2019-08-29 19:07:12

by Gustavo A. R. Silva

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

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 <[email protected]>
---
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

2019-09-05 21:24:05

by Dennis Zhou

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 <[email protected]>
> ---
> 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