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

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Message-ID: <e4f0290b-5d15-472f-acee-e1e1b0629ec0@gmail.com>
Date: Mon, 20 Oct 2025 22:38:55 +0100
From: Mehdi Ben Hadj Khelifa <mehdi.benhadjkhelifa@...il.com>
To: Shuah Khan <skhan@...uxfoundation.org>, javierm@...hat.com,
 maarten.lankhorst@...ux.intel.com, mripard@...nel.org, tzimmermann@...e.de,
 airlied@...il.com, simona@...ll.ch
Cc: dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
 david.hunter.linux@...il.com, khalid@...nel.org,
 linux-kernel-mentees@...ts.linuxfoundation.org
Subject: Re: [PATCH] drm/solomon: Use kmalloc_array() instead of kmalloc()

On 10/20/25 9:08 PM, Shuah Khan wrote:
> On 10/19/25 08:58, Mehdi Ben Hadj Khelifa wrote:
>> Replace kmalloc() with kmalloc_array() in several places to correctly
>> handle array allocations and benefit from built-in overflow checking.
>> This prevents potential integer overflows[1] when computing allocation
>> sizes from width, height, pitch, or page values.
>>
>> [1]: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.
> 
the document[1] specifically quotes the following:"
Dynamic size calculations (especially multiplication) should not be 
performed in memory allocator (or similar) function arguments due to the 
risk of them overflowing. This could lead to values wrapping around and 
a smaller allocation being made than the caller was expecting. Using 
those allocations could lead to linear overflows of heap memory and 
other misbehaviors. (One exception to this is literal values where the 
compiler can warn if they might overflow. However, the preferred way in 
these cases is to refactor the code as suggested below to avoid the 
open-coded arithmetic.)"
Specifically mentionned the refactor of the code base in such cases 
which is why i'm doing the patches in the first place.Also i'm trying 
the best to send patches related to the issue where such issues of 
overflow are present or to be consistent with the same API used within 
the same subsystem.
[1]:https://docs.kernel.org/process/deprecated.html> How are you testing 
these changes - do you have this hardware?
> 
>>
I have a raspberrypi zero 2 wh that i'm using in combination with the 
ssd1306 OLED panel via I2C to test it's rendering and it's working 
properly by using modetest and seeing no regressions or warnings in dmesg.

Best Regards,
Mehdi Ben Hadj Khelifa

>> Signed-off-by: Mehdi Ben Hadj Khelifa <mehdi.benhadjkhelifa@...il.com>
>> ---
>>   drivers/gpu/drm/solomon/ssd130x.c | 6 +++---
>>   1 file changed, 3 insertions(+), 3 deletions(-)
>>
> 
> thanks,
> -- Shuah