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: 80a76994b2d88 ("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>

diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
index fee40ffbd490614ba33cb9e2310ae274ac0142b6..b9ab06c9954323a427217835aece13f6bb420f34 100644 (file)
--- a/kernel/trace/trace_output.c
+++ b/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;