tracing: Only clear trace buffer on module unload if event was traced
Currently, when a module with events is unloaded, the trace buffer is
cleared. This is just a safety net in case the module might have some
strange callback when its event is outputted. But there's no reason
to reset the buffer if the module didn't have any of its events traced.
Add a flag to the event "call" structure called WAS_ENABLED and gets set
when the event is ever enabled, and this flag never gets cleared. When a
module gets unloaded, if any of its events have this flag set, then the
trace buffer will get cleared.
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 0f1307a..9a7dc4b 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -245,6 +245,9 @@
break;
}
file->flags |= FTRACE_EVENT_FL_ENABLED;
+
+ /* WAS_ENABLED gets set but never cleared. */
+ call->flags |= TRACE_EVENT_FL_WAS_ENABLED;
}
break;
}
@@ -1626,12 +1629,13 @@
{
struct ftrace_module_file_ops *file_ops;
struct ftrace_event_call *call, *p;
- bool found = false;
+ bool clear_trace = false;
down_write(&trace_event_mutex);
list_for_each_entry_safe(call, p, &ftrace_events, list) {
if (call->mod == mod) {
- found = true;
+ if (call->flags & TRACE_EVENT_FL_WAS_ENABLED)
+ clear_trace = true;
__trace_remove_event_call(call);
}
}
@@ -1648,9 +1652,9 @@
/*
* It is safest to reset the ring buffer if the module being unloaded
- * registered any events.
+ * registered any events that were used.
*/
- if (found)
+ if (clear_trace)
tracing_reset_current_online_cpus();
up_write(&trace_event_mutex);
}