Merge branch 'tcp-clean-up-syn-ack-rto-code-and-apply-max-rto'

Kuniyuki Iwashima says:

====================
tcp: Clean up SYN+ACK RTO code and apply max RTO.

Patch 1 - 4 are misc cleanup.

Patch 5 applies max RTO to non-TFO SYN+ACK.

Patch 6 adds a test for max RTO of SYN+ACK.
====================

Link: https://patch.msgid.link/20251106003357.273403-1-kuniyu@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

include/net/inet_connection_sock.h

@@ -267,8 +267,7 @@ struct dst_entry *inet_csk_route_child_sock(const struct sock *sk,
 struct sock *inet_csk_reqsk_queue_add(struct sock *sk,
 				      struct request_sock *req,
 				      struct sock *child);
-bool inet_csk_reqsk_queue_hash_add(struct sock *sk, struct request_sock *req,
-				   unsigned long timeout);
+bool inet_csk_reqsk_queue_hash_add(struct sock *sk, struct request_sock *req);
 struct sock *inet_csk_complete_hashdance(struct sock *sk, struct sock *child,
 					 struct request_sock *req,
 					 bool own_req);
@@ -291,14 +290,6 @@ static inline int inet_csk_reqsk_queue_is_full(const struct sock *sk)
 bool inet_csk_reqsk_queue_drop(struct sock *sk, struct request_sock *req);
 void inet_csk_reqsk_queue_drop_and_put(struct sock *sk, struct request_sock *req);
 
-static inline unsigned long
-reqsk_timeout(struct request_sock *req, unsigned long max_timeout)
-{
-	u64 timeout = (u64)req->timeout << req->num_timeout;
-
-	return (unsigned long)min_t(u64, timeout, max_timeout);
-}
-
 void inet_csk_destroy_sock(struct sock *sk);
 void inet_csk_prepare_for_destroy_sock(struct sock *sk);
 void inet_csk_prepare_forced_close(struct sock *sk);

include/net/request_sock.h

@@ -36,7 +36,6 @@ struct request_sock_ops {
 				      struct sk_buff *skb,
 				      enum sk_rst_reason reason);
 	void		(*destructor)(struct request_sock *req);
-	void		(*syn_ack_timeout)(const struct request_sock *req);
 };
 
 struct saved_syn {

include/net/tcp.h

@@ -841,6 +841,14 @@ static inline u32 __tcp_set_rto(const struct tcp_sock *tp)
 	return usecs_to_jiffies((tp->srtt_us >> 3) + tp->rttvar_us);
 }
 
+static inline unsigned long tcp_reqsk_timeout(struct request_sock *req)
+{
+	u64 timeout = (u64)req->timeout << req->num_timeout;
+
+	return (unsigned long)min_t(u64, timeout,
+				    tcp_rto_max(req->rsk_listener));
+}
+
 u32 tcp_delack_max(const struct sock *sk);
 
 /* Compute the actual rto_min value */

net/ipv4/inet_connection_sock.c

@@ -885,7 +885,6 @@ reqsk_alloc_noprof(const struct request_sock_ops *ops, struct sock *sk_listener,
 	sk_tx_queue_clear(req_to_sk(req));
 	req->saved_syn = NULL;
 	req->syncookie = 0;
-	req->timeout = 0;
 	req->num_timeout = 0;
 	req->num_retrans = 0;
 	req->sk = NULL;
@@ -913,7 +912,6 @@ struct request_sock *inet_reqsk_alloc(const struct request_sock_ops *ops,
 		ireq->ireq_state = TCP_NEW_SYN_RECV;
 		write_pnet(&ireq->ireq_net, sock_net(sk_listener));
 		ireq->ireq_family = sk_listener->sk_family;
-		req->timeout = TCP_TIMEOUT_INIT;
 	}
 
 	return req;
@@ -1096,16 +1094,18 @@ static void reqsk_timer_handler(struct timer_list *t)
 			young <<= 1;
 		}
 	}
+
 	syn_ack_recalc(req, max_syn_ack_retries, READ_ONCE(queue->rskq_defer_accept),
 		       &expire, &resend);
-	req->rsk_ops->syn_ack_timeout(req);
+	tcp_syn_ack_timeout(req);
+
 	if (!expire &&
 	    (!resend ||
 	     !tcp_rtx_synack(sk_listener, req) ||
 	     inet_rsk(req)->acked)) {
 		if (req->num_timeout++ == 0)
 			atomic_dec(&queue->young);
-		mod_timer(&req->rsk_timer, jiffies + reqsk_timeout(req, TCP_RTO_MAX));
+		mod_timer(&req->rsk_timer, jiffies + tcp_reqsk_timeout(req));
 
 		if (!nreq)
 			return;
@@ -1142,8 +1142,7 @@ drop:
 	reqsk_put(oreq);
 }
 
-static bool reqsk_queue_hash_req(struct request_sock *req,
-				 unsigned long timeout)
+static bool reqsk_queue_hash_req(struct request_sock *req)
 {
 	bool found_dup_sk = false;
 
@@ -1151,8 +1150,9 @@ static bool reqsk_queue_hash_req(struct request_sock *req,
 		return false;
 
 	/* The timer needs to be setup after a successful insertion. */
+	req->timeout = tcp_timeout_init((struct sock *)req);
 	timer_setup(&req->rsk_timer, reqsk_timer_handler, TIMER_PINNED);
-	mod_timer(&req->rsk_timer, jiffies + timeout);
+	mod_timer(&req->rsk_timer, jiffies + req->timeout);
 
 	/* before letting lookups find us, make sure all req fields
 	 * are committed to memory and refcnt initialized.
@@ -1162,10 +1162,9 @@ static bool reqsk_queue_hash_req(struct request_sock *req,
 	return true;
 }
 
-bool inet_csk_reqsk_queue_hash_add(struct sock *sk, struct request_sock *req,
-				   unsigned long timeout)
+bool inet_csk_reqsk_queue_hash_add(struct sock *sk, struct request_sock *req)
 {
-	if (!reqsk_queue_hash_req(req, timeout))
+	if (!reqsk_queue_hash_req(req))
 		return false;
 
 	inet_csk_reqsk_queue_added(sk);

net/ipv4/tcp_input.c

@@ -7531,15 +7531,11 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
 		sock_put(fastopen_sk);
 	} else {
 		tcp_rsk(req)->tfo_listener = false;
-		if (!want_cookie) {
-			req->timeout = tcp_timeout_init((struct sock *)req);
-			if (unlikely(!inet_csk_reqsk_queue_hash_add(sk, req,
-								    req->timeout))) {
-				reqsk_free(req);
-				dst_release(dst);
-				return 0;
-			}
-
+		if (!want_cookie &&
+		    unlikely(!inet_csk_reqsk_queue_hash_add(sk, req))) {
+			reqsk_free(req);
+			dst_release(dst);
+			return 0;
 		}
 		af_ops->send_synack(sk, dst, &fl, req, &foc,
 				    !want_cookie ? TCP_SYNACK_NORMAL :

net/ipv4/tcp_ipv4.c

@@ -1660,7 +1660,6 @@ struct request_sock_ops tcp_request_sock_ops __read_mostly = {
 	.send_ack	=	tcp_v4_reqsk_send_ack,
 	.destructor	=	tcp_v4_reqsk_destructor,
 	.send_reset	=	tcp_v4_send_reset,
-	.syn_ack_timeout =	tcp_syn_ack_timeout,
 };
 
 const struct tcp_request_sock_ops tcp_request_sock_ipv4_ops = {

net/ipv4/tcp_minisocks.c

@@ -714,7 +714,8 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
 			 * it can be estimated (approximately)
 			 * from another data.
 			 */
-			tmp_opt.ts_recent_stamp = ktime_get_seconds() - reqsk_timeout(req, TCP_RTO_MAX) / HZ;
+			tmp_opt.ts_recent_stamp = ktime_get_seconds() -
+				tcp_reqsk_timeout(req) / HZ;
 			paws_reject = tcp_paws_reject(&tmp_opt, th->rst);
 		}
 	}
@@ -753,7 +754,7 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
 		    !tcp_rtx_synack(sk, req)) {
 			unsigned long expires = jiffies;
 
-			expires += reqsk_timeout(req, TCP_RTO_MAX);
+			expires += tcp_reqsk_timeout(req);
 			if (!fastopen)
 				mod_timer_pending(&req->rsk_timer, expires);
 			else

net/ipv4/tcp_timer.c

@@ -458,7 +458,7 @@ static void tcp_fastopen_synack_timer(struct sock *sk, struct request_sock *req)
 	struct tcp_sock *tp = tcp_sk(sk);
 	int max_retries;
 
-	req->rsk_ops->syn_ack_timeout(req);
+	tcp_syn_ack_timeout(req);
 
 	/* Add one more retry for fastopen.
 	 * Paired with WRITE_ONCE() in tcp_sock_set_syncnt()
@@ -752,7 +752,6 @@ void tcp_syn_ack_timeout(const struct request_sock *req)
 
 	__NET_INC_STATS(net, LINUX_MIB_TCPTIMEOUTS);
 }
-EXPORT_IPV6_MOD(tcp_syn_ack_timeout);
 
 void tcp_reset_keepalive_timer(struct sock *sk, unsigned long len)
 {

net/ipv6/tcp_ipv6.c

@@ -796,7 +796,6 @@ struct request_sock_ops tcp6_request_sock_ops __read_mostly = {
 	.send_ack	=	tcp_v6_reqsk_send_ack,
 	.destructor	=	tcp_v6_reqsk_destructor,
 	.send_reset	=	tcp_v6_send_reset,
-	.syn_ack_timeout =	tcp_syn_ack_timeout,
 };
 
 const struct tcp_request_sock_ops tcp_request_sock_ipv6_ops = {

tools/testing/selftests/net/packetdrill/tcp_rto_synack_rto_max.pkt

@@ -0,0 +1,54 @@
+// SPDX-License-Identifier: GPL-2.0
+//
+// Test SYN+ACK RTX with 1s RTO.
+//
+`./defaults.sh
+ ./set_sysctls.py /proc/sys/net/ipv4/tcp_rto_max_ms=1000`
+
+//
+// Test 1: TFO SYN+ACK
+//
+    0 socket(..., SOCK_STREAM|SOCK_NONBLOCK, IPPROTO_TCP) = 3
+   +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
+   +0 bind(3, ..., ...) = 0
+   +0 listen(3, 1) = 0
+   +0 setsockopt(3, SOL_TCP, TCP_FASTOPEN, [1], 4) = 0
+
+   +0 < S 0:10(10) win 1000 <mss 1460,sackOK,nop,nop,FO TFO_COOKIE,nop,nop>
+   +0 > S. 0:0(0) ack 11 <mss 1460,nop,nop,sackOK>
+
+// RTO must be capped to 1s
+   +1 > S. 0:0(0) ack 11 <mss 1460,nop,nop,sackOK>
+   +1 > S. 0:0(0) ack 11 <mss 1460,nop,nop,sackOK>
+   +1 > S. 0:0(0) ack 11 <mss 1460,nop,nop,sackOK>
+
+   +0 < . 11:11(0) ack 1 win 1000 <mss 1460,nop,nop,sackOK>
+   +0 accept(3, ..., ...) = 4
+   +0 %{ assert (tcpi_options & TCPI_OPT_SYN_DATA) != 0, tcpi_options }%
+
+   +0 close(4) = 0
+   +0 close(3) = 0
+
+
+//
+// Test 2: non-TFO SYN+ACK
+//
+   +0 socket(..., SOCK_STREAM|SOCK_NONBLOCK, IPPROTO_TCP) = 3
+   +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
+   +0 bind(3, ..., ...) = 0
+   +0 listen(3, 1) = 0
+
+   +0 < S 0:0(0) win 1000 <mss 1460,sackOK,nop,nop>
+   +0 > S. 0:0(0) ack 1 <mss 1460,nop,nop,sackOK>
+
+// RTO must be capped to 1s
+   +1 > S. 0:0(0) ack 1 <mss 1460,nop,nop,sackOK>
+   +1 > S. 0:0(0) ack 1 <mss 1460,nop,nop,sackOK>
+   +1 > S. 0:0(0) ack 1 <mss 1460,nop,nop,sackOK>
+
+   +0 < . 1:1(0) ack 1 win 1000 <mss 1460,nop,nop,sackOK>
+   +0 accept(3, ..., ...) = 4
+   +0 %{ assert (tcpi_options & TCPI_OPT_SYN_DATA) == 0, tcpi_options }%
+
+   +0 close(4) = 0
+   +0 close(3) = 0