net: use unrcu_pointer() helper

Toke mentioned unrcu_pointer() existence, allowing
to remove some of the ugly casts we have when using
xchg() for rcu protected pointers.

Also make inet_rcv_compat const.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Toke Høiland-Jørgensen <toke@redhat.com>
Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>
Link: https://lore.kernel.org/r/20240604111603.45871-1-edumazet@google.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

include/net/sock.h

@@ -2095,7 +2095,7 @@ sk_dst_set(struct sock *sk, struct dst_entry *dst)
 
 	sk_tx_queue_clear(sk);
 	WRITE_ONCE(sk->sk_dst_pending_confirm, 0);
-	old_dst = xchg((__force struct dst_entry **)&sk->sk_dst_cache, dst);
+	old_dst = unrcu_pointer(xchg(&sk->sk_dst_cache, RCU_INITIALIZER(dst)));
 	dst_release(old_dst);
 }
 

net/core/gen_estimator.c

@@ -206,7 +206,7 @@ void gen_kill_estimator(struct net_rate_estimator __rcu **rate_est)
 {
 	struct net_rate_estimator *est;
 
-	est = xchg((__force struct net_rate_estimator **)rate_est, NULL);
+	est = unrcu_pointer(xchg(rate_est, NULL));
 	if (est) {
 		timer_shutdown_sync(&est->timer);
 		kfree_rcu(est, rcu);

net/core/sock_diag.c

@@ -18,7 +18,7 @@
 
 static const struct sock_diag_handler __rcu *sock_diag_handlers[AF_MAX];
 
-static struct sock_diag_inet_compat __rcu *inet_rcv_compat;
+static const struct sock_diag_inet_compat __rcu *inet_rcv_compat;
 
 static struct workqueue_struct *broadcast_wq;
 
@@ -187,8 +187,7 @@ void sock_diag_broadcast_destroy(struct sock *sk)
 
 void sock_diag_register_inet_compat(const struct sock_diag_inet_compat *ptr)
 {
-	xchg((__force const struct sock_diag_inet_compat **)&inet_rcv_compat,
-	     ptr);
+	xchg(&inet_rcv_compat, RCU_INITIALIZER(ptr));
 }
 EXPORT_SYMBOL_GPL(sock_diag_register_inet_compat);
 
@@ -196,8 +195,7 @@ void sock_diag_unregister_inet_compat(const struct sock_diag_inet_compat *ptr)
 {
 	const struct sock_diag_inet_compat *old;
 
-	old = xchg((__force const struct sock_diag_inet_compat **)&inet_rcv_compat,
-		   NULL);
+	old = unrcu_pointer(xchg(&inet_rcv_compat, NULL));
 	WARN_ON_ONCE(old != ptr);
 }
 EXPORT_SYMBOL_GPL(sock_diag_unregister_inet_compat);

net/ipv4/cipso_ipv4.c

@@ -1953,7 +1953,7 @@ int cipso_v4_req_setattr(struct request_sock *req,
 	buf = NULL;
 
 	req_inet = inet_rsk(req);
-	opt = xchg((__force struct ip_options_rcu **)&req_inet->ireq_opt, opt);
+	opt = unrcu_pointer(xchg(&req_inet->ireq_opt, RCU_INITIALIZER(opt)));
 	if (opt)
 		kfree_rcu(opt, rcu);
 

net/ipv4/tcp.c

@@ -3081,7 +3081,7 @@ int tcp_disconnect(struct sock *sk, int flags)
 	icsk->icsk_ack.rcv_mss = TCP_MIN_MSS;
 	memset(&tp->rx_opt, 0, sizeof(tp->rx_opt));
 	__sk_dst_reset(sk);
-	dst_release(xchg((__force struct dst_entry **)&sk->sk_rx_dst, NULL));
+	dst_release(unrcu_pointer(xchg(&sk->sk_rx_dst, NULL)));
 	tcp_saved_syn_free(tp);
 	tp->compressed_ack = 0;
 	tp->segs_in = 0;

net/ipv4/tcp_fastopen.c

@@ -49,7 +49,7 @@ void tcp_fastopen_ctx_destroy(struct net *net)
 {
 	struct tcp_fastopen_context *ctxt;
 
-	ctxt = xchg((__force struct tcp_fastopen_context **)&net->ipv4.tcp_fastopen_ctx, NULL);
+	ctxt = unrcu_pointer(xchg(&net->ipv4.tcp_fastopen_ctx, NULL));
 
 	if (ctxt)
 		call_rcu(&ctxt->rcu, tcp_fastopen_ctx_free);
@@ -80,9 +80,10 @@ int tcp_fastopen_reset_cipher(struct net *net, struct sock *sk,
 
 	if (sk) {
 		q = &inet_csk(sk)->icsk_accept_queue.fastopenq;
-		octx = xchg((__force struct tcp_fastopen_context **)&q->ctx, ctx);
+		octx = unrcu_pointer(xchg(&q->ctx, RCU_INITIALIZER(ctx)));
 	} else {
-		octx = xchg((__force struct tcp_fastopen_context **)&net->ipv4.tcp_fastopen_ctx, ctx);
+		octx = unrcu_pointer(xchg(&net->ipv4.tcp_fastopen_ctx,
+					  RCU_INITIALIZER(ctx)));
 	}
 
 	if (octx)

net/ipv4/udp.c

@@ -2230,7 +2230,7 @@ bool udp_sk_rx_dst_set(struct sock *sk, struct dst_entry *dst)
 	struct dst_entry *old;
 
 	if (dst_hold_safe(dst)) {
-		old = xchg((__force struct dst_entry **)&sk->sk_rx_dst, dst);
+		old = unrcu_pointer(xchg(&sk->sk_rx_dst, RCU_INITIALIZER(dst)));
 		dst_release(old);
 		return old != dst;
 	}

net/ipv6/af_inet6.c

@@ -509,7 +509,7 @@ void inet6_cleanup_sock(struct sock *sk)
 
 	/* Free tx options */
 
-	opt = xchg((__force struct ipv6_txoptions **)&np->opt, NULL);
+	opt = unrcu_pointer(xchg(&np->opt, NULL));
 	if (opt) {
 		atomic_sub(opt->tot_len, &sk->sk_omem_alloc);
 		txopt_put(opt);

net/ipv6/ip6_fib.c

@@ -984,7 +984,7 @@ static void __fib6_drop_pcpu_from(struct fib6_nh *fib6_nh,
 		if (pcpu_rt && rcu_access_pointer(pcpu_rt->from) == match) {
 			struct fib6_info *from;
 
-			from = xchg((__force struct fib6_info **)&pcpu_rt->from, NULL);
+			from = unrcu_pointer(xchg(&pcpu_rt->from, NULL));
 			fib6_info_release(from);
 		}
 	}

net/ipv6/ipv6_sockglue.c

@@ -111,8 +111,7 @@ struct ipv6_txoptions *ipv6_update_options(struct sock *sk,
 			icsk->icsk_sync_mss(sk, icsk->icsk_pmtu_cookie);
 		}
 	}
-	opt = xchg((__force struct ipv6_txoptions **)&inet6_sk(sk)->opt,
-		   opt);
+	opt = unrcu_pointer(xchg(&inet6_sk(sk)->opt, RCU_INITIALIZER(opt)));
 	sk_dst_reset(sk);
 
 	return opt;

net/ipv6/route.c

@@ -368,7 +368,7 @@ static void ip6_dst_destroy(struct dst_entry *dst)
 		in6_dev_put(idev);
 	}
 
-	from = xchg((__force struct fib6_info **)&rt->from, NULL);
+	from = unrcu_pointer(xchg(&rt->from, NULL));
 	fib6_info_release(from);
 }
 
@@ -1437,7 +1437,7 @@ static struct rt6_info *rt6_make_pcpu_route(struct net *net,
 	if (res->f6i->fib6_destroying) {
 		struct fib6_info *from;
 
-		from = xchg((__force struct fib6_info **)&pcpu_rt->from, NULL);
+		from = unrcu_pointer(xchg(&pcpu_rt->from, NULL));
 		fib6_info_release(from);
 	}
 
@@ -1466,7 +1466,7 @@ static void rt6_remove_exception(struct rt6_exception_bucket *bucket,
 	/* purge completely the exception to allow releasing the held resources:
 	 * some [sk] cache may keep the dst around for unlimited time
 	 */
-	from = xchg((__force struct fib6_info **)&rt6_ex->rt6i->from, NULL);
+	from = unrcu_pointer(xchg(&rt6_ex->rt6i->from, NULL));
 	fib6_info_release(from);
 	dst_dev_put(&rt6_ex->rt6i->dst);
 

net/sched/act_api.c

@@ -62,7 +62,7 @@ static void tcf_set_action_cookie(struct tc_cookie __rcu **old_cookie,
 {
 	struct tc_cookie *old;
 
-	old = xchg((__force struct tc_cookie **)old_cookie, new_cookie);
+	old = unrcu_pointer(xchg(old_cookie, RCU_INITIALIZER(new_cookie)));
 	if (old)
 		call_rcu(&old->rcu, tcf_free_cookie_rcu);
 }