mpls_route_input_rcu() is called from mpls_forward() and
mpls_getroute().

The former is under RCU, and the latter is under RTNL, so
mpls_route_input_rcu() uses rcu_dereference_rtnl().

Let's use rcu_dereference() in mpls_route_input_rcu() and
add an RTNL variant for mpls_getroute().

Later, we will remove rtnl_dereference() there.

Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
---
 net/mpls/af_mpls.c | 28 ++++++++++++++++++----------
 1 file changed, 18 insertions(+), 10 deletions(-)

diff --git a/net/mpls/af_mpls.c b/net/mpls/af_mpls.c
index a715b12860e9..530f7e6f7b3c 100644
--- a/net/mpls/af_mpls.c
+++ b/net/mpls/af_mpls.c
@@ -75,16 +75,23 @@ static void rtmsg_lfib(int event, u32 label, struct mpls_route *rt,
 		       struct nlmsghdr *nlh, struct net *net, u32 portid,
 		       unsigned int nlm_flags);
 
-static struct mpls_route *mpls_route_input_rcu(struct net *net, unsigned index)
+static struct mpls_route *mpls_route_input(struct net *net, unsigned int index)
 {
-	struct mpls_route *rt = NULL;
+	struct mpls_route __rcu **platform_label;
 
-	if (index < net->mpls.platform_labels) {
-		struct mpls_route __rcu **platform_label =
-			rcu_dereference_rtnl(net->mpls.platform_label);
-		rt = rcu_dereference_rtnl(platform_label[index]);
-	}
-	return rt;
+	platform_label = rtnl_dereference(net->mpls.platform_label);
+	return rtnl_dereference(platform_label[index]);
+}
+
+static struct mpls_route *mpls_route_input_rcu(struct net *net, unsigned int index)
+{
+	struct mpls_route __rcu **platform_label;
+
+	if (index >= net->mpls.platform_labels)
+		return NULL;
+
+	platform_label = rcu_dereference(net->mpls.platform_label);
+	return rcu_dereference(platform_label[index]);
 }
 
 bool mpls_output_possible(const struct net_device *dev)
@@ -2373,12 +2380,12 @@ static int mpls_getroute(struct sk_buff *in_skb, struct nlmsghdr *in_nlh,
 	u32 portid = NETLINK_CB(in_skb).portid;
 	u32 in_label = LABEL_NOT_SPECIFIED;
 	struct nlattr *tb[RTA_MAX + 1];
+	struct mpls_route *rt = NULL;
 	u32 labels[MAX_NEW_LABELS];
 	struct mpls_shim_hdr *hdr;
 	unsigned int hdr_size = 0;
 	const struct mpls_nh *nh;
 	struct net_device *dev;
-	struct mpls_route *rt;
 	struct rtmsg *rtm, *r;
 	struct nlmsghdr *nlh;
 	struct sk_buff *skb;
@@ -2406,7 +2413,8 @@ static int mpls_getroute(struct sk_buff *in_skb, struct nlmsghdr *in_nlh,
 		}
 	}
 
-	rt = mpls_route_input_rcu(net, in_label);
+	if (in_label < net->mpls.platform_labels)
+		rt = mpls_route_input(net, in_label);
 	if (!rt) {
 		err = -ENETUNREACH;
 		goto errout;
-- 
2.51.1.851.g4ebd6896fd-goog