workqueue: add worker function to workqueue_execute_end tracepoint

It's surprising that workqueue_execute_end includes only the work when
its counterpart workqueue_execute_start has both the work and the worker
function.

You can't set a tracing filter or trigger based on the function, and
postprocessing scripts interested in specific functions are harder to
write since they have to remember the work from _start and match it up
with the same field in _end.

Add the function name, taking care to use the copy stashed in the
worker since the work is no longer safe to touch.

Signed-off-by: Daniel Jordan <daniel.m.jordan@oracle.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Tejun Heo <tj@kernel.org>

include/trace/events/workqueue.h

@@ -108,14 +108,27 @@ TRACE_EVENT(workqueue_execute_start,
 /**
  * workqueue_execute_end - called immediately after the workqueue callback
  * @work:	pointer to struct work_struct
+ * @function:   pointer to worker function
  *
  * Allows to track workqueue execution.
  */
-DEFINE_EVENT(workqueue_work, workqueue_execute_end,
+TRACE_EVENT(workqueue_execute_end,
 
-	TP_PROTO(struct work_struct *work),
+	TP_PROTO(struct work_struct *work, work_func_t function),
 
-	TP_ARGS(work)
+	TP_ARGS(work, function),
+
+	TP_STRUCT__entry(
+		__field( void *,	work	)
+		__field( void *,	function)
+	),
+
+	TP_fast_assign(
+		__entry->work		= work;
+		__entry->function	= function;
+	),
+
+	TP_printk("work struct %p: function %ps", __entry->work, __entry->function)
 );
 
 #endif /*  _TRACE_WORKQUEUE_H */

kernel/workqueue.c

@@ -2266,7 +2266,7 @@ __acquires(&pool->lock)
 	 * While we must be careful to not use "work" after this, the trace
 	 * point will only record its address.
 	 */
-	trace_workqueue_execute_end(work);
+	trace_workqueue_execute_end(work, worker->current_func);
 	lock_map_release(&lockdep_map);
 	lock_map_release(&pwq->wq->lockdep_map);