linux-kernel - [PATCH 3.12 103/103] net-gro: reset skb->truesize in napi_reuse

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Message-Id: <ac993cf25a957b332864e3200644b50e179826fc.1401371259.git.jslaby@suse.cz>
Date:	Thu, 29 May 2014 15:49:28 +0200
From:	Jiri Slaby <jslaby@...e.cz>
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
	"David S. Miller" <davem@...emloft.net>,
	Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 103/103] net-gro: reset skb->truesize in napi_reuse_skb()

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

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

[ Upstream commit e33d0ba8047b049c9262fdb1fcafb93cb52ceceb ]

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>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 net/core/dev.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/core/dev.c b/net/core/dev.c
index 5a50e98aee2c..01d53d62a2ec 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3959,6 +3959,7 @@ 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;
 }
-- 
1.9.3

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