From: David Rientjes <rientjes@google.com>
To: Qianli Zhao <zhaoqianligood@gmail.com>, Roman Gushchin <guro@fb.com>
Cc: cl@linux.com, penberg@kernel.org, iamjoonsoo.kim@lge.com,
Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
clang-built-linux@googlegroups.com, zhaoqianli@xiaomi.com
Subject: Re: [PATCH] mm: slab: Avoid the use of one-element array and use struct_size() helper
Date: Wed, 29 Jul 2020 16:40:42 -0700 (PDT) [thread overview]
Message-ID: <alpine.DEB.2.23.453.2007291640140.3120473@chino.kir.corp.google.com> (raw)
In-Reply-To: <1596034214-15010-1-git-send-email-zhaoqianligood@gmail.com>
[-- Attachment #1: Type: text/plain, Size: 2201 bytes --]
On Wed, 29 Jul 2020, Qianli Zhao wrote:
> From: Qianli Zhao <zhaoqianli@xiaomi.com>
>
> There is a regular need in the kernel to provide a way to declare having a
> dynamically sized set of trailing elements in a structure. Kernel code should
> always use “flexible array members”[1] for these cases. The older style of
> one-element or zero-length arrays should no longer be used[2].
>
> Make use of the struct_size() helper instead of an open-coded version
> in order to avoid any potential type mistakes.
>
> [1] https://en.wikipedia.org/wiki/Flexible_array_member
> [2] https://github.com/KSPP/linux/issues/21
>
> Signed-off-by: Qianli Zhao <zhaoqianli@xiaomi.com>
> ---
> mm/slab.h | 2 +-
> mm/slab_common.c | 7 ++-----
> 2 files changed, 3 insertions(+), 6 deletions(-)
>
> diff --git a/mm/slab.h b/mm/slab.h
> index 74f7e09..c12fb65 100644
> --- a/mm/slab.h
> +++ b/mm/slab.h
> @@ -34,7 +34,7 @@ struct kmem_cache {
>
> struct memcg_cache_array {
> struct rcu_head rcu;
> - struct kmem_cache *entries[0];
> + struct kmem_cache *entries[];
> };
>
> /*
This is removed in the -mm tree, see
https://www.ozlabs.org/~akpm/mmotm/broken-out/mm-memcg-slab-use-a-single-set-of-kmem_caches-for-all-allocations.patch
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index fe8b684..56f4818 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -166,9 +166,7 @@ static int init_memcg_params(struct kmem_cache *s,
> if (!memcg_nr_cache_ids)
> return 0;
>
> - arr = kvzalloc(sizeof(struct memcg_cache_array) +
> - memcg_nr_cache_ids * sizeof(void *),
> - GFP_KERNEL);
> + arr = kvzalloc(struct_size(arr, entries, memcg_nr_cache_ids), GFP_KERNEL);
> if (!arr)
> return -ENOMEM;
>
> @@ -199,8 +197,7 @@ static int update_memcg_params(struct kmem_cache *s, int new_array_size)
> {
> struct memcg_cache_array *old, *new;
>
> - new = kvzalloc(sizeof(struct memcg_cache_array) +
> - new_array_size * sizeof(void *), GFP_KERNEL);
> + new = kvzalloc(struct_size(new, entries, new_array_size), GFP_KERNEL);
> if (!new)
> return -ENOMEM;
>
> --
> 2.7.4
>
>
next prev parent reply other threads:[~2020-07-29 23:40 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-29 14:50 [PATCH] mm: slab: Avoid the use of one-element array and use struct_size() helper Qianli Zhao
2020-07-29 23:40 ` David Rientjes [this message]
2020-07-30 0:12 ` Gustavo A. R. Silva
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