mds: fix race in connection accept; fix con replacement

We solve two problems with this patch.  The first is that the messenger
will now reuse an existing session's Connection with a new connection,
which means that we don't want to change session->connection when we
are validating an authorizer.  Instead, set (but do not change) it.

We also want to avoid a race where:

 - mds recovers, replays Sessions with no con's
 - multiple connection attempts for the same session race in the msgr
 - both are authorized, but out of order
 - Session->connection gets set to the losing attempt's Connection*

Instead, we take advantage of an accept event that is called only for
accepted winners.

Signed-off-by: Sage Weil <sage@inktank.com>

fixup

1 files changed, 1 insertions, 0 deletions

diff --git a/src/mds/MDS.h b/src/mds/MDS.h
index 67a51028d9c..0d7383b2d04 100644
--- a/src/mds/MDS.h
+++ b/src/mds/MDS.h
@@ -315,6 +315,7 @@ class MDS : public Dispatcher {
   bool ms_verify_authorizer(Connection *con, int peer_type,
 			       int protocol, bufferlist& authorizer_data, bufferlist& authorizer_reply,
 			       bool& isvalid);
+  void ms_handle_accept(Connection *con);
   void ms_handle_connect(Connection *con);
   bool ms_handle_reset(Connection *con);
   void ms_handle_remote_reset(Connection *con);