tracing: Do not take trace_event_sem in print_event_fields()

On some paths in print_event_fields() it takes the trace_event_sem for
read, even though it should always be held when the function is called.

Remove the taking of that mutex and add a lockdep_assert_held_read() to
make sure the trace_event_sem is held when print_event_fields() is called.

Cc: [email protected]
Cc: Masami Hiramatsu <[email protected]>
Cc: Mathieu Desnoyers <[email protected]>
Link: https://lore.kernel.org/[email protected]
Fixes: 80a7699 ("tracing: Add "fields" option to show raw trace event fields")
Reported-by: [email protected]
Closes: https://lore.kernel.org/all/[email protected]/
Signed-off-by: Steven Rostedt (Google) <[email protected]>

Author: rostedt

kernel/trace/trace_output.c

@@ -1042,11 +1042,12 @@ enum print_line_t print_event_fields(struct trace_iterator *iter,
 	struct trace_event_call *call;
 	struct list_head *head;
 
+	lockdep_assert_held_read(&trace_event_sem);
+
 	/* ftrace defined events have separate call structures */
 	if (event->type <= __TRACE_LAST_TYPE) {
 		bool found = false;
 
-		down_read(&trace_event_sem);
 		list_for_each_entry(call, &ftrace_events, list) {
 			if (call->event.type == event->type) {
 				found = true;
@@ -1056,7 +1057,6 @@ enum print_line_t print_event_fields(struct trace_iterator *iter,
 			if (call->event.type > __TRACE_LAST_TYPE)
 				break;
 		}
-		up_read(&trace_event_sem);
 		if (!found) {
 			trace_seq_printf(&iter->seq, "UNKNOWN TYPE %d\n", event->type);
 			goto out;