[PATCH] mm/swapfile.c: use struct_size() in kvzalloc()

["Gustavo A. R. Silva" <gustavo@xxxxxxxxxxxxxx>]

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 foo {
    int stuff;
    struct boo entry[];
};

size = sizeof(struct foo) + count * sizeof(struct boo);
instance = kvzalloc(size, GFP_KERNEL);

Instead of leaving these open-coded and prone to type mistakes, we can
now use the new struct_size() helper:

instance = kvzalloc(struct_size(instance, entry, count), GFP_KERNEL);

Notice that, in this case, variable size is not necessary, hence
it is removed.

This code was detected with the help of Coccinelle.

Signed-off-by: Gustavo A. R. Silva <gustavo@xxxxxxxxxxxxxx>
---
 mm/swapfile.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index cca8420b12db..fd9b0025ad00 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -2713,9 +2713,8 @@ static struct swap_info_struct *alloc_swap_info(void)
 	struct swap_info_struct *p;
 	unsigned int type;
 	int i;
-	unsigned int size = sizeof(*p) + nr_node_ids * sizeof(struct plist_node);
 
-	p = kvzalloc(size, GFP_KERNEL);
+	p = kvzalloc(struct_size(p, avail_lists, nr_node_ids), GFP_KERNEL);
 	if (!p)
 		return ERR_PTR(-ENOMEM);
 
-- 
2.20.1