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

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Message-ID: <ea12faad-1735-4a49-a70d-d4cac5629042@linuxfoundation.org>
Date: Mon, 20 Oct 2025 14:06:12 -0600
From: Shuah Khan <skhan@...uxfoundation.org>
To: Jani Nikula <jani.nikula@...ux.intel.com>,
 Mehdi Ben Hadj Khelifa <mehdi.benhadjkhelifa@...il.com>,
 Thomas Zimmermann <tzimmermann@...e.de>, Greg KH <gregkh@...uxfoundation.org>
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,
 david.hunter.linux@...il.com, khalid@...nel.org,
 linux-kernel-mentees@...ts.linuxfoundation.org,
 Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH] drm/tiny: Use kmalloc_array() instead of kmalloc()

On 10/20/25 03:50, Jani Nikula wrote:
> On Sun, 19 Oct 2025, Mehdi Ben Hadj Khelifa <mehdi.benhadjkhelifa@...il.com> wrote:
>> On 10/19/25 3:47 PM, Thomas Zimmermann wrote:
>>> 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);
> 
> Also worth emphasizing that this is wildly wrong for any height that is
> not a multiple of 8.
> 
> And I thought I shot down a similar patch not long ago.
> 
> Is there some tool that suggests doing this? Fix the tool instead
> please.
> 

They are documented in https://docs.kernel.org/process/deprecated.html
Mu understanding is that this document lists deprecates APIs so people
don't keep adding new ones.

I didn't get the impression that we are supposed to go delete them from
the kernel and cause a churn.

thanks,
-- Shuah