Re: [PATH v3] tracing: Fix race condition in kprobe initialization causing NULL pointer dereference

[John Ogness]

On 2025-09-30, chenyuan_fl@xxxxxxx wrote:
> diff --git a/kernel/trace/trace_probe.h b/kernel/trace/trace_probe.h
> index 842383fbc03b..98b838591edc 100644
> --- a/kernel/trace/trace_probe.h
> +++ b/kernel/trace/trace_probe.h
> @@ -274,19 +274,19 @@ struct event_file_link {
>  static inline bool trace_probe_test_flag(struct trace_probe *tp,
>  					 unsigned int flag)
>  {
> -	return !!(tp->event->flags & flag);
> +	return !!(smp_load_acquire(&tp->event->flags) & flag);
>  }
>  
>  static inline void trace_probe_set_flag(struct trace_probe *tp,
>  					unsigned int flag)
>  {
> -	tp->event->flags |= flag;
> +	smp_store_release(&tp->event->flags, tp->event->flags | flag);
>  }
>  
>  static inline void trace_probe_clear_flag(struct trace_probe *tp,
>  					  unsigned int flag)
>  {
> -	tp->event->flags &= ~flag;
> +	smp_store_release(&tp->event->flags, tp->event->flags & ~flag);
>  }
>  
>  static inline bool trace_probe_is_enabled(struct trace_probe *tp)

I don't have any feedback about the correctness with regards to tracing
and kprobes. However, I recommend writing a comment at each necessary
memory barrier site. The comment should mention the pairing memory
barrier and the ordering it is guaranteeing.

John