno
+ * Pluggable TCP congestion control support and newReno
  * congestion control.
  * Based on ideas from I/O scheduler support and Web100.
  *
@@ -13,15 +14,15 @@
 #include <linux/types.h>
 #include <linux/list.h>
 #include <linux/gfp.h>
+#include <linux/jhash.h>
 #include <net/tcp.h>
-
-int sysctl_tcp_max_ssthresh = 0;
+#include <trace/events/tcp.h>
 
 static DEFINE_SPINLOCK(tcp_cong_list_lock);
 static LIST_HEAD(tcp_cong_list);
 
 /* Simple linear search, don't expect many entries! */
-static struct tcp_congestion_ops *tcp_ca_find(const char *name)
+struct tcp_congestion_ops *tcp_ca_find(const char *name)
 {
 	struct tcp_congestion_ops *e;
 
@@ -33,27 +34,79 @@ static struct tcp_congestion_ops *tcp_ca_find(const char *name)
 	return NULL;
 }
 
-/*
- * Attach new congestion control algorithm to the list
- * of available options.
- */
-int tcp_register_congestion_control(struct tcp_congestion_ops *ca)
+void tcp_set_ca_state(struct sock *sk, const u8 ca_state)
 {
-	int ret = 0;
+	struct inet_connection_sock *icsk = inet_csk(sk);
+
+	trace_tcp_cong_state_set(sk, ca_state);
 
-	/* all algorithms must implement ssthresh and cong_avoid ops */
-	if (!ca->ssthresh || !ca->cong_avoid) {
+	if (icsk->icsk_ca_ops->set_state)
+		icsk->icsk_ca_ops->set_state(sk, ca_state);
+	icsk->icsk_ca_state = ca_state;
+}
+
+/* Must be called with rcu lock held */
+static struct tcp_congestion_ops *tcp_ca_find_autoload(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;
+}
+
+int tcp_validate_congestion_control(struct tcp_congestion_ops *ca)
+{
+	/* 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;
 	}
 
+	return 0;
+}
+
+/* Attach new congestion control algorithm to the list
+ * of available options.
+ */
+int tcp_register_congestion_control(struct tcp_congestion_ops *ca)
+{
+	int ret;
+
+	ret = tcp_validate_congestion_control(ca);
+	if (ret)
+		return ret;
+
+	ca->key = jhash(ca->name, sizeof(ca->name), strlen(ca->name));
+
 	spin_lock(&tcp_cong_list_lock);
-	if (tcp_ca_find(ca->name)) {
-		pr_notice("%s already registered\n", ca->name);
+	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_info("%s registered\n", ca->name);
+		pr_debug("%s registered\n", ca->name);
 	}
 	spin_unlock(&tcp_cong_list_lock);
 
@@ -72,31 +125,144 @@ 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);
 
+/* Replace a registered old ca with a new one.
+ *
+ * The new ca must have the same name as the old one, that has been
+ * registered.
+ */
+int tcp_update_congestion_control(struct tcp_congestion_ops *ca, struct tcp_congestion_ops *old_ca)
+{
+	struct tcp_congestion_ops *existing;
+	int ret = 0;
+
+	ca->key = jhash(ca->name, sizeof(ca->name), strlen(ca->name));
+
+	spin_lock(&tcp_cong_list_lock);
+	existing = tcp_ca_find_key(old_ca->key);
+	if (ca->key == TCP_CA_UNSPEC || !existing || strcmp(existing->name, ca->name)) {
+		pr_notice("%s not registered or non-unique key\n",
+			  ca->name);
+		ret = -EINVAL;
+	} else if (existing != old_ca) {
+		pr_notice("invalid old congestion control algorithm to replace\n");
+		ret = -EINVAL;
+	} else {
+		/* Add the new one before removing the old one to keep
+		 * one implementation available all the time.
+		 */
+		list_add_tail_rcu(&ca->list, &tcp_cong_list);
+		list_del_rcu(&existing->list);
+		pr_debug("%s updated\n", ca->name);
+	}
+	spin_unlock(&tcp_cong_list_lock);
+
+	/* Wait for outstanding readers to complete before the
+	 * module or struct_ops gets removed entirely.
+	 */
+	if (!ret)
+		synchronize_rcu();
+
+	return ret;
+}
+
+u32 tcp_ca_get_key_by_name(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(name);
+	if (ca) {
+		key = ca->key;
+		*ecn_ca = ca->flags & TCP_CONG_NEEDS_ECN;
+	}
+	rcu_read_unlock();
+
+	return key;
+}
+
+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) {
+		strscpy(buffer, ca->name, TCP_CA_NAME_MAX);
+		ret = buffer;
+	}
+	rcu_read_unlock();
+
+	return ret;
+}
+
 /* Assign choice of congestion control. */
-void tcp_init_congestion_control(struct sock *sk)
+void tcp_assign_congestion_control(struct sock *sk)
 {
+	struct net *net = sock_net(sk);
 	struct inet_connection_sock *icsk = inet_csk(sk);
-	struct tcp_congestion_ops *ca;
+	const struct tcp_congestion_ops *ca;
 
-	/* if no choice made yet assign the current value set as default */
-	if (icsk->icsk_ca_ops == &tcp_init_congestion_ops) {
-		rcu_read_lock();
-		list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
-			if (try_module_get(ca->owner)) {
-				icsk->icsk_ca_ops = ca;
-				break;
-			}
+	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();
 
-			/* fallback to next available */
-		}
-		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 (ca->flags & TCP_CONG_NEEDS_ECN)
+		INET_ECN_xmit(sk);
+	else
+		INET_ECN_dontxmit(sk);
+
+	if (!((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)))
+		tcp_init_congestion_control(sk);
 }
 
 /* Manage refcounts on socket close. */
@@ -104,35 +270,38 @@ void tcp_cleanup_congestion_control(struct sock *sk)
 {
 	struct inet_connection_sock *icsk = inet_csk(sk);
 
-	if (icsk->icsk_ca_ops->release)
+	if (icsk->icsk_ca_initialized && icsk->icsk_ca_ops->release)
 		icsk->icsk_ca_ops->release(sk);
-	module_put(icsk->icsk_ca_ops->owner);
+	icsk->icsk_ca_initialized = 0;
+	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(const char *name)
+int tcp_set_default_congestion_control(struct net *net, const char *name)
 {
 	struct tcp_congestion_ops *ca;
-	int ret = -ENOENT;
+	const struct tcp_congestion_ops *prev;
+	int ret;
 
-	spin_lock(&tcp_cong_list_lock);
-	ca = tcp_ca_find(name);
-#ifdef CONFIG_MODULES
-	if (!ca && capable(CAP_NET_ADMIN)) {
-		spin_unlock(&tcp_cong_list_lock);
-
-		request_module("tcp_%s", name);
-		spin_lock(&tcp_cong_list_lock);
-		ca = tcp_ca_find(name);
-	}
-#endif
+	rcu_read_lock();
+	ca = tcp_ca_find_autoload(name);
+	if (!ca) {
+		ret = -ENOENT;
+	} else if (!bpf_try_module_get(ca, ca->owner)) {
+		ret = -EBUSY;
+	} else if (!net_eq(net, &init_net) &&
+			!(ca->flags & TCP_CONG_NON_RESTRICTED)) {
+		/* Only init netns can set default to a restricted algorithm */
+		ret = -EPERM;
+	} else {
+		prev = xchg(&net->ipv4.tcp_congestion_control, ca);
+		if (prev)
+			bpf_module_put(prev, prev->owner);
 
-	if (ca) {
-		ca->flags |= TCP_CONG_NON_RESTRICTED;	/* default is always allowed */
-		list_move(&ca->list, &tcp_cong_list);
+		ca->flags |= TCP_CONG_NON_RESTRICTED;
 		ret = 0;
 	}
-	spin_unlock(&tcp_cong_list_lock);
+	rcu_read_unlock();
 
 	return ret;
 }
@@ -140,11 +309,11 @@ int tcp_set_default_congestion_control(const char *name)
 /* Set default value from kernel configuration at bootup */
 static int __init tcp_congestion_default(void)
 {
-	return tcp_set_default_congestion_control(CONFIG_DEFAULT_TCP_CONG);
+	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)
 {
@@ -157,20 +326,20 @@ void tcp_get_available_congestion_control(char *buf, size_t maxlen)
 				 "%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(char *name)
+void tcp_get_default_congestion_control(struct net *net, char *name)
 {
-	struct tcp_congestion_ops *ca;
-	/* We will always have reno... */
-	BUG_ON(list_empty(&tcp_cong_list));
+	const struct tcp_congestion_ops *ca;
 
 	rcu_read_lock();
-	ca = list_entry(tcp_cong_list.next, struct tcp_congestion_ops, list);
-	strncpy(name, ca->name, TCP_CA_NAME_MAX);
+	ca = rcu_dereference(net->ipv4.tcp_congestion_control);
+	strscpy(name, ca->name, TCP_CA_NAME_MAX);
 	rcu_read_unlock();
 }
 
@@ -189,6 +358,8 @@ void tcp_get_allowed_congestion_control(char *buf, size_t maxlen)
 				 "%s%s",
 				 offs == 0 ? "" : " ", ca->name);
 
+		if (WARN_ON_ONCE(offs >= maxlen))
+			break;
 	}
 	rcu_read_unlock();
 }
@@ -232,115 +403,85 @@ out:
 	return ret;
 }
 
-
-/* Change congestion control for socket */
-int tcp_set_congestion_control(struct sock *sk, const char *name)
+/* 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);
-	struct tcp_congestion_ops *ca;
+	const struct tcp_congestion_ops *ca;
 	int err = 0;
 
+	if (icsk->icsk_ca_dst_locked)
+		return -EPERM;
+
 	rcu_read_lock();
-	ca = tcp_ca_find(name);
+	if (!load)
+		ca = tcp_ca_find(name);
+	else
+		ca = tcp_ca_find_autoload(name);
 
-	/* no change asking for existing value */
-	if (ca == icsk->icsk_ca_ops)
+	/* No change asking for existing value */
+	if (ca == icsk->icsk_ca_ops) {
+		icsk->icsk_ca_setsockopt = 1;
 		goto out;
-
-#ifdef CONFIG_MODULES
-	/* not found attempt to autoload module */
-	if (!ca && capable(CAP_NET_ADMIN)) {
-		rcu_read_unlock();
-		request_module("tcp_%s", name);
-		rcu_read_lock();
-		ca = tcp_ca_find(name);
 	}
-#endif
+
 	if (!ca)
 		err = -ENOENT;
-
-	else if (!((ca->flags & TCP_CONG_NON_RESTRICTED) ||
-		   ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN)))
+	else if (!((ca->flags & TCP_CONG_NON_RESTRICTED) || cap_net_admin))
 		err = -EPERM;
-
-	else if (!try_module_get(ca->owner))
+	else if (!bpf_try_module_get(ca, ca->owner))
 		err = -EBUSY;
-
-	else {
-		tcp_cleanup_congestion_control(sk);
-		icsk->icsk_ca_ops = ca;
-
-		if (sk->sk_state != TCP_CLOSE && icsk->icsk_ca_ops->init)
-			icsk->icsk_ca_ops->init(sk);
-	}
+	else
+		tcp_reinit_congestion_control(sk, ca);
  out:
 	rcu_read_unlock();
 	return err;
 }
 
-/* RFC2861 Check whether we are limited by application or congestion window
- * This is the inverse of cwnd check in tcp_tso_should_defer
+/* 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.
  */
-bool tcp_is_cwnd_limited(const struct sock *sk, u32 in_flight)
+__bpf_kfunc u32 tcp_slow_start(struct tcp_sock *tp, u32 acked)
 {
-	const struct tcp_sock *tp = tcp_sk(sk);
-	u32 left;
-
-	if (in_flight >= tp->snd_cwnd)
-		return true;
-
-	left = tp->snd_cwnd - in_flight;
-	if (sk_can_gso(sk) &&
-	    left * sysctl_tcp_tso_win_divisor < tp->snd_cwnd &&
-	    left * tp->mss_cache < sk->sk_gso_max_size &&
-	    left < sk->sk_gso_max_segs)
-		return true;
-	return left <= tcp_max_tso_deferred_mss(tp);
-}
-EXPORT_SYMBOL_GPL(tcp_is_cwnd_limited);
+	u32 cwnd = min(tcp_snd_cwnd(tp) + acked, tp->snd_ssthresh);
 
-/*
- * Slow start is used when congestion window is less than slow start
- * threshold. This version implements the basic RFC2581 version
- * and optionally supports:
- * 	RFC3742 Limited Slow Start  	  - growth limited to max_ssthresh
- *	RFC3465 Appropriate Byte Counting - growth limited by bytes acknowledged
- */
-void tcp_slow_start(struct tcp_sock *tp)
-{
-	int cnt; /* increase in packets */
-	unsigned int delta = 0;
-	u32 snd_cwnd = tp->snd_cwnd;
+	acked -= cwnd - tcp_snd_cwnd(tp);
+	tcp_snd_cwnd_set(tp, min(cwnd, tp->snd_cwnd_clamp));
 
-	if (unlikely(!snd_cwnd)) {
-		pr_err_once("snd_cwnd is nul, please report this bug.\n");
-		snd_cwnd = 1U;
-	}
-
-	if (sysctl_tcp_max_ssthresh > 0 && tp->snd_cwnd > sysctl_tcp_max_ssthresh)
-		cnt = sysctl_tcp_max_ssthresh >> 1;	/* limited slow start */
-	else
-		cnt = snd_cwnd;				/* exponential increase */
-
-	tp->snd_cwnd_cnt += cnt;
-	while (tp->snd_cwnd_cnt >= snd_cwnd) {
-		tp->snd_cwnd_cnt -= snd_cwnd;
-		delta++;
-	}
-	tp->snd_cwnd = min(snd_cwnd + delta, 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) */
-void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w)
+/* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd (or alternative w),
+ * for every packet that was ACKed.
+ */
+__bpf_kfunc 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) {
-		if (tp->snd_cwnd < tp->snd_cwnd_clamp)
-			tp->snd_cwnd++;
 		tp->snd_cwnd_cnt = 0;
-	} else {
-		tp->snd_cwnd_cnt++;
+		tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) + 1);
+	}
+
+	tp->snd_cwnd_cnt += acked;
+	if (tp->snd_cwnd_cnt >= w) {
+		u32 delta = tp->snd_cwnd_cnt / w;
+
+		tp->snd_cwnd_cnt -= delta * w;
+		tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) + delta);
 	}
+	tcp_snd_cwnd_set(tp, min(tcp_snd_cwnd(tp), tp->snd_cwnd_clamp));
 }
 EXPORT_SYMBOL_GPL(tcp_cong_avoid_ai);
 
@@ -351,37 +492,40 @@ EXPORT_SYMBOL_GPL(tcp_cong_avoid_ai);
 /* This is Jacobson's slow start and congestion avoidance.
  * SIGCOMM '88, p. 328.
  */
-void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
+__bpf_kfunc 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, in_flight))
+	if (!tcp_is_cwnd_limited(sk))
 		return;
 
 	/* In "safe" area, increase. */
-	if (tp->snd_cwnd <= tp->snd_ssthresh)
-		tcp_slow_start(tp);
+	if (tcp_in_slow_start(tp)) {
+		acked = tcp_slow_start(tp, acked);
+		if (!acked)
+			return;
+	}
 	/* In dangerous area, increase slowly. */
-	else
-		tcp_cong_avoid_ai(tp, tp->snd_cwnd);
+	tcp_cong_avoid_ai(tp, tcp_snd_cwnd(tp), 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)
+__bpf_kfunc u32 tcp_reno_ssthresh(struct sock *sk)
 {
 	const struct tcp_sock *tp = tcp_sk(sk);
-	return max(tp->snd_cwnd >> 1U, 2U);
+
+	return max(tcp_snd_cwnd(tp) >> 1U, 2U);
 }
 EXPORT_SYMBOL_GPL(tcp_reno_ssthresh);
 
-/* Lower bound on congestion window with halving. */
-u32 tcp_reno_min_cwnd(const struct sock *sk)
+__bpf_kfunc u32 tcp_reno_undo_cwnd(struct sock *sk)
 {
 	const struct tcp_sock *tp = tcp_sk(sk);
-	return tp->snd_ssthresh/2;
+
+	return max(tcp_snd_cwnd(tp), tp->prior_cwnd);
 }
-EXPORT_SYMBOL_GPL(tcp_reno_min_cwnd);
+EXPORT_SYMBOL_GPL(tcp_reno_undo_cwnd);
 
 struct tcp_congestion_ops tcp_reno = {
 	.flags		= TCP_CONG_NON_RESTRICTED,
@@ -389,18 +533,5 @@ struct tcp_congestion_ops tcp_reno = {
 	.owner		= THIS_MODULE,
 	.ssthresh	= tcp_reno_ssthresh,
 	.cong_avoid	= tcp_reno_cong_avoid,
-	.min_cwnd	= tcp_reno_min_cwnd,
-};
-
-/* Initial congestion control used (until SYN)
- * really reno under another name so we can tell difference
- * during tcp_set_default_congestion_control
- */
-struct tcp_congestion_ops tcp_init_congestion_ops  = {
-	.name		= "",
-	.owner		= THIS_MODULE,
-	.ssthresh	= tcp_reno_ssthresh,
-	.cong_avoid	= tcp_reno_cong_avoid,
-	.min_cwnd	= tcp_reno_min_cwnd,
+	.undo_cwnd	= tcp_reno_undo_cwnd,
 };
-EXPORT_SYMBOL_GPL(tcp_init_congestion_ops);