linux-kernel - Re: [PATCH] module: Fix implicit type conversion

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Date:   Mon, 8 Nov 2021 19:31:05 +0100 (CET)
From:   Miroslav Benes <mbenes@...e.cz>
To:     Jiasheng Jiang <jiasheng@...as.ac.cn>
cc:     jeyu@...nel.org, ast@...nel.org, daniel@...earbox.net,
        andrii@...nel.org, kafai@...com, songliubraving@...com, yhs@...com,
        john.fastabend@...il.com, kpsingh@...nel.org, nathan@...nel.org,
        ndesaulniers@...gle.com, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, bpf@...r.kernel.org,
        clang-built-linux@...glegroups.com, mcgrof@...nel.org
Subject: Re: [PATCH] module: Fix implicit type conversion

[CCing Luis]

Hi,

On Fri, 29 Oct 2021, Jiasheng Jiang wrote:

> The variable 'cpu' is defined as unsigned int.
> However in the for_each_possible_cpu, its values is assigned to -1.
> That doesn't make sense and in the cpumask_next() it is implicitly
> type conversed to int.
> It is universally accepted that the implicit type conversion is
> terrible.
> Also, having the good programming custom will set an example for
> others.
> Thus, it might be better to change the definition of 'cpu' from
> unsigned int to int.

Frankly, I don't see a benefit of changing this. It seems fine to me. 
Moreover this is not, by far, the only place in the kernel with the same 
pattern.

Miroslav

> Fixes: 10fad5e ("percpu, module: implement and use is_kernel/module_percpu_address()")
> Signed-off-by: Jiasheng Jiang <jiasheng@...as.ac.cn>
> ---
>  kernel/module.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/module.c b/kernel/module.c
> index 927d46c..f10d611 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -632,7 +632,7 @@ static void percpu_modcopy(struct module *mod,
>  bool __is_module_percpu_address(unsigned long addr, unsigned long *can_addr)
>  {
>  	struct module *mod;
> -	unsigned int cpu;
> +	int cpu;
>  
>  	preempt_disable();
>  
> -- 
> 2.7.4
>