[PATCH v1 2/2] SUNRPC: Capture completion of all RPC tasks

[Chuck Lever <chuck.lever@oracle.com>]

RPC tasks on the backchannel never invoke xprt_complete_rqst(), so
there is no way to report their tk_status at completion. Also, any
RPC task that exits via rpc_exit_task() before it is replied to will
also disappear without a trace.

Introduce a trace point that is symmetrical with rpc_task_begin that
captures the termination status of each RPC task.

Sample trace output for callback requests initiated on the server:
   kworker/u8:12-448   [003]   127.025240: rpc_task_end:         task:50@3 flags=ASYNC|DYNAMIC|SOFT|SOFTCONN|SENT runstate=RUNNING|ACTIVE status=0 action=rpc_exit_task
   kworker/u8:12-448   [002]   127.567310: rpc_task_end:         task:51@3 flags=ASYNC|DYNAMIC|SOFT|SOFTCONN|SENT runstate=RUNNING|ACTIVE status=0 action=rpc_exit_task
   kworker/u8:12-448   [001]   130.506817: rpc_task_end:         task:52@3 flags=ASYNC|DYNAMIC|SOFT|SOFTCONN|SENT runstate=RUNNING|ACTIVE status=0 action=rpc_exit_task

Odd, though, that I never see trace_rpc_task_complete, either in the
forward or backchannel. Should it be removed?

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 include/trace/events/sunrpc.h |    1 +
 net/sunrpc/sched.c            |    1 +
 2 files changed, 2 insertions(+)

diff --git a/include/trace/events/sunrpc.h b/include/trace/events/sunrpc.h
index c358a0af683b..9972823085ba 100644
--- a/include/trace/events/sunrpc.h
+++ b/include/trace/events/sunrpc.h
@@ -185,6 +185,7 @@
 DEFINE_RPC_RUNNING_EVENT(begin);
 DEFINE_RPC_RUNNING_EVENT(run_action);
 DEFINE_RPC_RUNNING_EVENT(complete);
+DEFINE_RPC_RUNNING_EVENT(end);
 
 DECLARE_EVENT_CLASS(rpc_task_queued,
 
diff --git a/net/sunrpc/sched.c b/net/sunrpc/sched.c
index 360afe153193..66a7a81504bf 100644
--- a/net/sunrpc/sched.c
+++ b/net/sunrpc/sched.c
@@ -824,6 +824,7 @@ void rpc_prepare_task(struct rpc_task *task)
  */
 void rpc_exit_task(struct rpc_task *task)
 {
+	trace_rpc_task_end(task, task->tk_action);
 	task->tk_action = NULL;
 	if (task->tk_ops->rpc_count_stats)
 		task->tk_ops->rpc_count_stats(task, task->tk_calldata);