linux-kernel - Re: [PATCH] tracing: Show the tracer options in boot-time created instance

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Message-ID: <20251118133434.67def626@gandalf.local.home>
Date: Tue, 18 Nov 2025 13:34:34 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
Cc: Mark Rutland <mark.rutland@....com>, Mathieu Desnoyers
 <mathieu.desnoyers@...icios.com>, Andrew Morton
 <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH] tracing: Show the tracer options in boot-time created
 instance

On Tue, 18 Nov 2025 16:49:50 +0900
"Masami Hiramatsu (Google)" <mhiramat@...nel.org> wrote:

> From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
> 
> Since tracer_init_tracefs_work_func() only updates the tracer options
> for the global_trace, the instances created by the kernel cmdline
> do not have those options.
> 
> Fix to update tracer options for those boot-time created instances
> to show those options.
> 
> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
> Fixes: f20a580627f43 ("ftrace: Allow instances to use function tracing")

Actually, I think this should be:

Fixes: 428add559b69 ("tracing: Have tracer option be instance specific")

As it broke when we made function tracer options no longer global.

> ---
>  kernel/trace/trace.c |    4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 8ae95800592d..2e87060e1d5a 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -10903,6 +10903,7 @@ static struct notifier_block trace_module_nb = {
>  
>  static __init void tracer_init_tracefs_work_func(struct work_struct *work)
>  {
> +	struct trace_array *tr;
>  
>  	event_trace_init();
>  
> @@ -10937,7 +10938,8 @@ static __init void tracer_init_tracefs_work_func(struct work_struct *work)
>  
>  	create_trace_instances(NULL);
>  
> -	update_tracer_options(&global_trace);
> +	list_for_each_entry(tr, &ftrace_trace_arrays, list)
> +		update_tracer_options(tr);
>  }
>  
>  static __init int tracer_init_tracefs(void)

Since update_trace_options() is only called by this function, instead of
doing the loop here, change the function to be:

static __init void update_tracer_options(void)
{
	struct trace_array *tr;

	guard(mutex)(&trace_types_lock);
	tracer_options_updated = true;
	list_for_each_entry(tr, &ftrace_trace_arrays, list)
		__update_tracer_options(tr);
}

Thanks,

-- Steve