ip6: insert route only when creating nexthop

When multiple packets arrive for the same on-link destination, only the
first packet that creates the nexthop should attempt route insertion.
Subsequent packets reuse the existing nexthop without trying to insert
a duplicate route.

This prevents EEXIST errors and packet drops during concurrent nexthop
resolution.

Signed-off-by: Anthony Harivel <aharivel@redhat.com>

Author: aharivel

modules/ip6/control/nexthop.c

@@ -59,6 +59,20 @@ void nh6_unreachable_cb(struct rte_mbuf *m) {
 					.ipv6 = *dst,
 				}
 			);
+			// Create an associated /128 route so that next packets take it
+			// in priority with a single route lookup.
+			int ret = rib6_insert(
+				nh->vrf_id,
+				nh->iface_id,
+				dst,
+				RTE_IPV6_MAX_DEPTH,
+				GR_NH_ORIGIN_INTERNAL,
+				remote
+			);
+			if (ret < 0) {
+				LOG(ERR, "failed to insert route: %s", strerror(errno));
+				goto free;
+			}
 		}
 
 		if (remote == NULL) {
@@ -69,20 +83,6 @@ void nh6_unreachable_cb(struct rte_mbuf *m) {
 		remote_l3 = nexthop_info_l3(remote);
 		assert(remote->iface_id == nh->iface_id);
 
-		// Create an associated /128 route so that next packets take it
-		// in priority with a single route lookup.
-		int ret = rib6_insert(
-			nh->vrf_id,
-			nh->iface_id,
-			dst,
-			RTE_IPV6_MAX_DEPTH,
-			GR_NH_ORIGIN_INTERNAL,
-			remote
-		);
-		if (ret < 0) {
-			LOG(ERR, "failed to insert route: %s", strerror(errno));
-			goto free;
-		}
 		nh = remote;
 		l3 = remote_l3;
 	}