Re: [PATCH v2] drm/log: Fix division by zero when scale module parameter is 0

[Jani Nikula]

On Wed, 29 Jul 2026, Jocelyn Falempe <jfalempe@xxxxxxxxxx> wrote:
> On 29/07/2026 12:58, oushixiong1025@xxxxxxx wrote:
>> From: Shixiong Ou <oushixiong@xxxxxxxxxx>
>> 
>> The scale module parameter can be set to 0 via kernel command line or
>> sysfs. When scale is 0, scaled_font_h and scaled_font_w become 0,
>> causing a division by zero in the rows/columns calculation.
>> 
>> Introduce a drm_log_scale() helper that returns scale ?: 1, and use it
>> at all read sites. This avoids a race that a setter-based clamp would
>> have between param_set_uint() and the subsequent check, where another
>> CPU could observe scale == 0.
>
> The scale module parameter is read only (that's the meaning of 0444 in 
> module_param()) so it can't be set by sysfs, or change at runtime.
>
> So this check can be done only once in drm_log_register().

Oops, missed this in my review completely, thanks!


-- 
Jani Nikula, Intel