cifs: Avoid umount hangs with smb2 when server is unresponsive

Do not send SMB2 Logoff command when reconnecting, the way smb1
code base works.

Also, no need to wait for a credit for an echo command when one is already
in flight.

Without these changes, umount command hangs if the server is unresponsive
e.g. hibernating.
Signed-off-by: Shirish Pargaonkar <shirishpargaonkar@gmail.com>
Acked-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <smfrench@us.ibm.com>

fs/cifs/smb2pdu.c

@@ -687,6 +687,10 @@ SMB2_logoff(const unsigned int xid, struct cifs_ses *ses)
 	else
 		return -EIO;
 
+	/* no need to send SMB logoff if uid already closed due to reconnect */
+	if (ses->need_reconnect)
+		goto smb2_session_already_dead;
+
 	rc = small_smb2_init(SMB2_LOGOFF, NULL, (void **) &req);
 	if (rc)
 		return rc;
@@ -701,6 +705,8 @@ SMB2_logoff(const unsigned int xid, struct cifs_ses *ses)
 	 * No tcon so can't do
 	 * cifs_stats_inc(&tcon->stats.smb2_stats.smb2_com_fail[SMB2...]);
 	 */
+
+smb2_session_already_dead:
 	return rc;
 }
 

fs/cifs/transport.c

@@ -410,8 +410,13 @@ static int
 wait_for_free_request(struct TCP_Server_Info *server, const int timeout,
 		      const int optype)
 {
-	return wait_for_free_credits(server, timeout,
-				server->ops->get_credits_field(server, optype));
+	int *val;
+
+	val = server->ops->get_credits_field(server, optype);
+	/* Since an echo is already inflight, no need to wait to send another */
+	if (*val <= 0 && optype == CIFS_ECHO_OP)
+		return -EAGAIN;
+	return wait_for_free_credits(server, timeout, val);
 }
 
 static int allocate_mid(struct cifs_ses *ses, struct smb_hdr *in_buf,