linux-kernel - Re: [PATCH 1/2] rv: Fix wrong type cast in monitors

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Message-ID: <786688d8a5ab0d5228d271861416d49cc3a8ebc3.camel@redhat.com>
Date: Mon, 28 Jul 2025 10:59:01 +0200
From: Gabriele Monaco <gmonaco@...hat.com>
To: Nam Cao <namcao@...utronix.de>, Steven Rostedt <rostedt@...dmis.org>, 
 Masami Hiramatsu <mhiramat@...nel.org>, Mathieu Desnoyers
 <mathieu.desnoyers@...icios.com>, 	linux-trace-kernel@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] rv: Fix wrong type cast in monitors_show()

On Sun, 2025-07-27 at 19:31 +0200, Nam Cao wrote:
> Argument 'p' of monitors_show() is not a pointer to struct
> rv_monitor, it is actually a pointer to the list_head inside struct
> rv_monitor. Therefore it is wrong to cast 'p' to struct rv_monitor *.
> 
> This wrong type cast has been there since the beginning. But it still
> worked because the list_head was the first field in struct
> rv_monitor_def. This is no longer true since commit 24cbfe18d55a
> ("rv: Merge struct rv_monitor_def into struct rv_monitor") moved the
> list_head, and this wrong type cast became a functional problem.
> 
> Properly use container_of() instead.
> 
> Fixes: 24cbfe18d55a ("rv: Merge struct rv_monitor_def into struct
> rv_monitor")
> Signed-off-by: Nam Cao <namcao@...utronix.de>
> ---
>  kernel/trace/rv/rv.c | 2 +-
> 
> @@ -458,7 +458,7 @@ static int create_monitor_dir(struct rv_monitor
> *mon, struct rv_monitor *parent)
>   */
>  static int monitors_show(struct seq_file *m, void *p)
>  {
> -	struct rv_monitor *mon = p;
> +	struct rv_monitor *mon = container_of(p, struct rv_monitor,
> list);
>  

Good catch, thanks! The container_of is the way to go.
Do you have valid reasons not to move the list_head to the top? It's
not a big deal but it would save computing and summing the offset. It
doesn't seem name (the current first element) really needs to stay
there.

Thanks,
Gabriele

>  	if (mon->parent)
>  		seq_printf(m, "%s:%s\n", mon->parent->name, mon-
> >name);