diff --git a/include/net/kcm.h b/include/net/kcm.h
index 90279e5e09a5c0251aff6d1a72c5947bc55060f6..441e993be634ce58a450a923c7b5259736c1b21b 100644
--- a/include/net/kcm.h
+++ b/include/net/kcm.h
@@ -70,6 +70,7 @@ struct kcm_sock {
 	struct work_struct tx_work;
 	struct list_head wait_psock_list;
 	struct sk_buff *seq_skb;
+	struct mutex tx_mutex;
 	u32 tx_stopped : 1;
 
 	/* Don't use bit fields here, these are set under different locks */
diff --git a/net/kcm/kcmsock.c b/net/kcm/kcmsock.c
index 41d892bf12cc6a4d45a4dc0c23b447ff2809c518..829eb67240a998934e4877338122eb99ffe02d5f 100644
--- a/net/kcm/kcmsock.c
+++ b/net/kcm/kcmsock.c
@@ -754,6 +754,7 @@ static int kcm_sendmsg(struct socket *sock, struct msghdr *msg, size_t len)
 		  !(msg->msg_flags & MSG_MORE) : !!(msg->msg_flags & MSG_EOR);
 	int err = -EPIPE;
 
+	mutex_lock(&kcm->tx_mutex);
 	lock_sock(sk);
 
 	/* Per tcp_sendmsg this should be in poll */
@@ -925,6 +926,7 @@ static int kcm_sendmsg(struct socket *sock, struct msghdr *msg, size_t len)
 	KCM_STATS_ADD(kcm->stats.tx_bytes, copied);
 
 	release_sock(sk);
+	mutex_unlock(&kcm->tx_mutex);
 	return copied;
 
 out_error:
@@ -950,6 +952,7 @@ static int kcm_sendmsg(struct socket *sock, struct msghdr *msg, size_t len)
 		sk->sk_write_space(sk);
 
 	release_sock(sk);
+	mutex_unlock(&kcm->tx_mutex);
 	return err;
 }
 
@@ -1203,6 +1206,7 @@ static void init_kcm_sock(struct kcm_sock *kcm, struct kcm_mux *mux)
 	spin_unlock_bh(&mux->lock);
 
 	INIT_WORK(&kcm->tx_work, kcm_tx_work);
+	mutex_init(&kcm->tx_mutex);
 
 	spin_lock_bh(&mux->rx_lock);
 	kcm_rcv_ready(kcm);