cifs: avoid races in parallel reconnects in smb1

Prevent multiple threads of doing negotiate, session setup and tree
connect by holding @ses->session_mutex in cifs_reconnect_tcon() while
reconnecting session and tcon.
Signed-off-by: Paulo Alcantara (SUSE) <pc@manguebit.com>
Reviewed-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/cifssmb.c

@@ -71,7 +71,7 @@ cifs_reconnect_tcon(struct cifs_tcon *tcon, int smb_command)
 	int rc;
 	struct cifs_ses *ses;
 	struct TCP_Server_Info *server;
-	struct nls_table *nls_codepage;
+	struct nls_table *nls_codepage = NULL;
 
 	/*
 	 * SMBs NegProt, SessSetup, uLogoff do not have tcon yet so check for
@@ -99,6 +99,7 @@ cifs_reconnect_tcon(struct cifs_tcon *tcon, int smb_command)
 	}
 	spin_unlock(&tcon->tc_lock);
 
+again:
 	rc = cifs_wait_for_server_reconnect(server, tcon->retry);
 	if (rc)
 		return rc;
@@ -110,8 +111,7 @@ cifs_reconnect_tcon(struct cifs_tcon *tcon, int smb_command)
 	}
 	spin_unlock(&ses->chan_lock);
 
-	nls_codepage = load_nls_default();
-
+	mutex_lock(&ses->session_mutex);
 	/*
 	 * Recheck after acquire mutex. If another thread is negotiating
 	 * and the server never sends an answer the socket will be closed
@@ -120,29 +120,38 @@ cifs_reconnect_tcon(struct cifs_tcon *tcon, int smb_command)
 	spin_lock(&server->srv_lock);
 	if (server->tcpStatus == CifsNeedReconnect) {
 		spin_unlock(&server->srv_lock);
+		mutex_lock(&ses->session_mutex);
+
+		if (tcon->retry)
+			goto again;
 		rc = -EHOSTDOWN;
 		goto out;
 	}
 	spin_unlock(&server->srv_lock);
 
+	nls_codepage = load_nls_default();
+
 	/*
 	 * need to prevent multiple threads trying to simultaneously
 	 * reconnect the same SMB session
 	 */
+	spin_lock(&ses->ses_lock);
 	spin_lock(&ses->chan_lock);
-	if (!cifs_chan_needs_reconnect(ses, server)) {
+	if (!cifs_chan_needs_reconnect(ses, server) &&
+	    ses->ses_status == SES_GOOD) {
 		spin_unlock(&ses->chan_lock);
+		spin_unlock(&ses->ses_lock);
 
 		/* this means that we only need to tree connect */
 		if (tcon->need_reconnect)
 			goto skip_sess_setup;
 
-		rc = -EHOSTDOWN;
+		mutex_unlock(&ses->session_mutex);
 		goto out;
 	}
 	spin_unlock(&ses->chan_lock);
+	spin_unlock(&ses->ses_lock);
 
-	mutex_lock(&ses->session_mutex);
 	rc = cifs_negotiate_protocol(0, ses, server);
 	if (!rc)
 		rc = cifs_setup_session(0, ses, server, nls_codepage);