linux-kernel - Re: [PATCH] rv: Fix wrong type cast in enabled_monitors

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Message-ID: <8f379f2072ee12afda37455aa0ad4e37d53c4f2d.camel@redhat.com>
Date: Wed, 06 Aug 2025 14:45:22 +0200
From: Gabriele Monaco <gmonaco@...hat.com>
To: Nam Cao <namcao@...utronix.de>
Cc: 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] rv: Fix wrong type cast in enabled_monitors_next()



On Wed, 2025-08-06 at 14:09 +0200, Nam Cao wrote:
> Argument 'p' of enabled_monitors_next() 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.

Good catch, thanks!

Reviewed-by: Gabriele Monaco <gmonaco@...hat.com>

> 
> 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 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/rv/rv.c b/kernel/trace/rv/rv.c
> index bd7d56dbf6c2..6ce3495164d8 100644
> --- a/kernel/trace/rv/rv.c
> +++ b/kernel/trace/rv/rv.c
> @@ -495,7 +495,7 @@ static void *available_monitors_next(struct
> seq_file *m, void *p, loff_t *pos)
>   */
>  static void *enabled_monitors_next(struct seq_file *m, void *p,
> loff_t *pos)
>  {
> -	struct rv_monitor *mon = p;
> +	struct rv_monitor *mon = container_of(p, struct rv_monitor,
> list);
>  
>  	(*pos)++;
>