[PATCH v3] drm/log: Fix division by zero when scale module parameter is 0

[PATCH v3] drm/log: Fix division by zero when scale module parameter is 0

[oushixiong1025]

From: Shixiong Ou <oushixiong@kylinos.cn>

The scale module parameter can be set to 0 via kernel command line.
When scale is 0, scaled_font_h and scaled_font_w become 0, causing
a division by zero in the rows/columns calculation.

Since the scale module parameter is read-only (0444 permissions), it
cannot be changed at runtime via sysfs. Clamp it to 1 once in
drm_log_register().

Signed-off-by: Shixiong Ou <oushixiong@kylinos.cn>
---
v2->v3:
   Clamp scale once in drm_log_register() instead of introducing a
   drm_log_scale() helper, since scale is read-only at runtime.

v1->v2:
   Introduce a drm_log_scale() helper.

diff --git a/drivers/gpu/drm/clients/drm_log.c b/drivers/gpu/drm/clients/drm_log.c
index 294b3be1a6b3..46004abd4e61 100644
--- a/drivers/gpu/drm/clients/drm_log.c
+++ b/drivers/gpu/drm/clients/drm_log.c
@@ -424,6 +424,9 @@ void drm_log_register(struct drm_device *dev)
 {
 	struct drm_log *new;
 
+	if (!scale)
+		scale = 1;
+
 	new = kzalloc_obj(*new);
 	if (!new)
 		goto err_warn;
--
2.25.1

No virus found
		Checked by Hillstone Network AntiVirus

Re: [PATCH v3] drm/log: Fix division by zero when scale module parameter is 0

[Jocelyn Falempe]

On 30/07/2026 03:44, oushixiong1025@163.com wrote:
> From: Shixiong Ou <oushixiong@kylinos.cn>
> 
> The scale module parameter can be set to 0 via kernel command line.
> When scale is 0, scaled_font_h and scaled_font_w become 0, causing
> a division by zero in the rows/columns calculation.
> 
> Since the scale module parameter is read-only (0444 permissions), it
> cannot be changed at runtime via sysfs. Clamp it to 1 once in
> drm_log_register().

Thanks, it looks good to me

Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>

> 
> Signed-off-by: Shixiong Ou <oushixiong@kylinos.cn>
> ---
> v2->v3:
>     Clamp scale once in drm_log_register() instead of introducing a
>     drm_log_scale() helper, since scale is read-only at runtime.
> 
> v1->v2:
>     Introduce a drm_log_scale() helper.
> 
> diff --git a/drivers/gpu/drm/clients/drm_log.c b/drivers/gpu/drm/clients/drm_log.c
> index 294b3be1a6b3..46004abd4e61 100644
> --- a/drivers/gpu/drm/clients/drm_log.c
> +++ b/drivers/gpu/drm/clients/drm_log.c
> @@ -424,6 +424,9 @@ void drm_log_register(struct drm_device *dev)
>   {
>   	struct drm_log *new;
>   
> +	if (!scale)
> +		scale = 1;
> +
>   	new = kzalloc_obj(*new);
>   	if (!new)
>   		goto err_warn;
> --
> 2.25.1
> 
> No virus found
> 		Checked by Hillstone Network AntiVirus
>