diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 29ed5977ac04..81c85ba6e2b8 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -1730,6 +1730,11 @@ 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 short		type;
 	unsigned short		hard_header_len;
diff --git a/include/net/ip.h b/include/net/ip.h
index a3c1b9dfc9a1..d577fb5647c5 100644
--- a/include/net/ip.h
+++ b/include/net/ip.h
@@ -620,4 +620,9 @@ extern int sysctl_icmp_msgs_burst;
 int ip_misc_proc_init(void);
 #endif
 
+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 c6fb7e61cb40..842654302110 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -6584,7 +6584,8 @@ static 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;
 }
 
diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
index 93438113d136..6c873cb829ca 100644
--- a/net/ipv4/devinet.c
+++ b/net/ipv4/devinet.c
@@ -1386,11 +1386,6 @@ skip:
 	}
 }
 
-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 7f1a85c6a614..4f3decbe6a3a 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -1159,13 +1159,17 @@ static int ip_setup_cork(struct sock *sk, struct inet_cork *cork,
 	rt = *rtp;
 	if (unlikely(!rt))
 		return -EFAULT;
-	/*
-	 * 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->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;