diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index c7861e4..d837dad 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -2458,6 +2458,13 @@
 	struct netlink_ext_ack	*extack;
 };
 
+struct netdev_notifier_info_ext {
+	struct netdev_notifier_info info; /* must be first */
+	union {
+		u32 mtu;
+	} ext;
+};
+
 struct netdev_notifier_change_info {
 	struct netdev_notifier_info info; /* must be first */
 	unsigned int flags_changed;
diff --git a/include/net/ip_fib.h b/include/net/ip_fib.h
index 69c91d1..c9b7b13 100644
--- a/include/net/ip_fib.h
+++ b/include/net/ip_fib.h
@@ -394,6 +394,7 @@
 int fib_sync_down_dev(struct net_device *dev, unsigned long event, bool force);
 int fib_sync_down_addr(struct net_device *dev, __be32 local);
 int fib_sync_up(struct net_device *dev, unsigned int nh_flags);
+void fib_sync_mtu(struct net_device *dev, u32 orig_mtu);
 
 #ifdef CONFIG_IP_ROUTE_MULTIPATH
 int fib_multipath_hash(const struct net *net, const struct flowi4 *fl4,
diff --git a/net/core/dev.c b/net/core/dev.c
index 82114e1..93243479 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1752,6 +1752,28 @@
 }
 EXPORT_SYMBOL(call_netdevice_notifiers);
 
+/**
+ *	call_netdevice_notifiers_mtu - call all network notifier blocks
+ *	@val: value passed unmodified to notifier function
+ *	@dev: net_device pointer passed unmodified to notifier function
+ *	@arg: additional u32 argument passed to the notifier function
+ *
+ *	Call all network notifier blocks.  Parameters and return value
+ *	are as for raw_notifier_call_chain().
+ */
+static int call_netdevice_notifiers_mtu(unsigned long val,
+					struct net_device *dev, u32 arg)
+{
+	struct netdev_notifier_info_ext info = {
+		.info.dev = dev,
+		.ext.mtu = arg,
+	};
+
+	BUILD_BUG_ON(offsetof(struct netdev_notifier_info_ext, info) != 0);
+
+	return call_netdevice_notifiers_info(val, &info.info);
+}
+
 #ifdef CONFIG_NET_INGRESS
 static DEFINE_STATIC_KEY_FALSE(ingress_needed_key);
 
@@ -7574,14 +7596,16 @@
 	err = __dev_set_mtu(dev, new_mtu);
 
 	if (!err) {
-		err = call_netdevice_notifiers(NETDEV_CHANGEMTU, dev);
+		err = call_netdevice_notifiers_mtu(NETDEV_CHANGEMTU, dev,
+						   orig_mtu);
 		err = notifier_to_errno(err);
 		if (err) {
 			/* setting mtu back and notifying everyone again,
 			 * so that they have a chance to revert changes.
 			 */
 			__dev_set_mtu(dev, orig_mtu);
-			call_netdevice_notifiers(NETDEV_CHANGEMTU, dev);
+			call_netdevice_notifiers_mtu(NETDEV_CHANGEMTU, dev,
+						     new_mtu);
 		}
 	}
 	return err;
diff --git a/net/ipv4/fib_frontend.c b/net/ipv4/fib_frontend.c
index 2998b0e..0113993 100644
--- a/net/ipv4/fib_frontend.c
+++ b/net/ipv4/fib_frontend.c
@@ -1243,7 +1243,8 @@
 static int fib_netdev_event(struct notifier_block *this, unsigned long event, void *ptr)
 {
 	struct net_device *dev = netdev_notifier_info_to_dev(ptr);
-	struct netdev_notifier_changeupper_info *info;
+	struct netdev_notifier_changeupper_info *upper_info = ptr;
+	struct netdev_notifier_info_ext *info_ext = ptr;
 	struct in_device *in_dev;
 	struct net *net = dev_net(dev);
 	unsigned int flags;
@@ -1278,16 +1279,19 @@
 			fib_sync_up(dev, RTNH_F_LINKDOWN);
 		else
 			fib_sync_down_dev(dev, event, false);
-		/* fall through */
+		rt_cache_flush(net);
+		break;
 	case NETDEV_CHANGEMTU:
+		fib_sync_mtu(dev, info_ext->ext.mtu);
 		rt_cache_flush(net);
 		break;
 	case NETDEV_CHANGEUPPER:
-		info = ptr;
+		upper_info = ptr;
 		/* flush all routes if dev is linked to or unlinked from
 		 * an L3 master device (e.g., VRF)
 		 */
-		if (info->upper_dev && netif_is_l3_master(info->upper_dev))
+		if (upper_info->upper_dev &&
+		    netif_is_l3_master(upper_info->upper_dev))
 			fib_disable_ip(dev, NETDEV_DOWN, true);
 		break;
 	}
diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
index f3c89cc..446204c 100644
--- a/net/ipv4/fib_semantics.c
+++ b/net/ipv4/fib_semantics.c
@@ -1470,6 +1470,56 @@
 	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
+ */
+static void nh_update_mtu(struct fib_nh *nh, u32 new, u32 orig)
+{
+	struct fnhe_hash_bucket *bucket;
+	int i;
+
+	bucket = rcu_dereference_protected(nh->nh_exceptions, 1);
+	if (!bucket)
+		return;
+
+	for (i = 0; i < FNHE_HASH_SIZE; i++) {
+		struct fib_nh_exception *fnhe;
+
+		for (fnhe = rcu_dereference_protected(bucket[i].chain, 1);
+		     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;
+			}
+		}
+	}
+}
+
+void fib_sync_mtu(struct net_device *dev, u32 orig_mtu)
+{
+	unsigned int hash = fib_devindex_hashfn(dev->ifindex);
+	struct hlist_head *head = &fib_info_devhash[hash];
+	struct fib_nh *nh;
+
+	hlist_for_each_entry(nh, head, nh_hash) {
+		if (nh->nh_dev == dev)
+			nh_update_mtu(nh, dev->mtu, orig_mtu);
+	}
+}
+
 /* Event              force Flags           Description
  * NETDEV_CHANGE      0     LINKDOWN        Carrier OFF, not for scope host
  * NETDEV_DOWN        0     LINKDOWN|DEAD   Link down, not for scope host
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index b678466..8501554 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -1001,21 +1001,22 @@
 static void __ip_rt_update_pmtu(struct rtable *rt, struct flowi4 *fl4, u32 mtu)
 {
 	struct dst_entry *dst = &rt->dst;
+	u32 old_mtu = ipv4_mtu(dst);
 	struct fib_result res;
 	bool lock = false;
 
 	if (ip_mtu_locked(dst))
 		return;
 
-	if (ipv4_mtu(dst) < mtu)
+	if (old_mtu < mtu)
 		return;
 
 	if (mtu < ip_rt_min_pmtu) {
 		lock = true;
-		mtu = ip_rt_min_pmtu;
+		mtu = min(old_mtu, ip_rt_min_pmtu);
 	}
 
-	if (rt->rt_pmtu == mtu &&
+	if (rt->rt_pmtu == mtu && !lock &&
 	    time_before(jiffies, dst->expires - ip_rt_mtu_expires / 2))
 		return;