[PATCH] RPC: add a release_rqst callout to the RPC transport switch

 The final place where congestion control state is adjusted is in
 xprt_release, where each request is finally released.  Add a callout
 there to allow transports to perform additional processing when a
 request is about to be released.

 Test-plan:
 Use WAN simulation to cause sporadic bursty packet loss.  Look for significant
 regression in performance or client stability.

 Signed-off-by: Chuck Lever <cel@netapp.com>
 Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

include/linux/sunrpc/xprt.h

@@ -138,6 +138,7 @@ struct rpc_xprt_ops {
 	int		(*send_request)(struct rpc_task *task);
 	void		(*set_retrans_timeout)(struct rpc_task *task);
 	void		(*timer)(struct rpc_task *task);
+	void		(*release_request)(struct rpc_task *task);
 	void		(*close)(struct rpc_xprt *xprt);
 	void		(*destroy)(struct rpc_xprt *xprt);
 };
@@ -262,6 +263,7 @@ void			xprt_update_rtt(struct rpc_task *task);
 void			xprt_adjust_cwnd(struct rpc_task *task, int result);
 struct rpc_rqst *	xprt_lookup_rqst(struct rpc_xprt *xprt, u32 xid);
 void			xprt_complete_rqst(struct rpc_task *task, int copied);
+void			xprt_release_rqst_cong(struct rpc_task *task);
 void			xprt_disconnect(struct rpc_xprt *xprt);
 
 /*

net/sunrpc/xprt.c

@@ -289,6 +289,17 @@ __xprt_put_cong(struct rpc_xprt *xprt, struct rpc_rqst *req)
 	__xprt_lock_write_next_cong(xprt);
 }
 
+/**
+ * xprt_release_rqst_cong - housekeeping when request is complete
+ * @task: RPC request that recently completed
+ *
+ * Useful for transports that require congestion control.
+ */
+void xprt_release_rqst_cong(struct rpc_task *task)
+{
+	__xprt_put_cong(task->tk_xprt, task->tk_rqstp);
+}
+
 /**
  * xprt_adjust_cwnd - adjust transport congestion window
  * @task: recently completed RPC request used to adjust window
@@ -823,7 +834,8 @@ void xprt_release(struct rpc_task *task)
 		return;
 	spin_lock_bh(&xprt->transport_lock);
 	xprt->ops->release_xprt(xprt, task);
-	__xprt_put_cong(xprt, req);
+	if (xprt->ops->release_request)
+		xprt->ops->release_request(task);
 	if (!list_empty(&req->rq_list))
 		list_del(&req->rq_list);
 	xprt->last_used = jiffies;

net/sunrpc/xprtsock.c

@@ -1059,6 +1059,7 @@ static struct rpc_xprt_ops xs_udp_ops = {
 	.send_request		= xs_udp_send_request,
 	.set_retrans_timeout	= xprt_set_retrans_timeout_rtt,
 	.timer			= xs_udp_timer,
+	.release_request	= xprt_release_rqst_cong,
 	.close			= xs_close,
 	.destroy		= xs_destroy,
 };