linux-kernel - [012/121] usbnet: do not pretend to support SG/TSO

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Message-ID: <lsq.1378608721.990890425@decadent.org.uk>
Date:	Sun, 08 Sep 2013 03:52:01 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "Eric Dumazet" <edumazet@...gle.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: [012/121] usbnet: do not pretend to support SG/TSO

3.2.51-rc1 review patch.  If anyone has any objections, please let me know.

------------------

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

[ Upstream commit 20f0170377264e8449b6987041f0bcc4d746d3ed ]

usbnet doesn't support yet SG, so drivers should not advertise SG or TSO
capabilities, as they allow TCP stack to build large TSO packets that
need to be linearized and might use order-5 pages.

This adds an extra copy overhead and possible allocation failures.

Current code ignore skb_linearize() return code so crashes are even
possible.

Best is to not pretend SG/TSO is supported, and add this again when/if
usbnet really supports SG for devices who could get a performance gain.

Based on a prior patch from Freddy Xin <freddy@...x.com.tw>

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/net/usb/smsc75xx.c | 12 +++---------
 1 file changed, 3 insertions(+), 9 deletions(-)

diff --git a/drivers/net/usb/smsc75xx.c b/drivers/net/usb/smsc75xx.c
index f3d17f8..a8e4640 100644
--- a/drivers/net/usb/smsc75xx.c
+++ b/drivers/net/usb/smsc75xx.c
@@ -43,7 +43,6 @@
 #define EEPROM_MAC_OFFSET		(0x01)
 #define DEFAULT_TX_CSUM_ENABLE		(true)
 #define DEFAULT_RX_CSUM_ENABLE		(true)
-#define DEFAULT_TSO_ENABLE		(true)
 #define SMSC75XX_INTERNAL_PHY_ID	(1)
 #define SMSC75XX_TX_OVERHEAD		(8)
 #define MAX_RX_FIFO_SIZE		(20 * 1024)
@@ -1035,17 +1034,14 @@ static int smsc75xx_bind(struct usbnet *dev, struct usb_interface *intf)
 
 	INIT_WORK(&pdata->set_multicast, smsc75xx_deferred_multicast_write);
 
-	if (DEFAULT_TX_CSUM_ENABLE) {
+	if (DEFAULT_TX_CSUM_ENABLE)
 		dev->net->features |= NETIF_F_IP_CSUM | NETIF_F_IPV6_CSUM;
-		if (DEFAULT_TSO_ENABLE)
-			dev->net->features |= NETIF_F_SG |
-				NETIF_F_TSO | NETIF_F_TSO6;
-	}
+
 	if (DEFAULT_RX_CSUM_ENABLE)
 		dev->net->features |= NETIF_F_RXCSUM;
 
 	dev->net->hw_features = NETIF_F_IP_CSUM | NETIF_F_IPV6_CSUM |
-		NETIF_F_SG | NETIF_F_TSO | NETIF_F_TSO6 | NETIF_F_RXCSUM;
+				NETIF_F_RXCSUM;
 
 	/* Init all registers */
 	ret = smsc75xx_reset(dev);
@@ -1170,8 +1166,6 @@ static struct sk_buff *smsc75xx_tx_fixup(struct usbnet *dev,
 {
 	u32 tx_cmd_a, tx_cmd_b;
 
-	skb_linearize(skb);
-
 	if (skb_headroom(skb) < SMSC75XX_TX_OVERHEAD) {
 		struct sk_buff *skb2 =
 			skb_copy_expand(skb, SMSC75XX_TX_OVERHEAD, 0, flags);

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