rds: MP-RDS may use an invalid c_path

rds_sendmsg() calls rds_send_mprds_hash() to find a c_path to use to
send a message.  Suppose the RDS connection is not yet up.  In
rds_send_mprds_hash(), it does

	if (conn->c_npaths == 0)
		wait_event_interruptible(conn->c_hs_waitq,
					 (conn->c_npaths != 0));

If it is interrupted before the connection is set up,
rds_send_mprds_hash() will return a non-zero hash value.  Hence
rds_sendmsg() will use a non-zero c_path to send the message.  But if
the RDS connection ends up to be non-MP capable, the message will be
lost as only the zero c_path can be used.

Signed-off-by: Ka-Cheong Poon <ka-cheong.poon@oracle.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/rds/send.c b/net/rds/send.c
index acad04243b41dfab790e0418a0e635bec840cbea..94c7f74909be32f36344ab0b82cfad06c16b041f 100644 (file)
--- a/net/rds/send.c
+++ b/net/rds/send.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2006 Oracle.  All rights reserved.
+ * Copyright (c) 2006, 2018 Oracle and/or its affiliates. All rights reserved.
  *
  * This software is available to you under a choice of one of two
  * licenses.  You may choose to be licensed under the terms of the GNU
@@ -1017,10 +1017,15 @@ static int rds_send_mprds_hash(struct rds_sock *rs, struct rds_connection *conn)
        if (conn->c_npaths == 0 && hash != 0) {
                rds_send_ping(conn, 0);
 
-               if (conn->c_npaths == 0) {
-                       wait_event_interruptible(conn->c_hs_waitq,
-                                                (conn->c_npaths != 0));
-               }
+               /* The underlying connection is not up yet.  Need to wait
+                * until it is up to be sure that the non-zero c_path can be
+                * used.  But if we are interrupted, we have to use the zero
+                * c_path in case the connection ends up being non-MP capable.
+                */
+               if (conn->c_npaths == 0)
+                       if (wait_event_interruptible(conn->c_hs_waitq,
+                                                    conn->c_npaths != 0))
+                               hash = 0;
                if (conn->c_npaths == 1)
                        hash = 0;
        }