linux-kernel - Re: [PATCH] drm/xe/hwmon: Use devm_mutex

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Message-ID: <99686467b8d528b0bc9967989ef75df2fc6d1797.camel@intel.com>
Date: Mon, 8 Sep 2025 18:47:33 +0000
From: "Summers, Stuart" <stuart.summers@...el.com>
To: "simona@...ll.ch" <simona@...ll.ch>, "Vivi, Rodrigo"
	<rodrigo.vivi@...el.com>, "christophe.jaillet@...adoo.fr"
	<christophe.jaillet@...adoo.fr>, "De Marchi, Lucas"
	<lucas.demarchi@...el.com>, "thomas.hellstrom@...ux.intel.com"
	<thomas.hellstrom@...ux.intel.com>, "airlied@...il.com" <airlied@...il.com>
CC: "intel-xe@...ts.freedesktop.org" <intel-xe@...ts.freedesktop.org>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	"kernel-janitors@...r.kernel.org" <kernel-janitors@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/xe/hwmon: Use devm_mutex_init()

On Sun, 2025-09-07 at 15:42 +0200, Christophe JAILLET wrote:
> Use devm_mutex_init() instead of hand-writing it.
> 
> This saves some LoC, improves readability and saves some space in the
> generated .o file.
> 
> Before:
> ======
>    text    data     bss     dec     hex filename
>   36884   10296      64   47244    b88c drivers/gpu/drm/xe/xe_hwmon.o
> 
> After:
> =====
>    text    data     bss     dec     hex filename
>   36651   10224      64   46939    b75b drivers/gpu/drm/xe/xe_hwmon.o
> 
> Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
> ---
>  drivers/gpu/drm/xe/xe_hwmon.c | 10 +---------
>  1 file changed, 1 insertion(+), 9 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_hwmon.c
> b/drivers/gpu/drm/xe/xe_hwmon.c
> index 32a76ae6e9dc..e65382d4426a 100644
> --- a/drivers/gpu/drm/xe/xe_hwmon.c
> +++ b/drivers/gpu/drm/xe/xe_hwmon.c
> @@ -1294,13 +1294,6 @@ xe_hwmon_get_preregistration_info(struct
> xe_hwmon *hwmon)
>                         xe_hwmon_fan_input_read(hwmon, channel,
> &fan_speed);
>  }
>  
> -static void xe_hwmon_mutex_destroy(void *arg)
> -{
> -       struct xe_hwmon *hwmon = arg;
> -
> -       mutex_destroy(&hwmon->hwmon_lock);
> -}
> -
>  int xe_hwmon_register(struct xe_device *xe)
>  {
>         struct device *dev = xe->drm.dev;
> @@ -1319,8 +1312,7 @@ int xe_hwmon_register(struct xe_device *xe)
>         if (!hwmon)
>                 return -ENOMEM;
>  
> -       mutex_init(&hwmon->hwmon_lock);
> -       ret = devm_add_action_or_reset(dev, xe_hwmon_mutex_destroy,
> hwmon);
> +       ret = devm_mutex_init(dev, &hwmon->hwmon_lock);

Thanks for the patch! Yes I agree this looks better. And we don't want
to use drmm_mutex_init() here because, as was detailed in an earlier
fix here, we can't mix devm_kzalloc with drmm_mutex_init or risk a uaf.

Reviewed-by: Stuart Summers <stuart.summers@...el.com>

>         if (ret)
>                 return ret;
>