tracing: Do not take trace_event_sem in print_event_fields()

JIRA: https://issues.redhat.com/browse/RHEL-115358

commit 0a8f11f
Author: Steven Rostedt <rostedt@goodmis.org>
Date:   Thu May 1 22:41:28 2025 -0400

    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: stable@vger.kernel.org
    Cc: Masami Hiramatsu <mhiramat@kernel.org>
    Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
    Link: https://lore.kernel.org/20250501224128.0b1f0571@batman.local.home
    Fixes: 80a7699 ("tracing: Add "fields" option to show raw trace event fields")
    Reported-by: syzbot+441582c1592938fccf09@syzkaller.appspotmail.com
    Closes: https://lore.kernel.org/all/6813ff5e.050a0220.14dd7d.001b.GAE@google.com/
    Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

Signed-off-by: Jerome Marchand <jmarchan@redhat.com>

Author: jeromemarchand

kernel/trace/trace_output.c

@@ -961,11 +961,12 @@ 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;
@@ -975,7 +976,6 @@ 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;