tracing: Use refcount for trace_event_file reference counter

Instead of using an atomic counter for the trace_event_file reference
counter, use the refcount interface. It has various checks to make sure
the reference counting is correct, and will warn if it detects an error
(like refcount_inc() on '0').

Cc: Mathieu Desnoyers <[e-mail]>
Link: https://lore.kernel.org/[e-mail]
Acked-by: Masami Hiramatsu (Google) <[e-mail]>
Signed-off-by: Steven Rostedt (Google) <[e-mail]>

include/linux/trace_events.h

···
 	 * caching and such. Which is mostly OK ;-)
 	 */
 	unsigned long		flags;
-	atomic_t		ref;	/* ref count for opened files */
+	refcount_t		ref;	/* ref count for opened files */
 	atomic_t		sm_ref;	/* soft-mode reference counter */
 	atomic_t		tm_ref;	/* trigger-mode reference counter */
 };

kernel/trace/trace_events.c

···
 
 void event_file_get(struct trace_event_file *file)
 {
-	atomic_inc(&file->ref);
+	refcount_inc(&file->ref);
 }
 
 void event_file_put(struct trace_event_file *file)
 {
-	if (WARN_ON_ONCE(!atomic_read(&file->ref))) {
+	if (WARN_ON_ONCE(!refcount_read(&file->ref))) {
 		if (file->flags & EVENT_FILE_FL_FREED)
 			kmem_cache_free(file_cachep, file);
 		return;
 	}
 
-	if (atomic_dec_and_test(&file->ref)) {
+	if (refcount_dec_and_test(&file->ref)) {
 		/* Count should only go to zero when it is freed */
 		if (WARN_ON_ONCE(!(file->flags & EVENT_FILE_FL_FREED)))
 			return;
···
 	atomic_set(&file->tm_ref, 0);
 	INIT_LIST_HEAD(&file->triggers);
 	list_add(&file->list, &tr->events);
-	event_file_get(file);
+	refcount_set(&file->ref, 1);
 
 	return file;
 }