net/mlx5e: Extend neigh hash entry with rcu

To remove dependency on rtnl lock and to allow unlocked iteration over list
of neigh hash entries, extend nhe with rcu. Change operations on neigh list
to their rcu counterparts and free neigh hash entry with rcu timeout.

Introduce mlx5e_get_next_nhe() helper that is used to iterate over rcu
neigh list with reference to nhe taken.
Signed-off-by: Vlad Buslov <vladbu@mellanox.com>
Reviewed-by: Jianbo Liu <jianbol@mellanox.com>
Reviewed-by: Roi Dayan <roid@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>

drivers/net/ethernet/mellanox/mlx5/core/en_rep.c

@@ -535,28 +535,56 @@ static void mlx5e_rep_neigh_entry_release(struct mlx5e_neigh_hash_entry *nhe)
 {
 	if (refcount_dec_and_test(&nhe->refcnt)) {
 		mlx5e_rep_neigh_entry_remove(nhe);
-		kfree(nhe);
+		kfree_rcu(nhe, rcu);
 	}
 }
 
+static struct mlx5e_neigh_hash_entry *
+mlx5e_get_next_nhe(struct mlx5e_rep_priv *rpriv,
+		   struct mlx5e_neigh_hash_entry *nhe)
+{
+	struct mlx5e_neigh_hash_entry *next = NULL;
+
+	rcu_read_lock();
+
+	for (next = nhe ?
+		     list_next_or_null_rcu(&rpriv->neigh_update.neigh_list,
+					   &nhe->neigh_list,
+					   struct mlx5e_neigh_hash_entry,
+					   neigh_list) :
+		     list_first_or_null_rcu(&rpriv->neigh_update.neigh_list,
+					    struct mlx5e_neigh_hash_entry,
+					    neigh_list);
+	     next;
+	     next = list_next_or_null_rcu(&rpriv->neigh_update.neigh_list,
+					  &next->neigh_list,
+					  struct mlx5e_neigh_hash_entry,
+					  neigh_list))
+		if (mlx5e_rep_neigh_entry_hold(next))
+			break;
+
+	rcu_read_unlock();
+
+	if (nhe)
+		mlx5e_rep_neigh_entry_release(nhe);
+
+	return next;
+}
+
 static void mlx5e_rep_neigh_stats_work(struct work_struct *work)
 {
 	struct mlx5e_rep_priv *rpriv = container_of(work, struct mlx5e_rep_priv,
 						    neigh_update.neigh_stats_work.work);
 	struct net_device *netdev = rpriv->netdev;
 	struct mlx5e_priv *priv = netdev_priv(netdev);
-	struct mlx5e_neigh_hash_entry *nhe;
+	struct mlx5e_neigh_hash_entry *nhe = NULL;
 
 	rtnl_lock();
 	if (!list_empty(&rpriv->neigh_update.neigh_list))
 		mlx5e_rep_queue_neigh_stats_work(priv);
 
-	list_for_each_entry(nhe, &rpriv->neigh_update.neigh_list, neigh_list) {
-		if (mlx5e_rep_neigh_entry_hold(nhe)) {
-			mlx5e_tc_update_neigh_used_value(nhe);
-			mlx5e_rep_neigh_entry_release(nhe);
-		}
-	}
+	while ((nhe = mlx5e_get_next_nhe(rpriv, nhe)) != NULL)
+		mlx5e_tc_update_neigh_used_value(nhe);
 
 	rtnl_unlock();
 }
@@ -883,13 +911,9 @@ static int mlx5e_rep_netevent_event(struct notifier_block *nb,
 		m_neigh.family = n->ops->family;
 		memcpy(&m_neigh.dst_ip, n->primary_key, n->tbl->key_len);
 
-		/* We are in atomic context and can't take RTNL mutex, so use
-		 * spin_lock_bh to lookup the neigh table. bh is used since
-		 * netevent can be called from a softirq context.
-		 */
-		spin_lock_bh(&neigh_update->encap_lock);
+		rcu_read_lock();
 		nhe = mlx5e_rep_neigh_entry_lookup(priv, &m_neigh);
-		spin_unlock_bh(&neigh_update->encap_lock);
+		rcu_read_unlock();
 		if (!nhe)
 			return NOTIFY_DONE;
 
@@ -910,19 +934,15 @@ static int mlx5e_rep_netevent_event(struct notifier_block *nb,
 #endif
 			return NOTIFY_DONE;
 
-		/* We are in atomic context and can't take RTNL mutex,
-		 * so use spin_lock_bh to walk the neigh list and look for
-		 * the relevant device. bh is used since netevent can be
-		 * called from a softirq context.
-		 */
-		spin_lock_bh(&neigh_update->encap_lock);
-		list_for_each_entry(nhe, &neigh_update->neigh_list, neigh_list) {
+		rcu_read_lock();
+		list_for_each_entry_rcu(nhe, &neigh_update->neigh_list,
+					neigh_list) {
 			if (p->dev == nhe->m_neigh.dev) {
 				found = true;
 				break;
 			}
 		}
-		spin_unlock_bh(&neigh_update->encap_lock);
+		rcu_read_unlock();
 		if (!found)
 			return NOTIFY_DONE;
 
@@ -995,7 +1015,7 @@ static int mlx5e_rep_neigh_entry_insert(struct mlx5e_priv *priv,
 	if (err)
 		return err;
 
-	list_add(&nhe->neigh_list, &rpriv->neigh_update.neigh_list);
+	list_add_rcu(&nhe->neigh_list, &rpriv->neigh_update.neigh_list);
 
 	return err;
 }
@@ -1006,7 +1026,7 @@ static void mlx5e_rep_neigh_entry_remove(struct mlx5e_neigh_hash_entry *nhe)
 
 	spin_lock_bh(&rpriv->neigh_update.encap_lock);
 
-	list_del(&nhe->neigh_list);
+	list_del_rcu(&nhe->neigh_list);
 
 	rhashtable_remove_fast(&rpriv->neigh_update.neigh_ht,
 			       &nhe->rhash_node,

drivers/net/ethernet/mellanox/mlx5/core/en_rep.h

@@ -138,6 +138,8 @@ struct mlx5e_neigh_hash_entry {
 	 * 'used' value and avoid neigh deleting by the kernel.
 	 */
 	unsigned long reported_lastuse;
+
+	struct rcu_head rcu;
 };
 
 enum {