xprtrdma: Destroy rpcrdma_rep when Receive is flushed

This reduces the hardware and memory footprint of an unconnected
transport.

At some point in the future, transport reconnect will allow
resolving the destination IP address through a different device. The
current change enables reps for the new connection to be allocated
on whichever NUMA node the new device affines to after a reconnect.

Note that this does not destroy _all_ the transport's reps... there
will be a few that are still part of a running RPC completion.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

net/sunrpc/xprtrdma/verbs.c

@@ -80,6 +80,7 @@ static void rpcrdma_sendctx_put_locked(struct rpcrdma_xprt *r_xprt,
 				       struct rpcrdma_sendctx *sc);
 static int rpcrdma_reqs_setup(struct rpcrdma_xprt *r_xprt);
 static void rpcrdma_reqs_reset(struct rpcrdma_xprt *r_xprt);
+static void rpcrdma_rep_destroy(struct rpcrdma_rep *rep);
 static void rpcrdma_reps_unmap(struct rpcrdma_xprt *r_xprt);
 static void rpcrdma_mrs_create(struct rpcrdma_xprt *r_xprt);
 static void rpcrdma_mrs_destroy(struct rpcrdma_xprt *r_xprt);
@@ -177,7 +178,7 @@ rpcrdma_wc_receive(struct ib_cq *cq, struct ib_wc *wc)
 	return;
 
 out_flushed:
-	rpcrdma_recv_buffer_put(rep);
+	rpcrdma_rep_destroy(rep);
 }
 
 static void rpcrdma_update_cm_private(struct rpcrdma_xprt *r_xprt,
@@ -1106,6 +1107,9 @@ static void rpcrdma_reqs_reset(struct rpcrdma_xprt *r_xprt)
 		rpcrdma_req_reset(req);
 }
 
+/* No locking needed here. This function is called only by the
+ * Receive completion handler.
+ */
 static struct rpcrdma_rep *rpcrdma_rep_create(struct rpcrdma_xprt *r_xprt,
 					      bool temp)
 {
@@ -1138,6 +1142,9 @@ static struct rpcrdma_rep *rpcrdma_rep_create(struct rpcrdma_xprt *r_xprt,
 	return NULL;
 }
 
+/* No locking needed here. This function is invoked only by the
+ * Receive completion handler, or during transport shutdown.
+ */
 static void rpcrdma_rep_destroy(struct rpcrdma_rep *rep)
 {
 	list_del(&rep->rr_all);