Re: [PATCH] fprobe: Use guard(rcu_sched_notrace) and check rcu_is_watching()

[Masami Hiramatsu (Google)]

On Wed, 30 Sep 2026 16:03:25 -0400
Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:

> On Tue, 29 Sep 2026 09:19:12 +0900
> "Masami Hiramatsu (Google)" <mhiramat@xxxxxxxxxx> wrote:
> 
> > @@ -329,16 +333,14 @@ static void fprobe_ftrace_entry(unsigned long
> > ip, unsigned long parent_ip, struct fprobe *fp;
> >  	int bit;
> >  
> > +	if (!rcu_is_watching())
> > +		return;
> > +  
> 
> I'm thinking these should really be:
> 
> 	if (WARN_ON_ONCE(!rcu_is_watching()))
> 		return;

Hmm, is this for warning users to notice it is out of supported path?

If CONFIG_ARCH_WANTS_NO_INSTR=n, we will not prohibit user to set ftrace
avoiding the function where the RCU is not watching. So maybe it is hit
by user's operation.

Thank you,

> 
> -- Steve
> 



-- 
Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>