gro: simplify gro_list_prepare()

gro_list_prepare() always returns &napi->gro_hash[bucket].list,
without any variations. Moreover, it uses 'napi' argument only to
have access to this list, and calculates the bucket index for the
second time (firstly it happens at the beginning of
dev_gro_receive()) to do that.
Given that dev_gro_receive() already has an index to the needed
list, just pass it as the first argument to eliminate redundant
calculations, and make gro_list_prepare() return void.
Also, both arguments of gro_list_prepare() can be constified since
this function can only modify the skbs from the bucket list.
Signed-off-by: Alexander Lobakin <alobakin@pm.me>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/dev.c

@@ -5858,15 +5858,13 @@ void napi_gro_flush(struct napi_struct *napi, bool flush_old)
 }
 EXPORT_SYMBOL(napi_gro_flush);
 
-static struct list_head *gro_list_prepare(struct napi_struct *napi,
-					  struct sk_buff *skb)
+static void gro_list_prepare(const struct list_head *head,
+			     const struct sk_buff *skb)
 {
 	unsigned int maclen = skb->dev->hard_header_len;
 	u32 hash = skb_get_hash_raw(skb);
-	struct list_head *head;
 	struct sk_buff *p;
 
-	head = &napi->gro_hash[hash & (GRO_HASH_BUCKETS - 1)].list;
 	list_for_each_entry(p, head, list) {
 		unsigned long diffs;
 
@@ -5892,8 +5890,6 @@ static struct list_head *gro_list_prepare(struct napi_struct *napi,
 				       maclen);
 		NAPI_GRO_CB(p)->same_flow = !diffs;
 	}
-
-	return head;
 }
 
 static void skb_gro_reset_offset(struct sk_buff *skb)
@@ -5957,10 +5953,10 @@ static void gro_flush_oldest(struct napi_struct *napi, struct list_head *head)
 static enum gro_result dev_gro_receive(struct napi_struct *napi, struct sk_buff *skb)
 {
 	u32 hash = skb_get_hash_raw(skb) & (GRO_HASH_BUCKETS - 1);
+	struct list_head *gro_head = &napi->gro_hash[hash].list;
 	struct list_head *head = &offload_base;
 	struct packet_offload *ptype;
 	__be16 type = skb->protocol;
-	struct list_head *gro_head;
 	struct sk_buff *pp = NULL;
 	enum gro_result ret;
 	int same_flow;
@@ -5969,7 +5965,7 @@ static enum gro_result dev_gro_receive(struct napi_struct *napi, struct sk_buff
 	if (netif_elide_gro(skb->dev))
 		goto normal;
 
-	gro_head = gro_list_prepare(napi, skb);
+	gro_list_prepare(gro_head, skb);
 
 	rcu_read_lock();
 	list_for_each_entry_rcu(ptype, head, list) {