SUNRPC: Ensure we always bump the backlog queue in xprt_free_slot

Whenever we free a slot, we know that the resulting xprt->num_reqs will
be less than xprt->max_reqs, so we know that we can release at least one
backlogged rpc_task.
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
Cc: stable@vger.kernel.org [>=3.1]

net/sunrpc/xprt.c

@@ -995,13 +995,11 @@ static void xprt_alloc_slot(struct rpc_task *task)
 
 static void xprt_free_slot(struct rpc_xprt *xprt, struct rpc_rqst *req)
 {
-	if (xprt_dynamic_free_slot(xprt, req))
-		return;
-
-	memset(req, 0, sizeof(*req));	/* mark unused */
-
 	spin_lock(&xprt->reserve_lock);
-	list_add(&req->rq_list, &xprt->free);
+	if (!xprt_dynamic_free_slot(xprt, req)) {
+		memset(req, 0, sizeof(*req));	/* mark unused */
+		list_add(&req->rq_list, &xprt->free);
+	}
 	rpc_wake_up_next(&xprt->backlog);
 	spin_unlock(&xprt->reserve_lock);
 }