diff --git a/include/net/route.h b/include/net/route.h
index f90106f383c5..45290177a33c 100644
--- a/include/net/route.h
+++ b/include/net/route.h
@@ -276,6 +276,8 @@ int fib_dump_info_fnhe(struct sk_buff *skb, struct netlink_callback *cb,
 		       u32 table_id, struct fib_info *fi,
 		       int *fa_index, int fa_start, unsigned int flags);
 
+void fnhe_update_pmtu(struct fib_nh_exception *fnhe, u32 new, u32 orig);
+
 static inline void ip_rt_put(struct rtable *rt)
 {
 	/* dst_release() accepts a NULL parameter.
diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
index 78f84ae3ee12..0483519b7fb0 100644
--- a/net/ipv4/fib_semantics.c
+++ b/net/ipv4/fib_semantics.c
@@ -1895,42 +1895,30 @@ static int call_fib_nh_notifiers(struct fib_nh *nh,
 	return NOTIFY_DONE;
 }
 
-/* Update the PMTU of exceptions when:
- * - the new MTU of the first hop becomes smaller than the PMTU
- * - the old MTU was the same as the PMTU, and it limited discovery of
- *   larger MTUs on the path. With that limit raised, we can now
- *   discover larger MTUs
- * A special case is locked exceptions, for which the PMTU is smaller
- * than the minimal accepted PMTU:
- * - if the new MTU is greater than the PMTU, don't make any change
- * - otherwise, unlock and set PMTU
+/* Walk the exceptions of a nexthop after its first hop MTU changed. The
+ * chain is RCU protected here, while fnhe_update_pmtu() takes fnhe_lock
+ * for the update of each entry.
  */
 void fib_nhc_update_mtu(struct fib_nh_common *nhc, u32 new, u32 orig)
 {
 	struct fnhe_hash_bucket *bucket;
 	int i;
 
-	bucket = rcu_dereference_protected(nhc->nhc_exceptions, 1);
+	rcu_read_lock();
+	bucket = rcu_dereference(nhc->nhc_exceptions);
 	if (!bucket)
-		return;
+		goto out;
 
 	for (i = 0; i < FNHE_HASH_SIZE; i++) {
 		struct fib_nh_exception *fnhe;
 
-		for (fnhe = rcu_dereference_protected(bucket[i].chain, 1);
+		for (fnhe = rcu_dereference(bucket[i].chain);
 		     fnhe;
-		     fnhe = rcu_dereference_protected(fnhe->fnhe_next, 1)) {
-			if (fnhe->fnhe_mtu_locked) {
-				if (new <= fnhe->fnhe_pmtu) {
-					fnhe->fnhe_pmtu = new;
-					fnhe->fnhe_mtu_locked = false;
-				}
-			} else if (new < fnhe->fnhe_pmtu ||
-				   orig == fnhe->fnhe_pmtu) {
-				fnhe->fnhe_pmtu = new;
-			}
-		}
+		     fnhe = rcu_dereference(fnhe->fnhe_next))
+			fnhe_update_pmtu(fnhe, new, orig);
 	}
+out:
+	rcu_read_unlock();
 }
 
 void fib_sync_mtu(struct net_device *dev, u32 orig_mtu)
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 152d8cb28f65..b82401a6baed 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -741,6 +741,35 @@ static void update_or_create_fnhe(struct fib_nh_common *nhc, __be32 daddr,
 	spin_unlock_bh(&fnhe_lock);
 }
 
+/* Update the PMTU of an exception when:
+ * - the new MTU of the first hop becomes smaller than the PMTU
+ * - the old MTU was the same as the PMTU, and it limited discovery of
+ *   larger MTUs on the path. With that limit raised, we can now
+ *   discover larger MTUs
+ * A special case is locked exceptions, for which the PMTU is smaller
+ * than the minimal accepted PMTU:
+ * - if the new MTU is greater than the PMTU, don't make any change
+ * - otherwise, unlock and set PMTU
+ *
+ * fnhe_lock keeps fnhe_pmtu and fnhe_mtu_locked consistent against
+ * update_or_create_fnhe(), which sets both under the same lock.
+ */
+void fnhe_update_pmtu(struct fib_nh_exception *fnhe, u32 new, u32 orig)
+{
+	spin_lock_bh(&fnhe_lock);
+
+	if (fnhe->fnhe_mtu_locked) {
+		if (new <= fnhe->fnhe_pmtu) {
+			fnhe->fnhe_pmtu = new;
+			fnhe->fnhe_mtu_locked = false;
+		}
+	} else if (new < fnhe->fnhe_pmtu || orig == fnhe->fnhe_pmtu) {
+		fnhe->fnhe_pmtu = new;
+	}
+
+	spin_unlock_bh(&fnhe_lock);
+}
+
 static void __ip_do_redirect(struct rtable *rt, struct sk_buff *skb, struct flowi4 *fl4,
 			     bool kill_route)
 {