net: Fix truesize accounting in skb_gro_receive()

GRO is very optimistic in skb truesize estimates, only taking into
account the used part of fragments.

Be conservative, and use more precise computation, so that bloated GRO
skbs can be collapsed eventually.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Alexander Duyck <alexander.h.duyck@intel.com>
Cc: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Acked-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/skbuff.c

@@ -2871,6 +2871,7 @@ int skb_gro_receive(struct sk_buff **head, struct sk_buff *skb)
 	unsigned int len = skb_gro_len(skb);
 	unsigned int offset = skb_gro_offset(skb);
 	unsigned int headlen = skb_headlen(skb);
+	unsigned int delta_truesize;
 
 	if (p->len + len >= 65536)
 		return -E2BIG;
@@ -2900,11 +2901,14 @@ int skb_gro_receive(struct sk_buff **head, struct sk_buff *skb)
 		frag->page_offset += offset;
 		skb_frag_size_sub(frag, offset);
 
+		/* all fragments truesize : remove (head size + sk_buff) */
+		delta_truesize = skb->truesize - SKB_TRUESIZE(skb_end_pointer(skb) - skb->head);
+
 		skb->truesize -= skb->data_len;
 		skb->len -= skb->data_len;
 		skb->data_len = 0;
 
-		NAPI_GRO_CB(skb)->free = 1;
+		NAPI_GRO_CB(skb)->free = NAPI_GRO_FREE;
 		goto done;
 	} else if (skb->head_frag) {
 		int nr_frags = pinfo->nr_frags;
@@ -2929,6 +2933,7 @@ int skb_gro_receive(struct sk_buff **head, struct sk_buff *skb)
 		memcpy(frag + 1, skbinfo->frags, sizeof(*frag) * skbinfo->nr_frags);
 		/* We dont need to clear skbinfo->nr_frags here */
 
+		delta_truesize = skb->truesize - SKB_DATA_ALIGN(sizeof(struct sk_buff));
 		NAPI_GRO_CB(skb)->free = NAPI_GRO_FREE_STOLEN_HEAD;
 		goto done;
 	} else if (skb_gro_len(p) != pinfo->gso_size)
@@ -2971,7 +2976,7 @@ int skb_gro_receive(struct sk_buff **head, struct sk_buff *skb)
 	p = nskb;
 
 merge:
-	p->truesize += skb->truesize - len;
+	delta_truesize = skb->truesize;
 	if (offset > headlen) {
 		unsigned int eat = offset - headlen;
 
@@ -2991,7 +2996,7 @@ int skb_gro_receive(struct sk_buff **head, struct sk_buff *skb)
 done:
 	NAPI_GRO_CB(p)->count++;
 	p->data_len += len;
-	p->truesize += len;
+	p->truesize += delta_truesize;
 	p->len += len;
 
 	NAPI_GRO_CB(skb)->same_flow = 1;