rhashtable: 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);

This code was detected with the help of Coccinelle.

---
 lib/rhashtable.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

index a8583af43b59..9c84f5cef69c 100644
@@ -175,8 +175,7 @@ static struct bucket_table *bucket_table_alloc(struct rhashtable *ht,
 	int i;
 	static struct lock_class_key __key;
 
-	size = sizeof(*tbl) + nbuckets * sizeof(tbl->buckets[0]);
-	tbl = kvzalloc(size, gfp);
+	tbl = kvzalloc(struct_size(tbl, buckets, nbuckets), gfp);
 
 	size = nbuckets;
 

2.21.0

From: "Gustavo A. R. Silva" <[email protected]>
Date: Thu, 11 Apr 2019 18:43:06 -0500

Applied.