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

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.

Link: http://lkml.kernel.org/r/20190221154622.GA19599@embeddedor
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/swapfile.c b/mm/swapfile.c
index a14257ac0476c6b1eb3df753c89e14a2bf781e87..2b8d9c3fbb47fd7a5c2a711dad73c5889dfe0bb2 100644 (file)
--- 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);