neigh_add() updates pneigh_entry() found or created by pneigh_create().

This update is serialised by RTNL, but we will remove it.

Let's move the update part to pneigh_create() and make it return errno
instead of a pointer of pneigh_entry.

Now, the pneigh code is RTNL free.

Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
---
 include/net/neighbour.h |  5 +++--
 net/core/neighbour.c    | 34 ++++++++++++++++------------------
 net/ipv4/arp.c          |  4 +---
 3 files changed, 20 insertions(+), 23 deletions(-)

diff --git a/include/net/neighbour.h b/include/net/neighbour.h
index f333f9ebc4259..4a30bd458c5a9 100644
--- a/include/net/neighbour.h
+++ b/include/net/neighbour.h
@@ -382,8 +382,9 @@ void pneigh_enqueue(struct neigh_table *tbl, struct neigh_parms *p,
 		    struct sk_buff *skb);
 struct pneigh_entry *pneigh_lookup(struct neigh_table *tbl, struct net *net,
 				   const void *key, struct net_device *dev);
-struct pneigh_entry *pneigh_create(struct neigh_table *tbl, struct net *net,
-				   const void *key, struct net_device *dev);
+int pneigh_create(struct neigh_table *tbl, struct net *net, const void *key,
+		  struct net_device *dev, u32 flags, u8 protocol,
+		  bool permanent);
 int pneigh_delete(struct neigh_table *tbl, struct net *net, const void *key,
 		  struct net_device *dev);
 
diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index 7e8a672dad6d1..7cd3cfe08b312 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -747,24 +747,27 @@ struct pneigh_entry *pneigh_lookup(struct neigh_table *tbl,
 }
 EXPORT_IPV6_MOD(pneigh_lookup);
 
-struct pneigh_entry *pneigh_create(struct neigh_table *tbl,
-				   struct net *net, const void *pkey,
-				   struct net_device *dev)
+int pneigh_create(struct neigh_table *tbl, struct net *net,
+		  const void *pkey, struct net_device *dev,
+		  u32 flags, u8 protocol, bool permanent)
 {
 	struct pneigh_entry *n;
 	unsigned int key_len;
 	u32 hash_val;
+	int err = 0;
 
 	mutex_lock(&tbl->phash_lock);
 
 	n = pneigh_lookup(tbl, net, pkey, dev);
 	if (n)
-		goto out;
+		goto update;
 
 	key_len = tbl->key_len;
 	n = kzalloc(sizeof(*n) + key_len, GFP_KERNEL);
-	if (!n)
+	if (!n) {
+		err = -ENOBUFS;
 		goto out;
+	}
 
 	write_pnet(&n->net, net);
 	memcpy(n->key, pkey, key_len);
@@ -774,16 +777,20 @@ struct pneigh_entry *pneigh_create(struct neigh_table *tbl,
 	if (tbl->pconstructor && tbl->pconstructor(n)) {
 		netdev_put(dev, &n->dev_tracker);
 		kfree(n);
-		n = NULL;
+		err = -ENOBUFS;
 		goto out;
 	}
 
 	hash_val = pneigh_hash(pkey, key_len);
 	n->next = tbl->phash_buckets[hash_val];
 	rcu_assign_pointer(tbl->phash_buckets[hash_val], n);
+update:
+	WRITE_ONCE(n->flags, flags);
+	n->permanent = permanent;
+	WRITE_ONCE(n->protocol, protocol);
 out:
 	mutex_unlock(&tbl->phash_lock);
-	return n;
+	return err;
 }
 
 static void pneigh_destroy(struct rcu_head *rcu)
@@ -2015,22 +2022,13 @@ static int neigh_add(struct sk_buff *skb, struct nlmsghdr *nlh,
 	if (tb[NDA_PROTOCOL])
 		protocol = nla_get_u8(tb[NDA_PROTOCOL]);
 	if (ndm_flags & NTF_PROXY) {
-		struct pneigh_entry *pn;
-
 		if (ndm_flags & (NTF_MANAGED | NTF_EXT_VALIDATED)) {
 			NL_SET_ERR_MSG(extack, "Invalid NTF_* flag combination");
 			goto out;
 		}
 
-		err = -ENOBUFS;
-		pn = pneigh_create(tbl, net, dst, dev);
-		if (pn) {
-			WRITE_ONCE(pn->flags, ndm_flags);
-			pn->permanent = !!(ndm->ndm_state & NUD_PERMANENT);
-			if (protocol)
-				WRITE_ONCE(pn->protocol, protocol);
-			err = 0;
-		}
+		err = pneigh_create(tbl, net, dst, dev, ndm_flags, protocol,
+				    !!(ndm->ndm_state & NUD_PERMANENT));
 		goto out;
 	}
 
diff --git a/net/ipv4/arp.c b/net/ipv4/arp.c
index d93b5735b0ba4..5cfc1c9396732 100644
--- a/net/ipv4/arp.c
+++ b/net/ipv4/arp.c
@@ -1089,9 +1089,7 @@ static int arp_req_set_public(struct net *net, struct arpreq *r,
 	if (mask) {
 		__be32 ip = ((struct sockaddr_in *)&r->arp_pa)->sin_addr.s_addr;
 
-		if (!pneigh_create(&arp_tbl, net, &ip, dev))
-			return -ENOBUFS;
-		return 0;
+		return pneigh_create(&arp_tbl, net, &ip, dev, 0, 0, false);
 	}
 
 	return arp_req_set_proxy(net, dev, 1);
-- 
2.50.0.727.gbf7dc18ff4-goog