neighbour: Remove __pneigh_lookup().

__pneigh_lookup() is the lockless version of pneigh_lookup(),
but its only caller pndisc_is_router() holds the table lock and
reads pneigh_netry.flags.

This is because accessing pneigh_entry after pneigh_lookup() was
illegal unless the caller holds RTNL or the table lock.

Now, pneigh_entry is guaranteed to be alive during the RCU critical
section.

Let's call pneigh_lookup() and use READ_ONCE() for n->flags in
pndisc_is_router() and remove __pneigh_lookup().

Signed-off-by: Kuniyuki Iwashima <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: q2ven

include/net/neighbour.h

@@ -381,8 +381,6 @@ 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_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_delete(struct neigh_table *tbl, struct net *net, const void *key,

net/core/neighbour.c

@@ -737,17 +737,6 @@ static struct pneigh_entry *__pneigh_lookup_1(struct pneigh_entry *n,
 	return NULL;
 }
 
-struct pneigh_entry *__pneigh_lookup(struct neigh_table *tbl,
-		struct net *net, const void *pkey, struct net_device *dev)
-{
-	unsigned int key_len = tbl->key_len;
-	u32 hash_val = pneigh_hash(pkey, key_len);
-
-	return __pneigh_lookup_1(rcu_dereference_protected(tbl->phash_buckets[hash_val], 1),
-				 net, pkey, key_len, dev);
-}
-EXPORT_SYMBOL_GPL(__pneigh_lookup);
-
 struct pneigh_entry *pneigh_lookup(struct neigh_table *tbl,
 				   struct net *net, const void *pkey,
 				   struct net_device *dev)

net/ipv6/ndisc.c

@@ -768,11 +768,9 @@ static int pndisc_is_router(const void *pkey,
 	struct pneigh_entry *n;
 	int ret = -1;
 
-	read_lock_bh(&nd_tbl.lock);
-	n = __pneigh_lookup(&nd_tbl, dev_net(dev), pkey, dev);
+	n = pneigh_lookup(&nd_tbl, dev_net(dev), pkey, dev);
 	if (n)
-		ret = !!(n->flags & NTF_ROUTER);
-	read_unlock_bh(&nd_tbl.lock);
+		ret = !!(READ_ONCE(n->flags) & NTF_ROUTER);
 
 	return ret;
 }