[for-linus][PATCH 2/2] tracing: Add down_write(trace_event_sem) when adding trace event

[Steven Rostedt <rostedt@kernel.org>]

From: Steven Rostedt <rostedt@goodmis.org>

When a module is loaded, it adds trace events defined by the module. It
may also need to modify the modules trace printk formats to replace enum
names with their values.

If two modules are loaded at the same time, the adding of the event to the
ftrace_events list can corrupt the walking of the list in the code that is
modifying the printk format strings and crash the kernel.

The addition of the event should take the trace_event_sem for write while
it adds the new event.

Also add a lockdep_assert_held() on that semaphore in
__trace_add_event_dirs() as it iterates the list.

Cc: stable@vger.kernel.org
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Link: https://lore.kernel.org/20250718223158.799bfc0c@batman.local.home
Reported-by: Fusheng Huang(黄富生)  <Fusheng.Huang@luxshare-ict.com>
Closes: https://lore.kernel.org/all/20250717105007.46ccd18f@batman.local.home/
Fixes: 110bf2b764eb6 ("tracing: add protection around module events unload")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 kernel/trace/trace_events.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 120531268abf..d01e5c910ce1 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -3136,7 +3136,10 @@ __register_event(struct trace_event_call *call, struct module *mod)
 	if (ret < 0)
 		return ret;
 
+	down_write(&trace_event_sem);
 	list_add(&call->list, &ftrace_events);
+	up_write(&trace_event_sem);
+
 	if (call->flags & TRACE_EVENT_FL_DYNAMIC)
 		atomic_set(&call->refcnt, 0);
 	else
@@ -3750,6 +3753,8 @@ __trace_add_event_dirs(struct trace_array *tr)
 	struct trace_event_call *call;
 	int ret;
 
+	lockdep_assert_held(&trace_event_sem);
+
 	list_for_each_entry(call, &ftrace_events, list) {
 		ret = __trace_add_new_event(call, tr);
 		if (ret < 0)
-- 
2.47.2