linux-kernel - Re: [PATCH] drm/drm_vblank.c: avoid unsigned int to signed int cast

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Message-ID: <5d7f9d1a-10c5-5b55-c7d8-24183f5a09ee@189.cn>
Date:   Tue, 23 May 2023 16:12:14 +0800
From:   Sui Jingfeng <15330273260@....cn>
To:     Sui Jingfeng <15330273260@....cn>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        David Laight <David.Laight@...LAB.COM>,
        Li Yi <liyi@...ngson.cn>
Cc:     Thomas Zimmermann <tzimmermann@...e.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "loongson-kernel@...ts.loongnix.cn" 
        <loongson-kernel@...ts.loongnix.cn>
Subject: Re: [PATCH] drm/drm_vblank.c: avoid unsigned int to signed int cast

Hi,

On 2023/5/23 12:26, Sui Jingfeng wrote:
> Hi,
>
> On 2023/5/22 19:29, Jani Nikula wrote:
>> In general, do not use unsigned types in arithmethic to avoid negative
>> values, because most people will be tripped over by integer promotion
>> rules, and you'll get negative values anyway.
>
>
> Here I'm sure about this,
>
Here, I'm NOT sure about this


> but there are plenty unsigned types arithmetic in the kernel.
>
> take kmalloc_array() function as an example in 
> /tools/virto/linux/kernel.h
>
>
> static inline void *kmalloc_array(unsigned n, size_t s, gfp_t gfp)
> {
>     return kmalloc(n * s, gfp);
> }
>
>
> NOTE that *size_t* is an unsigned integral data type.