linux-kernel - Re: [PATCH] tracing: Use refcount for trace_event

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Message-Id: <20240729234924.6accc2e6216e3b7be1a97e61@kernel.org>
Date: Mon, 29 Jul 2024 23:49:24 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: LKML <linux-kernel@...r.kernel.org>, Linux trace kernel
 <linux-trace-kernel@...r.kernel.org>, Masami Hiramatsu
 <mhiramat@...nel.org>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: Re: [PATCH] tracing: Use refcount for trace_event_file reference
 counter

On Fri, 26 Jul 2024 14:42:08 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> From: Steven Rostedt <rostedt@...dmis.org>
> 
> Instead of using an atomic counter for the trace_event_file reference
> counter, use the refcount interface. It has various checks to make sure
> the reference counting is correct, and will warn if it detects an error
> (like refcount_inc() on '0').
> 
> Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>

Looks good to me.

Masami Hiramatsu (Google) <mhiramat@...nel.org>

Thanks,

> ---
>  include/linux/trace_events.h | 2 +-
>  kernel/trace/trace_events.c  | 8 ++++----
>  2 files changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
> index 9df3e2973626..fed58e54f15e 100644
> --- a/include/linux/trace_events.h
> +++ b/include/linux/trace_events.h
> @@ -680,7 +680,7 @@ struct trace_event_file {
>  	 * caching and such. Which is mostly OK ;-)
>  	 */
>  	unsigned long		flags;
> -	atomic_t		ref;	/* ref count for opened files */
> +	refcount_t		ref;	/* ref count for opened files */
>  	atomic_t		sm_ref;	/* soft-mode reference counter */
>  	atomic_t		tm_ref;	/* trigger-mode reference counter */
>  };
> diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
> index 852643d957de..81ade9ddcbe5 100644
> --- a/kernel/trace/trace_events.c
> +++ b/kernel/trace/trace_events.c
> @@ -992,18 +992,18 @@ static void remove_subsystem(struct trace_subsystem_dir *dir)
>  
>  void event_file_get(struct trace_event_file *file)
>  {
> -	atomic_inc(&file->ref);
> +	refcount_inc(&file->ref);
>  }
>  
>  void event_file_put(struct trace_event_file *file)
>  {
> -	if (WARN_ON_ONCE(!atomic_read(&file->ref))) {
> +	if (WARN_ON_ONCE(!refcount_read(&file->ref))) {
>  		if (file->flags & EVENT_FILE_FL_FREED)
>  			kmem_cache_free(file_cachep, file);
>  		return;
>  	}
>  
> -	if (atomic_dec_and_test(&file->ref)) {
> +	if (refcount_dec_and_test(&file->ref)) {
>  		/* Count should only go to zero when it is freed */
>  		if (WARN_ON_ONCE(!(file->flags & EVENT_FILE_FL_FREED)))
>  			return;
> @@ -2999,7 +2999,7 @@ trace_create_new_event(struct trace_event_call *call,
>  	atomic_set(&file->tm_ref, 0);
>  	INIT_LIST_HEAD(&file->triggers);
>  	list_add(&file->list, &tr->events);
> -	event_file_get(file);
> +	refcount_set(&file->ref, 1);
>  
>  	return file;
>  }
> -- 
> 2.43.0
> 


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>