netfilter: nf_tables: skip synchronize_rcu if transaction log is empty

After processing the transaction log, the remaining entries of the log
need to be released.

However, in some cases no entries remain, e.g. because the transaction
did not remove anything.
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_tables_api.c

@@ -5761,7 +5761,7 @@ static void nft_chain_commit_update(struct nft_trans *trans)
 	}
 }
 
-static void nf_tables_commit_release(struct nft_trans *trans)
+static void nft_commit_release(struct nft_trans *trans)
 {
 	switch (trans->msg_type) {
 	case NFT_MSG_DELTABLE:
@@ -5790,6 +5790,21 @@ static void nf_tables_commit_release(struct nft_trans *trans)
 	kfree(trans);
 }
 
+static void nf_tables_commit_release(struct net *net)
+{
+	struct nft_trans *trans, *next;
+
+	if (list_empty(&net->nft.commit_list))
+		return;
+
+	synchronize_rcu();
+
+	list_for_each_entry_safe(trans, next, &net->nft.commit_list, list) {
+		list_del(&trans->list);
+		nft_commit_release(trans);
+	}
+}
+
 static int nf_tables_commit(struct net *net, struct sk_buff *skb)
 {
 	struct nft_trans *trans, *next;
@@ -5920,13 +5935,7 @@ static int nf_tables_commit(struct net *net, struct sk_buff *skb)
 		}
 	}
 
-	synchronize_rcu();
-
-	list_for_each_entry_safe(trans, next, &net->nft.commit_list, list) {
-		list_del(&trans->list);
-		nf_tables_commit_release(trans);
-	}
-
+	nf_tables_commit_release(net);
 	nf_tables_gen_notify(net, skb, NFT_MSG_NEWGEN);
 
 	return 0;