linux-kernel - Re: [PATCH] drm/tiny: Use kmalloc

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Message-ID: <cb0f0a36-0593-4d4c-8450-d086b9c99d87@suse.de>
Date: Sun, 19 Oct 2025 16:47:14 +0200
From: Thomas Zimmermann <tzimmermann@...e.de>
To: Greg KH <gregkh@...uxfoundation.org>,
 Mehdi Ben Hadj Khelifa <mehdi.benhadjkhelifa@...il.com>
Cc: lanzano.alex@...il.com, maarten.lankhorst@...ux.intel.com,
 mripard@...nel.org, airlied@...il.com, simona@...ll.ch,
 dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
 skhan@...uxfoundation.org, david.hunter.linux@...il.com, khalid@...nel.org,
 linux-kernel-mentees@...ts.linuxfoundation.org
Subject: Re: [PATCH] drm/tiny: Use kmalloc_array() instead of kmalloc()

Hi

Am 19.10.25 um 16:34 schrieb Greg KH:
> On Sun, Oct 19, 2025 at 04:12:28PM +0100, Mehdi Ben Hadj Khelifa wrote:
>> Replace kmalloc() with kmalloc_array() to correctly
>> handle array allocations and benefit from built-in overflow checking[1].
>>
>> [1]:https://docs.kernel.org/process/deprecated.html
>>
>> Signed-off-by: Mehdi Ben Hadj Khelifa <mehdi.benhadjkhelifa@...il.com>
>> ---
>>   drivers/gpu/drm/tiny/repaper.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/tiny/repaper.c b/drivers/gpu/drm/tiny/repaper.c
>> index 4824f863fdba..290132c24ff9 100644
>> --- a/drivers/gpu/drm/tiny/repaper.c
>> +++ b/drivers/gpu/drm/tiny/repaper.c
>> @@ -534,7 +534,7 @@ static int repaper_fb_dirty(struct drm_framebuffer *fb, const struct iosys_map *
>>   	DRM_DEBUG("Flushing [FB:%d] st=%ums\n", fb->base.id,
>>   		  epd->factored_stage_time);
>>   
>> -	buf = kmalloc(fb->width * fb->height / 8, GFP_KERNEL);
>> +	buf = kmalloc_array(fb->height / 8, fb->width, GFP_KERNEL);
> This isn't an array, so this function change doesn't seem to make much
> sense, right?  The size should have already been checked earlier in the
> call change to be correct.

Yes, we've recently received plenty of these pointless changes. The 
correct code would compute the number of bytes per pixel using 
drm_format_info_min_pitch() and multiply with fb->height. The latter 
could (maybe) use kmalloc_array(). It would still not be an array in the 
common sense.

Best regards
Thomas

>
> thanks,
>
> greg k-h

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)