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Subject[PATCH] mm: slab: Avoid the use of one-element array and use struct_size() helper
Date
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[];
};

/*
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
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