rpc: keep backchannel xprt as long as server connection

Multiple backchannels can share the same tcp connection; from rfc 5661 section
2.10.3.1:

	A connection's association with a session is not exclusive.  A
	connection associated with the channel(s) of one session may be
	simultaneously associated with the channel(s) of other sessions
	including sessions associated with other client IDs.

However, multiple backchannels share a connection, they must all share
the same xid stream (hence the same rpc_xprt); the only way we have to
match replies with calls at the rpc layer is using the xid.

So, keep the rpc_xprt around as long as the connection lasts, in case
we're asked to use the connection as a backchannel again.

Requests to create new backchannel clients over a given server
connection should results in creating new clients that reuse the
existing rpc_xprt.

But to start, just reject attempts to associate multiple rpc_xprt's with
the same underlying bc_xprt.

Signed-off-by: J. Bruce Fields <bfields@redhat.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c
index 4c8f18aff7c3..749ad15ae305 100644
--- a/net/sunrpc/xprt.c
+++ b/net/sunrpc/xprt.c
@@ -965,6 +965,7 @@ struct rpc_xprt *xprt_alloc(struct net *net, int size, int max_req)
         xprt = kzalloc(size, GFP_KERNEL);
         if (xprt == NULL)
                 goto out;
+        kref_init(&xprt->kref);
 
         xprt->max_reqs = max_req;
         xprt->slot = kcalloc(max_req, sizeof(struct rpc_rqst), GFP_KERNEL);
@@ -1102,7 +1103,6 @@ found:
                 return xprt;
         }
 
-        kref_init(&xprt->kref);
         spin_lock_init(&xprt->transport_lock);
         spin_lock_init(&xprt->reserve_lock);