nbd: don't shutdown sock with irq's disabled

BugLink: https://bugs.launchpad.net/bugs/1793464

We hit a warning when shutting down the nbd connection because we have irq's
disabled.  We don't really need to do the shutdown under the lock, just clear
the nbd->sock.  So do the shutdown outside of the irq.  This gets rid of the
warning.
Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
(backported from commit c2611898)
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Kleber Souza <kleber.souza@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

drivers/block/nbd.c

@@ -172,6 +172,8 @@ static void nbd_end_request(struct nbd_device *nbd, struct request *req)
  */
 static void sock_shutdown(struct nbd_device *nbd)
 {
+	struct socket *sock;
+
 	spin_lock_irq(&nbd->sock_lock);
 
 	if (!nbd->sock) {
@@ -179,18 +181,21 @@ static void sock_shutdown(struct nbd_device *nbd)
 		return;
 	}
 
+	sock = nbd->sock;
 	dev_warn(disk_to_dev(nbd->disk), "shutting down socket\n");
-	kernel_sock_shutdown(nbd->sock, SHUT_RDWR);
-	sockfd_put(nbd->sock);
 	nbd->sock = NULL;
 	spin_unlock_irq(&nbd->sock_lock);
 
+	kernel_sock_shutdown(sock, SHUT_RDWR);
+	sockfd_put(sock);
+
 	del_timer(&nbd->timeout_timer);
 }
 
 static void nbd_xmit_timeout(unsigned long arg)
 {
 	struct nbd_device *nbd = (struct nbd_device *)arg;
+	struct socket *sock = NULL;
 	unsigned long flags;
 
 	if (list_empty(&nbd->queue_head))
@@ -200,10 +205,16 @@ static void nbd_xmit_timeout(unsigned long arg)
 
 	nbd->timedout = true;
 
-	if (nbd->sock)
-		kernel_sock_shutdown(nbd->sock, SHUT_RDWR);
+	if (nbd->sock) {
+		sock = nbd->sock;
+		get_file(sock->file);
+	}
 
 	spin_unlock_irqrestore(&nbd->sock_lock, flags);
+	if (sock) {
+		kernel_sock_shutdown(sock, SHUT_RDWR);
+		sockfd_put(sock);
+	}
 
 	dev_err(nbd_to_dev(nbd), "Connection timed out, shutting down connection\n");
 }