net: add {READ|WRITE}_ONCE() annotations on ->rskq_accept_head

reqsk_queue_empty() is called from inet_csk_listen_poll() while
other cpus might write ->rskq_accept_head value.

Use {READ|WRITE}_ONCE() to avoid compiler tricks
and potential KCSAN splats.

Fixes: fff1f300 ("tcp: add a spinlock to protect struct request_sock_queue")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>

drivers/xen/pvcalls-back.c

@@ -775,7 +775,7 @@ static int pvcalls_back_poll(struct xenbus_device *dev,
 	mappass->reqcopy = *req;
 	icsk = inet_csk(mappass->sock->sk);
 	queue = &icsk->icsk_accept_queue;
-	data = queue->rskq_accept_head != NULL;
+	data = READ_ONCE(queue->rskq_accept_head) != NULL;
 	if (data) {
 		mappass->reqcopy.cmd = 0;
 		ret = 0;

include/net/request_sock.h

@@ -185,7 +185,7 @@ void reqsk_fastopen_remove(struct sock *sk, struct request_sock *req,
 
 static inline bool reqsk_queue_empty(const struct request_sock_queue *queue)
 {
-	return queue->rskq_accept_head == NULL;
+	return READ_ONCE(queue->rskq_accept_head) == NULL;
 }
 
 static inline struct request_sock *reqsk_queue_remove(struct request_sock_queue *queue,
@@ -197,7 +197,7 @@ static inline struct request_sock *reqsk_queue_remove(struct request_sock_queue
 	req = queue->rskq_accept_head;
 	if (req) {
 		sk_acceptq_removed(parent);
-		queue->rskq_accept_head = req->dl_next;
+		WRITE_ONCE(queue->rskq_accept_head, req->dl_next);
 		if (queue->rskq_accept_head == NULL)
 			queue->rskq_accept_tail = NULL;
 	}

net/ipv4/inet_connection_sock.c

@@ -934,7 +934,7 @@ struct sock *inet_csk_reqsk_queue_add(struct sock *sk,
 		req->sk = child;
 		req->dl_next = NULL;
 		if (queue->rskq_accept_head == NULL)
-			queue->rskq_accept_head = req;
+			WRITE_ONCE(queue->rskq_accept_head, req);
 		else
 			queue->rskq_accept_tail->dl_next = req;
 		queue->rskq_accept_tail = req;