ftrace: Synchronize the initialization of ftrace_opsgrafted

There's some internal state that ftrace_ops needs to have set, but since
it can be declared outside of the ftrace.c code, it calls
ftrace_ops_init() on the ops in every global function. The issue is that
if two tasks call it on the same ops at the same time it is possible to
have the initialization of one corrupt the initialization of the other
call.

Create a ops_mutex to use to synchronize every initialization of the
ftrace_ops. The mutex is taken within checking the ftrace_ops flag that
states it was initializied but the flag is checked again after the mutex
has been taken. Checking first outside the mutex allows it to shortcut
having to take the mutex. But then the check needs to be done again after
the mute is taken in case of races.

Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260902095501.6b59af20@gandalf.local.home
Fixes: f04f24fb7e48d ("ftrace, kprobes: Fix a deadlock on ftrace_regex_lock")
Reported-by: sashiko-bot@kernel.org
Close: https://lore.kernel.org/all/20260829025528.49A831F000E9@smtp.kernel.org/
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 319 insertions, 0 deletions

diff --git a/net/ipv4/tcp_dctcp.c b/net/ipv4/tcp_dctcp.c
new file mode 100644
index 000000000..274e628e7
--- /dev/null
+++ b/net/ipv4/tcp_dctcp.c
@@ -0,0 +1,319 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* DataCenter TCP (DCTCP) congestion control.
+ *
+ * http://simula.stanford.edu/~alizade/Site/DCTCP.html
+ *
+ * This is an implementation of DCTCP over Reno, an enhancement to the
+ * TCP congestion control algorithm designed for data centers. DCTCP
+ * leverages Explicit Congestion Notification (ECN) in the network to
+ * provide multi-bit feedback to the end hosts. DCTCP's goal is to meet
+ * the following three data center transport requirements:
+ *
+ *  - High burst tolerance (incast due to partition/aggregate)
+ *  - Low latency (short flows, queries)
+ *  - High throughput (continuous data updates, large file transfers)
+ *    with commodity shallow buffered switches
+ *
+ * The algorithm is described in detail in the following two papers:
+ *
+ * 1) Mohammad Alizadeh, Albert Greenberg, David A. Maltz, Jitendra Padhye,
+ *    Parveen Patel, Balaji Prabhakar, Sudipta Sengupta, and Murari Sridharan:
+ *      "Data Center TCP (DCTCP)", Data Center Networks session
+ *      Proc. ACM SIGCOMM, New Delhi, 2010.
+ *   http://simula.stanford.edu/~alizade/Site/DCTCP_files/dctcp-final.pdf
+ *
+ * 2) Mohammad Alizadeh, Adel Javanmard, and Balaji Prabhakar:
+ *      "Analysis of DCTCP: Stability, Convergence, and Fairness"
+ *      Proc. ACM SIGMETRICS, San Jose, 2011.
+ *   http://simula.stanford.edu/~alizade/Site/DCTCP_files/dctcp_analysis-full.pdf
+ *
+ * Initial prototype from Abdul Kabbani, Masato Yasuda and Mohammad Alizadeh.
+ *
+ * Authors:
+ *
+ *	Daniel Borkmann <dborkman@redhat.com>
+ *	Florian Westphal <fw@strlen.de>
+ *	Glenn Judd <glenn.judd@morganstanley.com>
+ */
+
+#include <linux/btf.h>
+#include <linux/btf_ids.h>
+#include <linux/module.h>
+#include <linux/mm.h>
+#include <net/tcp.h>
+#include <linux/inet_diag.h>
+#include "tcp_dctcp.h"
+
+#define DCTCP_MAX_ALPHA	1024U
+
+struct dctcp {
+	u32 old_delivered;
+	u32 old_delivered_ce;
+	u32 prior_rcv_nxt;
+	u32 dctcp_alpha;
+	u32 next_seq;
+	u32 ce_state;
+	u32 loss_cwnd;
+	struct tcp_plb_state plb;
+};
+
+static unsigned int dctcp_shift_g __read_mostly = 4; /* g = 1/2^4 */
+
+static int dctcp_shift_g_set(const char *val, const struct kernel_param *kp)
+{
+	return param_set_uint_minmax(val, kp, 0, 10);
+}
+
+static const struct kernel_param_ops dctcp_shift_g_ops = {
+	.set = dctcp_shift_g_set,
+	.get = param_get_uint,
+};
+
+module_param_cb(dctcp_shift_g, &dctcp_shift_g_ops, &dctcp_shift_g, 0644);
+MODULE_PARM_DESC(dctcp_shift_g, "parameter g for updating dctcp_alpha");
+
+static unsigned int dctcp_alpha_on_init __read_mostly = DCTCP_MAX_ALPHA;
+module_param(dctcp_alpha_on_init, uint, 0644);
+MODULE_PARM_DESC(dctcp_alpha_on_init, "parameter for initial alpha value");
+
+static struct tcp_congestion_ops dctcp_reno;
+
+static void dctcp_reset(const struct tcp_sock *tp, struct dctcp *ca)
+{
+	ca->next_seq = tp->snd_nxt;
+
+	ca->old_delivered = tp->delivered;
+	ca->old_delivered_ce = tp->delivered_ce;
+}
+
+__bpf_kfunc static void dctcp_init(struct sock *sk)
+{
+	const struct tcp_sock *tp = tcp_sk(sk);
+
+	if (tcp_ecn_mode_any(tp) ||
+	    (sk->sk_state == TCP_LISTEN ||
+	     sk->sk_state == TCP_CLOSE)) {
+		struct dctcp *ca = inet_csk_ca(sk);
+
+		ca->prior_rcv_nxt = tp->rcv_nxt;
+
+		ca->dctcp_alpha = min(dctcp_alpha_on_init, DCTCP_MAX_ALPHA);
+
+		ca->loss_cwnd = 0;
+		ca->ce_state = 0;
+
+		dctcp_reset(tp, ca);
+		tcp_plb_init(sk, &ca->plb);
+
+		return;
+	}
+
+	/* No ECN support? Fall back to Reno. Also need to clear
+	 * ECT from sk since it is set during 3WHS for DCTCP.
+	 */
+	inet_csk(sk)->icsk_ca_ops = &dctcp_reno;
+	INET_ECN_dontxmit(sk);
+}
+
+__bpf_kfunc static u32 dctcp_ssthresh(struct sock *sk)
+{
+	struct dctcp *ca = inet_csk_ca(sk);
+	struct tcp_sock *tp = tcp_sk(sk);
+
+	ca->loss_cwnd = tcp_snd_cwnd(tp);
+	return max(tcp_snd_cwnd(tp) - ((tcp_snd_cwnd(tp) * ca->dctcp_alpha) >> 11U), 2U);
+}
+
+__bpf_kfunc static void dctcp_update_alpha(struct sock *sk, u32 flags)
+{
+	const struct tcp_sock *tp = tcp_sk(sk);
+	struct dctcp *ca = inet_csk_ca(sk);
+
+	/* Expired RTT */
+	if (!before(tp->snd_una, ca->next_seq)) {
+		u32 delivered = tp->delivered - ca->old_delivered;
+		u32 delivered_ce = tp->delivered_ce - ca->old_delivered_ce;
+		u32 alpha = ca->dctcp_alpha;
+		u32 ce_ratio = 0;
+
+		if (delivered > 0) {
+			/* dctcp_alpha keeps EWMA of fraction of ECN marked
+			 * packets. Because of EWMA smoothing, PLB reaction can
+			 * be slow so we use ce_ratio which is an instantaneous
+			 * measure of congestion. ce_ratio is the fraction of
+			 * ECN marked packets in the previous RTT.
+			 */
+			if (delivered_ce > 0)
+				ce_ratio = (delivered_ce << TCP_PLB_SCALE) / delivered;
+			tcp_plb_update_state(sk, &ca->plb, (int)ce_ratio);
+			tcp_plb_check_rehash(sk, &ca->plb);
+		}
+
+		/* alpha = (1 - g) * alpha + g * F */
+
+		alpha -= min_not_zero(alpha, alpha >> dctcp_shift_g);
+		if (delivered_ce) {
+
+			/* If dctcp_shift_g == 1, a 32bit value would overflow
+			 * after 8 M packets.
+			 */
+			delivered_ce <<= (10 - dctcp_shift_g);
+			delivered_ce /= max(1U, delivered);
+
+			alpha = min(alpha + delivered_ce, DCTCP_MAX_ALPHA);
+		}
+		/* dctcp_alpha can be read from dctcp_get_info() without
+		 * synchro, so we ask compiler to not use dctcp_alpha
+		 * as a temporary variable in prior operations.
+		 */
+		WRITE_ONCE(ca->dctcp_alpha, alpha);
+		dctcp_reset(tp, ca);
+	}
+}
+
+static void dctcp_react_to_loss(struct sock *sk)
+{
+	struct dctcp *ca = inet_csk_ca(sk);
+	struct tcp_sock *tp = tcp_sk(sk);
+
+	ca->loss_cwnd = tcp_snd_cwnd(tp);
+	WRITE_ONCE(tp->snd_ssthresh, max(tcp_snd_cwnd(tp) >> 1U, 2U));
+}
+
+__bpf_kfunc static void dctcp_state(struct sock *sk, u8 new_state)
+{
+	if (new_state == TCP_CA_Recovery &&
+	    new_state != inet_csk(sk)->icsk_ca_state)
+		dctcp_react_to_loss(sk);
+	/* We handle RTO in dctcp_cwnd_event to ensure that we perform only
+	 * one loss-adjustment per RTT.
+	 */
+}
+
+__bpf_kfunc static void dctcp_cwnd_event(struct sock *sk, enum tcp_ca_event ev)
+{
+	struct dctcp *ca = inet_csk_ca(sk);
+
+	switch (ev) {
+	case CA_EVENT_ECN_IS_CE:
+	case CA_EVENT_ECN_NO_CE:
+		dctcp_ece_ack_update(sk, ev, &ca->prior_rcv_nxt, &ca->ce_state);
+		break;
+	case CA_EVENT_LOSS:
+		tcp_plb_update_state_upon_rto(sk, &ca->plb);
+		dctcp_react_to_loss(sk);
+		break;
+	default:
+		/* Don't care for the rest. */
+		break;
+	}
+}
+
+__bpf_kfunc static void dctcp_cwnd_event_tx_start(struct sock *sk)
+{
+	struct dctcp *ca = inet_csk_ca(sk);
+
+	tcp_plb_check_rehash(sk, &ca->plb); /* Maybe rehash when inflight is 0 */
+}
+
+static size_t dctcp_get_info(struct sock *sk, u32 ext, int *attr,
+			     union tcp_cc_info *info)
+{
+	const struct dctcp *ca = inet_csk_ca(sk);
+	const struct tcp_sock *tp = tcp_sk(sk);
+
+	/* Fill it also in case of VEGASINFO due to req struct limits.
+	 * We can still correctly retrieve it later.
+	 */
+	if (ext & (1 << (INET_DIAG_DCTCPINFO - 1)) ||
+	    ext & (1 << (INET_DIAG_VEGASINFO - 1))) {
+		memset(&info->dctcp, 0, sizeof(info->dctcp));
+		if (inet_csk(sk)->icsk_ca_ops != &dctcp_reno) {
+			info->dctcp.dctcp_enabled = 1;
+			info->dctcp.dctcp_ce_state = (u16) ca->ce_state;
+			info->dctcp.dctcp_alpha = ca->dctcp_alpha;
+			info->dctcp.dctcp_ab_ecn = tp->mss_cache *
+						   (tp->delivered_ce - ca->old_delivered_ce);
+			info->dctcp.dctcp_ab_tot = tp->mss_cache *
+						   (tp->delivered - ca->old_delivered);
+		}
+
+		*attr = INET_DIAG_DCTCPINFO;
+		return sizeof(info->dctcp);
+	}
+	return 0;
+}
+
+__bpf_kfunc static u32 dctcp_cwnd_undo(struct sock *sk)
+{
+	const struct dctcp *ca = inet_csk_ca(sk);
+	struct tcp_sock *tp = tcp_sk(sk);
+
+	return max(tcp_snd_cwnd(tp), ca->loss_cwnd);
+}
+
+static struct tcp_congestion_ops dctcp __read_mostly = {
+	.init		= dctcp_init,
+	.in_ack_event   = dctcp_update_alpha,
+	.cwnd_event	= dctcp_cwnd_event,
+	.cwnd_event_tx_start = dctcp_cwnd_event_tx_start,
+	.ssthresh	= dctcp_ssthresh,
+	.cong_avoid	= tcp_reno_cong_avoid,
+	.undo_cwnd	= dctcp_cwnd_undo,
+	.set_state	= dctcp_state,
+	.get_info	= dctcp_get_info,
+	.flags		= TCP_CONG_NEEDS_ECN,
+	.owner		= THIS_MODULE,
+	.name		= "dctcp",
+};
+
+static struct tcp_congestion_ops dctcp_reno __read_mostly = {
+	.ssthresh	= tcp_reno_ssthresh,
+	.cong_avoid	= tcp_reno_cong_avoid,
+	.undo_cwnd	= tcp_reno_undo_cwnd,
+	.get_info	= dctcp_get_info,
+	.owner		= THIS_MODULE,
+	.name		= "dctcp-reno",
+};
+
+BTF_KFUNCS_START(tcp_dctcp_check_kfunc_ids)
+BTF_ID_FLAGS(func, dctcp_init)
+BTF_ID_FLAGS(func, dctcp_update_alpha)
+BTF_ID_FLAGS(func, dctcp_cwnd_event)
+BTF_ID_FLAGS(func, dctcp_cwnd_event_tx_start)
+BTF_ID_FLAGS(func, dctcp_ssthresh)
+BTF_ID_FLAGS(func, dctcp_cwnd_undo)
+BTF_ID_FLAGS(func, dctcp_state)
+BTF_KFUNCS_END(tcp_dctcp_check_kfunc_ids)
+
+static const struct btf_kfunc_id_set tcp_dctcp_kfunc_set = {
+	.owner = THIS_MODULE,
+	.set   = &tcp_dctcp_check_kfunc_ids,
+};
+
+static int __init dctcp_register(void)
+{
+	int ret;
+
+	BUILD_BUG_ON(sizeof(struct dctcp) > ICSK_CA_PRIV_SIZE);
+
+	ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS, &tcp_dctcp_kfunc_set);
+	if (ret < 0)
+		return ret;
+	return tcp_register_congestion_control(&dctcp);
+}
+
+static void __exit dctcp_unregister(void)
+{
+	tcp_unregister_congestion_control(&dctcp);
+}
+
+module_init(dctcp_register);
+module_exit(dctcp_unregister);
+
+MODULE_AUTHOR("Daniel Borkmann <dborkman@redhat.com>");
+MODULE_AUTHOR("Florian Westphal <fw@strlen.de>");
+MODULE_AUTHOR("Glenn Judd <glenn.judd@morganstanley.com>");
+
+MODULE_LICENSE("GPL v2");
+MODULE_DESCRIPTION("DataCenter TCP (DCTCP)");