From: Eric Dumazet <edumazet@google.com>
Date: Sat, 26 Oct 2013 00:26:17 +0000 (-0700)
Subject: tcp: gso: fix truesize tracking
X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=0d08c42cf9a71530fef5ebcfe368f38f2dd0476f;p=GitHub%2Fexynos8895%2Fandroid_kernel_samsung_universal8895.git

tcp: gso: fix truesize tracking

commit 6ff50cd55545 ("tcp: gso: do not generate out of order packets")
had an heuristic that can trigger a warning in skb_try_coalesce(),
because skb->truesize of the gso segments were exactly set to mss.

This breaks the requirement that

skb->truesize >= skb->len + truesizeof(struct sk_buff);

It can trivially be reproduced by :

ifconfig lo mtu 1500
ethtool -K lo tso off
netperf

As the skbs are looped into the TCP networking stack, skb_try_coalesce()
warns us of these skb under-estimating their truesize.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
---

diff --git a/net/ipv4/tcp_offload.c b/net/ipv4/tcp_offload.c
index 3a7525e6c086..533c58a5cfb7 100644
--- a/net/ipv4/tcp_offload.c
+++ b/net/ipv4/tcp_offload.c
@@ -18,6 +18,7 @@ struct sk_buff *tcp_tso_segment(struct sk_buff *skb,
 				netdev_features_t features)
 {
 	struct sk_buff *segs = ERR_PTR(-EINVAL);
+	unsigned int sum_truesize = 0;
 	struct tcphdr *th;
 	unsigned int thlen;
 	unsigned int seq;
@@ -102,13 +103,7 @@ struct sk_buff *tcp_tso_segment(struct sk_buff *skb,
 		if (copy_destructor) {
 			skb->destructor = gso_skb->destructor;
 			skb->sk = gso_skb->sk;
-			/* {tcp|sock}_wfree() use exact truesize accounting :
-			 * sum(skb->truesize) MUST be exactly be gso_skb->truesize
-			 * So we account mss bytes of 'true size' for each segment.
-			 * The last segment will contain the remaining.
-			 */
-			skb->truesize = mss;
-			gso_skb->truesize -= mss;
+			sum_truesize += skb->truesize;
 		}
 		skb = skb->next;
 		th = tcp_hdr(skb);
@@ -125,7 +120,9 @@ struct sk_buff *tcp_tso_segment(struct sk_buff *skb,
 	if (copy_destructor) {
 		swap(gso_skb->sk, skb->sk);
 		swap(gso_skb->destructor, skb->destructor);
-		swap(gso_skb->truesize, skb->truesize);
+		sum_truesize += skb->truesize;
+		atomic_add(sum_truesize - gso_skb->truesize,
+			   &skb->sk->sk_wmem_alloc);
 	}
 
 	delta = htonl(oldlen + (skb_tail_pointer(skb) -