[PATCH v1] USBNET: fix handling padding packet

[PATCH v1] USBNET: fix handling padding packet

[Ming Lei]

Commit 638c5115a7949(USBNET: support DMA SG) introduces DMA SG
if the usb host controller is capable of building packet from
discontinuous buffers, but missed handling padding packet when
building DMA SG.

This patch attachs the pre-allocated padding packet at the
end of the sg list, so padding packet can be sent to device
if drivers require that.

Reported-by: David Laight <David.Laight@aculab.com>
Acked-by: Oliver Neukum <oliver@neukum.org>
Signed-off-by: Ming Lei <ming.lei@canonical.com>
---
v1:
	- fix bug in case of dev->can_dma_sg and !urb->num_sgs
---
 drivers/net/usb/usbnet.c   |   27 +++++++++++++++++++++------
 include/linux/usb/usbnet.h |    1 +
 2 files changed, 22 insertions(+), 6 deletions(-)

diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c
index 7b331e6..bf94e10 100644
--- a/drivers/net/usb/usbnet.c
+++ b/drivers/net/usb/usbnet.c
@@ -1241,7 +1241,9 @@ static int build_dma_sg(const struct sk_buff *skb, struct urb *urb)
 	if (num_sgs == 1)
 		return 0;
 
-	urb->sg = kmalloc(num_sgs * sizeof(struct scatterlist), GFP_ATOMIC);
+	/* reserve one for zero packet */
+	urb->sg = kmalloc((num_sgs + 1) * sizeof(struct scatterlist),
+			  GFP_ATOMIC);
 	if (!urb->sg)
 		return -ENOMEM;
 
@@ -1305,7 +1307,7 @@ netdev_tx_t usbnet_start_xmit (struct sk_buff *skb,
 		if (build_dma_sg(skb, urb) < 0)
 			goto drop;
 	}
-	entry->length = length = urb->transfer_buffer_length;
+	length = urb->transfer_buffer_length;
 
 	/* don't assume the hardware handles USB_ZERO_PACKET
 	 * NOTE:  strictly conforming cdc-ether devices should expect
@@ -1317,15 +1319,18 @@ netdev_tx_t usbnet_start_xmit (struct sk_buff *skb,
 	if (length % dev->maxpacket == 0) {
 		if (!(info->flags & FLAG_SEND_ZLP)) {
 			if (!(info->flags & FLAG_MULTI_PACKET)) {
-				urb->transfer_buffer_length++;
-				if (skb_tailroom(skb)) {
+				length++;
+				if (skb_tailroom(skb) && !urb->num_sgs) {
 					skb->data[skb->len] = 0;
 					__skb_put(skb, 1);
-				}
+				} else if (urb->num_sgs)
+					sg_set_buf(&urb->sg[urb->num_sgs++],
+							dev->padding_pkt, 1);
 			}
 		} else
 			urb->transfer_flags |= URB_ZERO_PACKET;
 	}
+	entry->length = urb->transfer_buffer_length = length;
 
 	spin_lock_irqsave(&dev->txq.lock, flags);
 	retval = usb_autopm_get_interface_async(dev->intf);
@@ -1509,6 +1514,7 @@ void usbnet_disconnect (struct usb_interface *intf)
 
 	usb_kill_urb(dev->interrupt);
 	usb_free_urb(dev->interrupt);
+	kfree(dev->padding_pkt);
 
 	free_netdev(net);
 }
@@ -1679,9 +1685,16 @@ usbnet_probe (struct usb_interface *udev, const struct usb_device_id *prod)
 	/* initialize max rx_qlen and tx_qlen */
 	usbnet_update_max_qlen(dev);
 
+	if (dev->can_dma_sg && !(info->flags & FLAG_SEND_ZLP) &&
+		!(info->flags & FLAG_MULTI_PACKET)) {
+		dev->padding_pkt = kzalloc(1, GFP_KERNEL);
+		if (!dev->padding_pkt)
+			goto out4;
+	}
+
 	status = register_netdev (net);
 	if (status)
-		goto out4;
+		goto out5;
 	netif_info(dev, probe, dev->net,
 		   "register '%s' at usb-%s-%s, %s, %pM\n",
 		   udev->dev.driver->name,
@@ -1699,6 +1712,8 @@ usbnet_probe (struct usb_interface *udev, const struct usb_device_id *prod)
 
 	return 0;
 
+out5:
+	kfree(dev->padding_pkt);
 out4:
 	usb_free_urb(dev->interrupt);
 out3:
diff --git a/include/linux/usb/usbnet.h b/include/linux/usb/usbnet.h
index 9cb2fe8..e303eef 100644
--- a/include/linux/usb/usbnet.h
+++ b/include/linux/usb/usbnet.h
@@ -42,6 +42,7 @@ struct usbnet {
 	struct usb_host_endpoint *status;
 	unsigned		maxpacket;
 	struct timer_list	delay;
+	const char		*padding_pkt;
 
 	/* protocol/interface state */
 	struct net_device	*net;
-- 
1.7.9.5

Re: [PATCH v1] USBNET: fix handling padding packet

[Ming Lei]

On Mon, Sep 23, 2013 at 8:59 PM, Ming Lei <ming.lei-Z7WLFzj8eWMS+FvcfC7Uqw@public.gmane.org> wrote:
> Commit 638c5115a7949(USBNET: support DMA SG) introduces DMA SG
> if the usb host controller is capable of building packet from
> discontinuous buffers, but missed handling padding packet when
> building DMA SG.
>
> This patch attachs the pre-allocated padding packet at the
> end of the sg list, so padding packet can be sent to device
> if drivers require that.
>
> Reported-by: David Laight <David.Laight-JxhZ9S5GRejQT0dZR+AlfA@public.gmane.org>
> Acked-by: Oliver Neukum <oliver-GvhC2dPhHPQdnm+yROfE0A@public.gmane.org>
> Signed-off-by: Ming Lei <ming.lei-Z7WLFzj8eWMS+FvcfC7Uqw@public.gmane.org>
> ---
> v1:
>         - fix bug in case of dev->can_dma_sg and !urb->num_sgs

David, could you queue this patch in your tree? And it should fix
regression caused by commit 638c5115a7949(USBNET: support
DMA SG), since I found that without the padding the device can't
send out packets successfully if their length is dividable by max
packet size, and the problem can be observed with icmp sending:

 $ping -s 974 another_machine  #from host with ax99179_178a attached


Thanks,
--
Ming Lei
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Re: [PATCH v1] USBNET: fix handling padding packet

[David Miller]

From: Ming Lei <ming.lei-Z7WLFzj8eWMS+FvcfC7Uqw@public.gmane.org>
Date: Mon, 23 Sep 2013 20:59:35 +0800

> Commit 638c5115a7949(USBNET: support DMA SG) introduces DMA SG
> if the usb host controller is capable of building packet from
> discontinuous buffers, but missed handling padding packet when
> building DMA SG.
> 
> This patch attachs the pre-allocated padding packet at the
> end of the sg list, so padding packet can be sent to device
> if drivers require that.
> 
> Reported-by: David Laight <David.Laight-JxhZ9S5GRejQT0dZR+AlfA@public.gmane.org>
> Acked-by: Oliver Neukum <oliver-GvhC2dPhHPQdnm+yROfE0A@public.gmane.org>
> Signed-off-by: Ming Lei <ming.lei-Z7WLFzj8eWMS+FvcfC7Uqw@public.gmane.org>

Applied, thanks.

I still think the suggestion to disable scatter gather for
devices with the padding issue was the most sane approach
to solve this.

I guess people like supporting complicated crap and excess
code for things that pretty much do not exist, or at best
are not prominent enough to cater for at all.

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