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

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Message-ID: <843484l2uj.fsf@jogness.linutronix.de>
Date: Tue, 30 Sep 2025 11:19:56 +0206
From: John Ogness <john.ogness@...utronix.de>
To: chenyuan_fl@....com, rostedt@...dmis.org, peterz@...radead.org
Cc: bigeasy@...utronix.de, chenyuan@...inos.cn,
 linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
 mathieu.desnoyers@...icios.com, mhiramat@...nel.org
Subject: Re: [PATH v3] tracing: Fix race condition in kprobe initialization
 causing NULL pointer dereference

On 2025-09-30, chenyuan_fl@....com 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