smb: client: fix hang in wait_for_response() for negproto

Call cifs_reconnect() to wake up processes waiting on negotiate
protocol to handle the case where server abruptly shut down and had no
chance to properly close the socket.

Simple reproducer:

  ssh 192.168.2.100 pkill -STOP smbd
  mount.cifs //192.168.2.100/test /mnt -o ... [never returns]

Cc: Rickard Andersson <rickaran@axis.com>
Signed-off-by: Paulo Alcantara (Red Hat) <pc@manguebit.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/smb/client/connect.c

@@ -656,6 +656,19 @@ allocate_buffers(struct TCP_Server_Info *server)
 static bool
 server_unresponsive(struct TCP_Server_Info *server)
 {
+	/*
+	 * If we're in the process of mounting a share or reconnecting a session
+	 * and the server abruptly shut down (e.g. socket wasn't closed, packet
+	 * had been ACK'ed but no SMB response), don't wait longer than 20s to
+	 * negotiate protocol.
+	 */
+	spin_lock(&server->srv_lock);
+	if (server->tcpStatus == CifsInNegotiate &&
+	    time_after(jiffies, server->lstrp + 20 * HZ)) {
+		spin_unlock(&server->srv_lock);
+		cifs_reconnect(server, false);
+		return true;
+	}
 	/*
 	 * We need to wait 3 echo intervals to make sure we handle such
 	 * situations right:
@@ -667,7 +680,6 @@ server_unresponsive(struct TCP_Server_Info *server)
 	 * 65s kernel_recvmsg times out, and we see that we haven't gotten
 	 *     a response in >60s.
 	 */
-	spin_lock(&server->srv_lock);
 	if ((server->tcpStatus == CifsGood ||
 	    server->tcpStatus == CifsNeedNegotiate) &&
 	    (!server->ops->can_echo || server->ops->can_echo(server)) &&