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Subject: Re: [PATCH] mm: memcontrol: use struct_size() in kmalloc()
From:   William Kucharski <william.kucharski@oracle.com>
In-Reply-To: <20190104183726.GA6374@embeddedor>
Date:   Thu, 10 Jan 2019 05:12:17 -0700
Cc:     Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        cgroups@vger.kernel.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
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Message-Id: <8B12C965-1406-4464-96FF-B9C04187DD7D@oracle.com>
References: <20190104183726.GA6374@embeddedor>
To:     "Gustavo A. R. Silva" <gustavo@embeddedor.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


> On Jan 4, 2019, at 11:37 AM, Gustavo A. R. Silva =
<gustavo@embeddedor.com> wrote:
>=20
> 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:
>=20
> struct foo {
>    int stuff;
>    void *entry[];
> };
>=20
> instance =3D kmalloc(sizeof(struct foo) + sizeof(void *) * count, =
GFP_KERNEL);
>=20
> Instead of leaving these open-coded and prone to type mistakes, we can
> now use the new struct_size() helper:
>=20
> instance =3D kmalloc(struct_size(instance, entry, count), GFP_KERNEL);
>=20
> This code was detected with the help of Coccinelle.
>=20
> Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
> ---
> mm/memcontrol.c | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>=20
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index af7f18b32389..ad256cf7da47 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -3626,8 +3626,7 @@ static int =
__mem_cgroup_usage_register_event(struct mem_cgroup *memcg,
> 	size =3D thresholds->primary ? thresholds->primary->size + 1 : =
1;
>=20
> 	/* Allocate memory for new array of thresholds */
> -	new =3D kmalloc(sizeof(*new) + size * sizeof(struct =
mem_cgroup_threshold),
> -			GFP_KERNEL);
> +	new =3D kmalloc(struct_size(new, entries, size), GFP_KERNEL);
> 	if (!new) {
> 		ret =3D -ENOMEM;
> 		goto unlock;
> --=20
> 2.20.1
>=20

Reviewed-by: William Kucharski <william.kucharski@oracle.com>=