tracing: Have dynamic events have a ref counter

As dynamic events are not created by modules, if something is attached to
one, calling "try_module_get()" on its "mod" field, is not going to keep
the dynamic event from going away.

Since dynamic events do not need the "mod" pointer of the event structure,
make a union out of it in order to save memory (there's one structure for
each of the thousand+ events in the kernel), and have any event with the
DYNAMIC flag set to use a ref counter instead.

Link: https://lore.kernel.org/linux-trace-devel/20210813004448.51c7de69ce432d338f4d226b@kernel.org/
Link: https://lkml.kernel.org/r/20210817035027.174869074@goodmis.org

Suggested-by: Masami Hiramatsu <mhiramat@kernel.org>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

1 files changed, 12 insertions, 7 deletions

diff --git a/kernel/trace/trace_events_synth.c b/kernel/trace/trace_events_synth.c
index f4f5489e1e28..d54094b7a9d7 100644
--- a/kernel/trace/trace_events_synth.c
+++ b/kernel/trace/trace_events_synth.c
@@ -1369,13 +1369,15 @@ static int destroy_synth_event(struct synth_event *se)
 	int ret;
 
 	if (se->ref)
-		ret = -EBUSY;
-	else {
-		ret = unregister_synth_event(se);
-		if (!ret) {
-			dyn_event_remove(&se->devent);
-			free_synth_event(se);
-		}
+		return -EBUSY;
+
+	if (trace_event_dyn_busy(&se->call))
+		return -EBUSY;
+
+	ret = unregister_synth_event(se);
+	if (!ret) {
+		dyn_event_remove(&se->devent);
+		free_synth_event(se);
 	}
 
 	return ret;
@@ -2102,6 +2104,9 @@ static int synth_event_release(struct dyn_event *ev)
 	if (event->ref)
 		return -EBUSY;
 
+	if (trace_event_dyn_busy(&event->call))
+		return -EBUSY;
+
 	ret = unregister_synth_event(event);
 	if (ret)
 		return ret;