rxrpc: Allow list of in-use local UDP endpoints to be viewed in /proc

Allow the list of in-use local UDP endpoints in the current network
namespace to be viewed in /proc.

To aid with this, the endpoint list is converted to an hlist and RCU-safe
manipulation is used so that the list can be read with only the RCU
read lock held.

Signed-off-by: David Howells <[e-mail]>
cc: Marc Dionne <[e-mail]>
cc: [e-mail]
Signed-off-by: David S. Miller <[e-mail]>

net/rxrpc/ar-internal.h

···
 	struct work_struct	client_conn_reaper;
 	struct timer_list	client_conn_reap_timer;
 
-	struct list_head	local_endpoints;
+	struct hlist_head	local_endpoints;
 	struct mutex		local_mutex;	/* Lock for ->local_endpoints */
 
 	DECLARE_HASHTABLE	(peer_hash, 10);
···
 	atomic_t		active_users;	/* Number of users of the local endpoint */
 	atomic_t		usage;		/* Number of references to the structure */
 	struct rxrpc_net	*rxnet;		/* The network ns in which this resides */
-	struct list_head	link;
+	struct hlist_node	link;
 	struct socket		*socket;	/* my UDP socket */
 	struct work_struct	processor;
 	struct rxrpc_sock __rcu	*service;	/* Service(s) listening on this endpoint */
···
 extern const struct seq_operations rxrpc_call_seq_ops;
 extern const struct seq_operations rxrpc_connection_seq_ops;
 extern const struct seq_operations rxrpc_peer_seq_ops;
+extern const struct seq_operations rxrpc_local_seq_ops;
 
 /*
  * recvmsg.c

net/rxrpc/local_object.c

···
 		atomic_set(&local->usage, 1);
 		atomic_set(&local->active_users, 1);
 		local->rxnet = rxnet;
-		INIT_LIST_HEAD(&local->link);
+		INIT_HLIST_NODE(&local->link);
 		INIT_WORK(&local->processor, rxrpc_local_processor);
 		init_rwsem(&local->defrag_sem);
 		skb_queue_head_init(&local->reject_queue);
···
 {
 	struct rxrpc_local *local;
 	struct rxrpc_net *rxnet = rxrpc_net(net);
-	struct list_head *cursor;
+	struct hlist_node *cursor;
 	const char *age;
 	long diff;
 	int ret;
···
 
 	mutex_lock(&rxnet->local_mutex);
 
-	for (cursor = rxnet->local_endpoints.next;
-	     cursor != &rxnet->local_endpoints;
-	     cursor = cursor->next) {
-		local = list_entry(cursor, struct rxrpc_local, link);
+	hlist_for_each(cursor, &rxnet->local_endpoints) {
+		local = hlist_entry(cursor, struct rxrpc_local, link);
 
 		diff = rxrpc_local_cmp_key(local, srx);
-		if (diff < 0)
+		if (diff != 0)
 			continue;
-		if (diff > 0)
-			break;
 
 		/* Services aren't allowed to share transport sockets, so
 		 * reject that here.  It is possible that the object is dying -
···
 			goto addr_in_use;
 		}
 
-		/* Found a match.  We replace a dying object.  Attempting to
-		 * bind the transport socket may still fail if we're attempting
-		 * to use a local address that the dying object is still using.
+		/* Found a match.  We want to replace a dying object.
+		 * Attempting to bind the transport socket may still fail if
+		 * we're attempting to use a local address that the dying
+		 * object is still using.
 		 */
 		if (!rxrpc_use_local(local))
 			break;
···
 	if (ret < 0)
 		goto sock_error;
 
-	if (cursor != &rxnet->local_endpoints)
-		list_replace_init(cursor, &local->link);
-	else
-		list_add_tail(&local->link, cursor);
+	if (cursor) {
+		hlist_replace_rcu(cursor, &local->link);
+		cursor->pprev = NULL;
+	} else {
+		hlist_add_head_rcu(&local->link, &rxnet->local_endpoints);
+	}
 	age = "new";
 
 found:
···
 	local->dead = true;
 
 	mutex_lock(&rxnet->local_mutex);
-	list_del_init(&local->link);
+	hlist_del_init_rcu(&local->link);
 	mutex_unlock(&rxnet->local_mutex);
 
 	rxrpc_clean_up_local_conns(local);
···
 
 	flush_workqueue(rxrpc_workqueue);
 
-	if (!list_empty(&rxnet->local_endpoints)) {
+	if (!hlist_empty(&rxnet->local_endpoints)) {
 		mutex_lock(&rxnet->local_mutex);
-		list_for_each_entry(local, &rxnet->local_endpoints, link) {
+		hlist_for_each_entry(local, &rxnet->local_endpoints, link) {
 			pr_err("AF_RXRPC: Leaked local %p {%d}\n",
 			       local, atomic_read(&local->usage));
 		}

net/rxrpc/net_ns.c

···
 	timer_setup(&rxnet->client_conn_reap_timer,
 		    rxrpc_client_conn_reap_timeout, 0);
 
-	INIT_LIST_HEAD(&rxnet->local_endpoints);
+	INIT_HLIST_HEAD(&rxnet->local_endpoints);
 	mutex_init(&rxnet->local_mutex);
 
 	hash_init(rxnet->peer_hash);
···
 			sizeof(struct seq_net_private));
 	proc_create_net("peers", 0444, rxnet->proc_net,
 			&rxrpc_peer_seq_ops,
+			sizeof(struct seq_net_private));
+	proc_create_net("locals", 0444, rxnet->proc_net,
+			&rxrpc_local_seq_ops,
 			sizeof(struct seq_net_private));
 	return 0;
 

net/rxrpc/proc.c

···
 	.stop   = rxrpc_peer_seq_stop,
 	.show   = rxrpc_peer_seq_show,
 };
+
+/*
+ * Generate a list of extant virtual local endpoints in /proc/net/rxrpc/locals
+ */
+static int rxrpc_local_seq_show(struct seq_file *seq, void *v)
+{
+	struct rxrpc_local *local;
+	char lbuff[50];
+
+	if (v == SEQ_START_TOKEN) {
+		seq_puts(seq,
+			 "Proto Local                                          "
+			 " Use Act\n");
+		return 0;
+	}
+
+	local = hlist_entry(v, struct rxrpc_local, link);
+
+	sprintf(lbuff, "%pISpc", &local->srx.transport);
+
+	seq_printf(seq,
+		   "UDP   %-47.47s %3u %3u\n",
+		   lbuff,
+		   atomic_read(&local->usage),
+		   atomic_read(&local->active_users));
+
+	return 0;
+}
+
+static void *rxrpc_local_seq_start(struct seq_file *seq, loff_t *_pos)
+	__acquires(rcu)
+{
+	struct rxrpc_net *rxnet = rxrpc_net(seq_file_net(seq));
+	unsigned int n;
+
+	rcu_read_lock();
+
+	if (*_pos >= UINT_MAX)
+		return NULL;
+
+	n = *_pos;
+	if (n == 0)
+		return SEQ_START_TOKEN;
+
+	return seq_hlist_start_rcu(&rxnet->local_endpoints, n - 1);
+}
+
+static void *rxrpc_local_seq_next(struct seq_file *seq, void *v, loff_t *_pos)
+{
+	struct rxrpc_net *rxnet = rxrpc_net(seq_file_net(seq));
+
+	if (*_pos >= UINT_MAX)
+		return NULL;
+
+	return seq_hlist_next_rcu(v, &rxnet->local_endpoints, _pos);
+}
+
+static void rxrpc_local_seq_stop(struct seq_file *seq, void *v)
+	__releases(rcu)
+{
+	rcu_read_unlock();
+}
+
+const struct seq_operations rxrpc_local_seq_ops = {
+	.start  = rxrpc_local_seq_start,
+	.next   = rxrpc_local_seq_next,
+	.stop   = rxrpc_local_seq_stop,
+	.show   = rxrpc_local_seq_show,
+};