netdev - [PATCH net] net-gro: reset skb->truesize in napi_reuse

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Date:	Thu, 03 Apr 2014 09:28:10 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev <netdev@...r.kernel.org>
Subject: [PATCH net] net-gro: reset skb->truesize in napi_reuse_skb()

From: Eric Dumazet <edumazet@...gle.com>

Recycling skb always had been very tough...

This time it appears GRO layer can accumulate skb->truesize
adjustments made by drivers when they attach a fragment to skb.

skb_gro_receive() can only subtract from skb->truesize the used part
of a fragment.

I spotted this problem seeing TcpExtPruneCalled and
TcpExtTCPRcvCollapsed that were unexpected with a recent kernel, where
TCP receive window should be sized properly to accept traffic coming
from a driver not overshooting skb->truesize.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 net/core/dev.c |    1 +
 1 file changed, 1 insertion(+)

diff --git a/net/core/dev.c b/net/core/dev.c
index 757063420ce0..8770984e1ddc 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4043,6 +4043,7 @@ static void napi_reuse_skb(struct napi_struct *napi, struct sk_buff *skb)
 	skb->vlan_tci = 0;
 	skb->dev = napi->dev;
 	skb->skb_iif = 0;
+	skb->truesize = SKB_TRUESIZE(skb_end_offset(skb));

 	napi->skb = skb;
 }

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