diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index cf0923579af4..9ef20389622d 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -1881,6 +1881,11 @@ struct net_device {
 	unsigned char		if_port;
 	unsigned char		dma;
 
+	/* Note : dev->mtu is often read without holding a lock.
+	 * Writers usually hold RTNL.
+	 * It is recommended to use READ_ONCE() to annotate the reads,
+	 * and to use WRITE_ONCE() to annotate the writes.
+	 */
 	unsigned int		mtu;
 	unsigned int		min_mtu;
 	unsigned int		max_mtu;
diff --git a/include/net/ip.h b/include/net/ip.h
index 02d68e346f67..5b317c9f4470 100644
--- a/include/net/ip.h
+++ b/include/net/ip.h
@@ -760,4 +760,9 @@ int ip_misc_proc_init(void);
 int rtm_getroute_parse_ip_proto(struct nlattr *attr, u8 *ip_proto, u8 family,
 				struct netlink_ext_ack *extack);
 
+static inline bool inetdev_valid_mtu(unsigned int mtu)
+{
+	return likely(mtu >= IPV4_MIN_MTU);
+}
+
 #endif	/* _IP_H */
diff --git a/net/core/dev.c b/net/core/dev.c
index e7c027fb4808..2c277b8aba38 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -8188,7 +8188,8 @@ int __dev_set_mtu(struct net_device *dev, int new_mtu)
 	if (ops->ndo_change_mtu)
 		return ops->ndo_change_mtu(dev, new_mtu);
 
-	dev->mtu = new_mtu;
+	/* Pairs with all the lockless reads of dev->mtu in the stack */
+	WRITE_ONCE(dev->mtu, new_mtu);
 	return 0;
 }
 EXPORT_SYMBOL(__dev_set_mtu);
diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
index a4b5bd4d2c89..e4632bd2026d 100644
--- a/net/ipv4/devinet.c
+++ b/net/ipv4/devinet.c
@@ -1496,11 +1496,6 @@ static void inetdev_changename(struct net_device *dev, struct in_device *in_dev)
 	}
 }
 
-static bool inetdev_valid_mtu(unsigned int mtu)
-{
-	return mtu >= IPV4_MIN_MTU;
-}
-
 static void inetdev_send_gratuitous_arp(struct net_device *dev,
 					struct in_device *in_dev)
 
diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index 9d83cb320dcb..14db1e0b8a6e 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -1258,15 +1258,18 @@ static int ip_setup_cork(struct sock *sk, struct inet_cork *cork,
 		cork->addr = ipc->addr;
 	}
 
-	/*
-	 * We steal reference to this route, caller should not release it
-	 */
-	*rtp = NULL;
 	cork->fragsize = ip_sk_use_pmtu(sk) ?
-			 dst_mtu(&rt->dst) : rt->dst.dev->mtu;
+			 dst_mtu(&rt->dst) : READ_ONCE(rt->dst.dev->mtu);
+
+	if (!inetdev_valid_mtu(cork->fragsize))
+		return -ENETUNREACH;
 
 	cork->gso_size = ipc->gso_size;
+
 	cork->dst = &rt->dst;
+	/* We stole this route, caller should not release it. */
+	*rtp = NULL;
+
 	cork->length = 0;
 	cork->ttl = ipc->ttl;
 	cork->tos = ipc->tos;