Merge branch 'tcp-remove-net-core-request_sock-c-and-no-longer-inline-__reqsk_free'

Eric Dumazet says:

====================
tcp: remove net/core/request_sock.c and no longer inline __reqsk_free()

After DCCP removal, net/core/request_sock.c makes no more sense.

Move reqsk_queue_alloc() and reqsk_fastopen_remove() to TCP files.

Then put __reqsk_free() out of line to save ~2 Kbytes of text.
====================

Link: https://patch.msgid.link/20260204055147.1682705-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: kuba-moo

include/net/request_sock.h

@@ -123,14 +123,7 @@ static inline struct sock *skb_steal_sock(struct sk_buff *skb,
 	return sk;
 }
 
-static inline void __reqsk_free(struct request_sock *req)
-{
-	req->rsk_ops->destructor(req);
-	if (req->rsk_listener)
-		sock_put(req->rsk_listener);
-	kfree(req->saved_syn);
-	kmem_cache_free(req->rsk_ops->slab, req);
-}
+void __reqsk_free(struct request_sock *req);
 
 static inline void reqsk_free(struct request_sock *req)
 {
@@ -196,8 +189,6 @@ struct request_sock_queue {
 					     */
 };
 
-void reqsk_queue_alloc(struct request_sock_queue *queue);
-
 void reqsk_fastopen_remove(struct sock *sk, struct request_sock *req,
 			   bool reset);
 

net/core/Makefile

@@ -3,7 +3,7 @@
 # Makefile for the Linux networking core.
 #
 
-obj-y := sock.o request_sock.o skbuff.o datagram.o stream.o scm.o \
+obj-y := sock.o skbuff.o datagram.o stream.o scm.o \
 	 gen_stats.o gen_estimator.o net_namespace.o secure_seq.o \
 	 flow_dissector.o
 

net/core/request_sock.c

@@ -919,6 +919,16 @@ struct request_sock *inet_reqsk_alloc(const struct request_sock_ops *ops,
 }
 EXPORT_SYMBOL(inet_reqsk_alloc);
 
+void __reqsk_free(struct request_sock *req)
+{
+	req->rsk_ops->destructor(req);
+	if (req->rsk_listener)
+		sock_put(req->rsk_listener);
+	kfree(req->saved_syn);
+	kmem_cache_free(req->rsk_ops->slab, req);
+}
+EXPORT_SYMBOL_GPL(__reqsk_free);
+
 static struct request_sock *inet_reqsk_clone(struct request_sock *req,
 					     struct sock *sk)
 {
@@ -1314,6 +1324,15 @@ static int inet_ulp_can_listen(const struct sock *sk)
 	return 0;
 }
 
+static void reqsk_queue_alloc(struct request_sock_queue *queue)
+{
+	queue->fastopenq.rskq_rst_head = NULL;
+	queue->fastopenq.rskq_rst_tail = NULL;
+	queue->fastopenq.qlen = 0;
+
+	queue->rskq_accept_head = NULL;
+}
+
 int inet_csk_listen_start(struct sock *sk)
 {
 	struct inet_connection_sock *icsk = inet_csk(sk);

net/ipv4/inet_connection_sock.c

@@ -5,6 +5,92 @@
 #include <net/tcp.h>
 #include <net/busy_poll.h>
 
+/*
+ * This function is called to set a Fast Open socket's "fastopen_rsk" field
+ * to NULL when a TFO socket no longer needs to access the request_sock.
+ * This happens only after 3WHS has been either completed or aborted (e.g.,
+ * RST is received).
+ *
+ * Before TFO, a child socket is created only after 3WHS is completed,
+ * hence it never needs to access the request_sock. things get a lot more
+ * complex with TFO. A child socket, accepted or not, has to access its
+ * request_sock for 3WHS processing, e.g., to retransmit SYN-ACK pkts,
+ * until 3WHS is either completed or aborted. Afterwards the req will stay
+ * until either the child socket is accepted, or in the rare case when the
+ * listener is closed before the child is accepted.
+ *
+ * In short, a request socket is only freed after BOTH 3WHS has completed
+ * (or aborted) and the child socket has been accepted (or listener closed).
+ * When a child socket is accepted, its corresponding req->sk is set to
+ * NULL since it's no longer needed. More importantly, "req->sk == NULL"
+ * will be used by the code below to determine if a child socket has been
+ * accepted or not, and the check is protected by the fastopenq->lock
+ * described below.
+ *
+ * Note that fastopen_rsk is only accessed from the child socket's context
+ * with its socket lock held. But a request_sock (req) can be accessed by
+ * both its child socket through fastopen_rsk, and a listener socket through
+ * icsk_accept_queue.rskq_accept_head. To protect the access a simple spin
+ * lock per listener "icsk->icsk_accept_queue.fastopenq->lock" is created.
+ * only in the rare case when both the listener and the child locks are held,
+ * e.g., in inet_csk_listen_stop() do we not need to acquire the lock.
+ * The lock also protects other fields such as fastopenq->qlen, which is
+ * decremented by this function when fastopen_rsk is no longer needed.
+ *
+ * Note that another solution was to simply use the existing socket lock
+ * from the listener. But first socket lock is difficult to use. It is not
+ * a simple spin lock - one must consider sock_owned_by_user() and arrange
+ * to use sk_add_backlog() stuff. But what really makes it infeasible is the
+ * locking hierarchy violation. E.g., inet_csk_listen_stop() may try to
+ * acquire a child's lock while holding listener's socket lock.
+ *
+ * This function also sets "treq->tfo_listener" to false.
+ * treq->tfo_listener is used by the listener so it is protected by the
+ * fastopenq->lock in this function.
+ */
+void reqsk_fastopen_remove(struct sock *sk, struct request_sock *req,
+			   bool reset)
+{
+	struct sock *lsk = req->rsk_listener;
+	struct fastopen_queue *fastopenq;
+
+	fastopenq = &inet_csk(lsk)->icsk_accept_queue.fastopenq;
+
+	RCU_INIT_POINTER(tcp_sk(sk)->fastopen_rsk, NULL);
+	spin_lock_bh(&fastopenq->lock);
+	fastopenq->qlen--;
+	tcp_rsk(req)->tfo_listener = false;
+	if (req->sk)	/* the child socket hasn't been accepted yet */
+		goto out;
+
+	if (!reset || lsk->sk_state != TCP_LISTEN) {
+		/* If the listener has been closed don't bother with the
+		 * special RST handling below.
+		 */
+		spin_unlock_bh(&fastopenq->lock);
+		reqsk_put(req);
+		return;
+	}
+	/* Wait for 60secs before removing a req that has triggered RST.
+	 * This is a simple defense against TFO spoofing attack - by
+	 * counting the req against fastopen.max_qlen, and disabling
+	 * TFO when the qlen exceeds max_qlen.
+	 *
+	 * For more details see CoNext'11 "TCP Fast Open" paper.
+	 */
+	req->rsk_timer.expires = jiffies + 60*HZ;
+	if (fastopenq->rskq_rst_head == NULL)
+		fastopenq->rskq_rst_head = req;
+	else
+		fastopenq->rskq_rst_tail->dl_next = req;
+
+	req->dl_next = NULL;
+	fastopenq->rskq_rst_tail = req;
+	fastopenq->qlen++;
+out:
+	spin_unlock_bh(&fastopenq->lock);
+}
+
 void tcp_fastopen_init_key_once(struct net *net)
 {
 	u8 key[TCP_FASTOPEN_KEY_LENGTH];