[PATCH] percpu: Use struct_size() helper

[PATCH] percpu: Use struct_size() helper

[Gustavo A. R. Silva]

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@embeddedor.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

Re: [PATCH] percpu: Use struct_size() helper

[Dennis Zhou]

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@embeddedor.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