linux-kernel - Re: [PATCH] percpu: Use struct

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Message-ID: <20190905165452.GA41838@dennisz-mbp.dhcp.thefacebook.com>
Date:   Thu, 5 Sep 2019 12:54:52 -0400
From:   Dennis Zhou <dennis@...nel.org>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Cc:     Dennis Zhou <dennis@...nel.org>, Tejun Heo <tj@...nel.org>,
        Christoph Lameter <cl@...ux.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] percpu: Use struct_size() helper

On Thu, Aug 29, 2019 at 02:06:05PM -0500, Gustavo A. R. Silva wrote:
> One of the more common cases of allocation size calculations is finding
> the size of a structure that has a zero-sized array at the end, along
> with memory for some number of elements for that array. For example:
> 
> struct pcpu_alloc_info {
> 	...
>         struct pcpu_group_info  groups[];
> };
> 
> Make use of the struct_size() helper instead of an open-coded version
> in order to avoid any potential type mistakes.
> 
> So, replace the following form:
> 
> sizeof(*ai) + nr_groups * sizeof(ai->groups[0])
> 
> with:
> 
> struct_size(ai, groups, nr_groups)
> 
> This code was detected with the help of Coccinelle.
> 
> Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>
> ---
>  mm/percpu.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/percpu.c b/mm/percpu.c
> index 7e2aa0305c27..7e06a1e58720 100644
> --- a/mm/percpu.c
> +++ b/mm/percpu.c
> @@ -2125,7 +2125,7 @@ struct pcpu_alloc_info * __init pcpu_alloc_alloc_info(int nr_groups,
>  	void *ptr;
>  	int unit;
>  
> -	base_size = ALIGN(sizeof(*ai) + nr_groups * sizeof(ai->groups[0]),
> +	base_size = ALIGN(struct_size(ai, groups, nr_groups),
>  			  __alignof__(ai->groups[0].cpu_map[0]));
>  	ai_size = base_size + nr_units * sizeof(ai->groups[0].cpu_map[0]);
>  
> -- 
> 2.23.0
> 
> 

Hi Gustavo,

Sorry about the delay, I meant to get to this before the holiday. I've
applied it to for-5.4.

Thanks,
Dennis