When NBD calls sendmsg() and shutdown() for TCP sockets,
it must use lock_sock_try() to avoid potential deadlock.

While TCP already exports tcp_sendmsg_locked(), there is
no locked variant for inet_shutdown().

Let's add inet_shutdown_locked().

Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
---
 include/net/inet_common.h |  1 +
 net/ipv4/af_inet.c        | 43 +++++++++++++++++++++++++++++----------
 2 files changed, 33 insertions(+), 11 deletions(-)

diff --git a/include/net/inet_common.h b/include/net/inet_common.h
index 5dd2bf24449e..c085c39573c9 100644
--- a/include/net/inet_common.h
+++ b/include/net/inet_common.h
@@ -38,6 +38,7 @@ void inet_splice_eof(struct socket *sock);
 int inet_recvmsg(struct socket *sock, struct msghdr *msg, size_t size,
 		 int flags);
 int inet_shutdown(struct socket *sock, int how);
+int inet_shutdown_locked(struct socket *sock, int how);
 int inet_listen(struct socket *sock, int backlog);
 int __inet_listen_sk(struct sock *sk, int backlog);
 void inet_sock_destruct(struct sock *sk);
diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
index c7731e300a44..6fa8fd11fe6d 100644
--- a/net/ipv4/af_inet.c
+++ b/net/ipv4/af_inet.c
@@ -902,21 +902,11 @@ int inet_recvmsg(struct socket *sock, struct msghdr *msg, size_t size,
 }
 EXPORT_SYMBOL(inet_recvmsg);
 
-int inet_shutdown(struct socket *sock, int how)
+static int __inet_shutdown(struct socket *sock, int how)
 {
 	struct sock *sk = sock->sk;
 	int err = 0;
 
-	/* This should really check to make sure
-	 * the socket is a TCP socket. (WHY AC...)
-	 */
-	how++; /* maps 0->1 has the advantage of making bit 1 rcvs and
-		       1->2 bit 2 snds.
-		       2->3 */
-	if ((how & ~SHUTDOWN_MASK) || !how)	/* MAXINT->0 */
-		return -EINVAL;
-
-	lock_sock(sk);
 	if (sock->state == SS_CONNECTING) {
 		if ((1 << sk->sk_state) &
 		    (TCPF_SYN_SENT | TCPF_SYN_RECV | TCPF_CLOSE))
@@ -953,11 +943,42 @@ int inet_shutdown(struct socket *sock, int how)
 
 	/* Wake up anyone sleeping in poll. */
 	sk->sk_state_change(sk);
+
+	return err;
+}
+
+int inet_shutdown(struct socket *sock, int how)
+{
+	struct sock *sk = sock->sk;
+	int err;
+
+	/* maps SHUT_RD (0) -> RCV_SHUTDOWN (1), etc */
+	how++;
+
+	if ((how & ~SHUTDOWN_MASK) || !how)
+		return -EINVAL;
+
+	lock_sock(sk);
+	err = __inet_shutdown(sock, how);
 	release_sock(sk);
+
 	return err;
 }
 EXPORT_SYMBOL(inet_shutdown);
 
+int inet_shutdown_locked(struct socket *sock, int how)
+{
+	sock_owned_by_me(sock->sk);
+
+	how++;
+
+	if ((how & ~SHUTDOWN_MASK) || !how)
+		return -EINVAL;
+
+	return __inet_shutdown(sock, how);
+}
+EXPORT_SYMBOL_GPL(inet_shutdown_locked);
+
 /*
  *	ioctl() calls you can issue on an INET socket. Most of these are
  *	device configuration and stuff and very rarely used. Some ioctls
-- 
2.53.0.1018.g2bb0e51243-goog