hsr: Use a single struct for self_node.

self_node_db is a list_head with one entry of struct hsr_node. The
purpose is to hold the two MAC addresses of the node itself.
It is convenient to recycle the structure. However having a list_head
and fetching always the first entry is not really optimal.

Created a new data strucure contaning the two MAC addresses named
hsr_self_node. Access that structure like an RCU protected pointer so
it can be replaced on the fly without blocking the reader.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Kurt Kanzenbach <kurt@linutronix.de>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/hsr/hsr_device.c

@@ -490,7 +490,6 @@ int hsr_dev_finalize(struct net_device *hsr_dev, struct net_device *slave[2],
 	hsr = netdev_priv(hsr_dev);
 	INIT_LIST_HEAD(&hsr->ports);
 	INIT_LIST_HEAD(&hsr->node_db);
-	INIT_LIST_HEAD(&hsr->self_node_db);
 	spin_lock_init(&hsr->list_lock);
 
 	eth_hw_addr_set(hsr_dev, slave[0]->dev_addr);

net/hsr/hsr_framereg.c

@@ -38,21 +38,22 @@ static bool seq_nr_after(u16 a, u16 b)
 
 bool hsr_addr_is_self(struct hsr_priv *hsr, unsigned char *addr)
 {
-	struct hsr_node *node;
+	struct hsr_self_node *sn;
+	bool ret = false;
 
-	node = list_first_or_null_rcu(&hsr->self_node_db, struct hsr_node,
-				      mac_list);
-	if (!node) {
+	rcu_read_lock();
+	sn = rcu_dereference(hsr->self_node);
+	if (!sn) {
 		WARN_ONCE(1, "HSR: No self node\n");
-		return false;
+		goto out;
 	}
 
-	if (ether_addr_equal(addr, node->macaddress_A))
-		return true;
-	if (ether_addr_equal(addr, node->macaddress_B))
-		return true;
-
-	return false;
+	if (ether_addr_equal(addr, sn->macaddress_A) ||
+	    ether_addr_equal(addr, sn->macaddress_B))
+		ret = true;
+out:
+	rcu_read_unlock();
+	return ret;
 }
 
 /* Search for mac entry. Caller must hold rcu read lock.
@@ -70,50 +71,42 @@ static struct hsr_node *find_node_by_addr_A(struct list_head *node_db,
 	return NULL;
 }
 
-/* Helper for device init; the self_node_db is used in hsr_rcv() to recognize
+/* Helper for device init; the self_node is used in hsr_rcv() to recognize
  * frames from self that's been looped over the HSR ring.
  */
 int hsr_create_self_node(struct hsr_priv *hsr,
 			 const unsigned char addr_a[ETH_ALEN],
 			 const unsigned char addr_b[ETH_ALEN])
 {
-	struct list_head *self_node_db = &hsr->self_node_db;
-	struct hsr_node *node, *oldnode;
+	struct hsr_self_node *sn, *old;
 
-	node = kmalloc(sizeof(*node), GFP_KERNEL);
-	if (!node)
+	sn = kmalloc(sizeof(*sn), GFP_KERNEL);
+	if (!sn)
 		return -ENOMEM;
 
-	ether_addr_copy(node->macaddress_A, addr_a);
-	ether_addr_copy(node->macaddress_B, addr_b);
+	ether_addr_copy(sn->macaddress_A, addr_a);
+	ether_addr_copy(sn->macaddress_B, addr_b);
 
 	spin_lock_bh(&hsr->list_lock);
-	oldnode = list_first_or_null_rcu(self_node_db,
-					 struct hsr_node, mac_list);
-	if (oldnode) {
-		list_replace_rcu(&oldnode->mac_list, &node->mac_list);
-		spin_unlock_bh(&hsr->list_lock);
-		kfree_rcu(oldnode, rcu_head);
-	} else {
-		list_add_tail_rcu(&node->mac_list, self_node_db);
-		spin_unlock_bh(&hsr->list_lock);
-	}
+	old = rcu_replace_pointer(hsr->self_node, sn,
+				  lockdep_is_held(&hsr->list_lock));
+	spin_unlock_bh(&hsr->list_lock);
 
+	if (old)
+		kfree_rcu(old, rcu_head);
 	return 0;
 }
 
 void hsr_del_self_node(struct hsr_priv *hsr)
 {
-	struct list_head *self_node_db = &hsr->self_node_db;
-	struct hsr_node *node;
+	struct hsr_self_node *old;
 
 	spin_lock_bh(&hsr->list_lock);
-	node = list_first_or_null_rcu(self_node_db, struct hsr_node, mac_list);
-	if (node) {
-		list_del_rcu(&node->mac_list);
-		kfree_rcu(node, rcu_head);
-	}
+	old = rcu_replace_pointer(hsr->self_node, NULL,
+				  lockdep_is_held(&hsr->list_lock));
 	spin_unlock_bh(&hsr->list_lock);
+	if (old)
+		kfree_rcu(old, rcu_head);
 }
 
 void hsr_del_nodes(struct list_head *node_db)

net/hsr/hsr_main.h

@@ -182,11 +182,17 @@ struct hsr_proto_ops {
 	void (*update_san_info)(struct hsr_node *node, bool is_sup);
 };
 
+struct hsr_self_node {
+	unsigned char	macaddress_A[ETH_ALEN];
+	unsigned char	macaddress_B[ETH_ALEN];
+	struct rcu_head	rcu_head;
+};
+
 struct hsr_priv {
 	struct rcu_head		rcu_head;
 	struct list_head	ports;
 	struct list_head	node_db;	/* Known HSR nodes */
-	struct list_head	self_node_db;	/* MACs of slaves */
+	struct hsr_self_node	__rcu *self_node;	/* MACs of slaves */
 	struct timer_list	announce_timer;	/* Supervision frame dispatch */
 	struct timer_list	prune_timer;
 	int announce_count;