[PATCH 1/4] pch_gbe: Fix the checksum fill to the error location

[PATCH 1/4] pch_gbe: Fix the checksum fill to the error location

[Andy Cress]

Author: Zhong Hongbo <hongbo.zhong@windriver.com>

Due to some unknown hardware limitations the pch_gbe hardware cannot
calculate checksums when the length of network package is less
than 64 bytes, where we will surprisingly encounter a problem of
the destination IP incorrectly changed.

When forwarding network packages at the network layer the IP packages
won't be relayed to the upper transport layer and analyzed there,
consequently, skb->transport_header pointer will be mistakenly remained
the same as that of skb->network_header, resulting in TCP checksum
wrongly
filled into the field of destination IP in IP header.

We can fix this issue by manually calculate the offset of the TCP
checksum
 and update it accordingly.

We would normally use the skb_checksum_start_offset(skb) here, but in
this
case it is sometimes -2 (csum_start=0 - skb_headroom=2 => -2), hence the
manual calculation.

Signed-off-by: Zhong Hongbo <hongbo.zhong@windriver.com>
Merged-by: Andy Cress <andy.cress@us.kontron.com>

---
 drivers/net/pch_gbe/pch_gbe_main.c |   14 ++++++++------
 1 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/drivers/net/ethernet/oki-semi/pch_gbe/pch_gbe_main.c
b/drivers/net/ethernet/oki-semi/pch_gbe/pch_gbe_main.c
index 3787c64..1642bff 100644
--- a/drivers/net/ethernet/oki-semi/pch_gbe/pch_gbe_main.c
+++ b/drivers/net/ethernet/oki-semi/pch_gbe/pch_gbe_main.c
@@ -1178,32 +1178,35 @@ static void pch_gbe_tx_queue(struct
pch_gbe_adapter *adapter,
 	/*
 	 * It is because the hardware accelerator does not support a
checksum,
 	 * when the received data size is less than 64 bytes.
+	 * Note: skb_checksum_start_offset(skb) is sometimes -2 here.
 	 */
 	if (skb->len < PCH_GBE_SHORT_PKT && skb->ip_summed !=
CHECKSUM_NONE) {
+		struct iphdr *iph = ip_hdr(skb);
 		frame_ctrl |= PCH_GBE_TXD_CTRL_APAD |
 			      PCH_GBE_TXD_CTRL_TCPIP_ACC_OFF;
 		if (skb->protocol == htons(ETH_P_IP)) {
-			struct iphdr *iph = ip_hdr(skb);
 			unsigned int offset;
-			offset = skb_transport_offset(skb);
+			offset = (unsigned char *)((u8 *)iph + iph->ihl
* 4) - skb->data;
 			if (iph->protocol == IPPROTO_TCP) {
+				struct tcphdr *tcphdr_point = (struct
tcphdr *)((u8 *)iph + iph->ihl * 4);
 				skb->csum = 0;
-				tcp_hdr(skb)->check = 0;
+				tcphdr_point->check = 0;
 				skb->csum = skb_checksum(skb, offset,
 							 skb->len -
offset, 0);
-				tcp_hdr(skb)->check =
+				tcphdr_point->check = 
 					csum_tcpudp_magic(iph->saddr,
 							  iph->daddr,
 							  skb->len -
offset,
 							  IPPROTO_TCP,
 							  skb->csum);
 			} else if (iph->protocol == IPPROTO_UDP) {
+				struct udphdr *udphdr_point = (struct
udphdr *)((u8 *)iph + iph->ihl * 4);
 				skb->csum = 0;
-				udp_hdr(skb)->check = 0;
+				udphdr_point->check = 0;
 				skb->csum =
 					skb_checksum(skb, offset,
 						     skb->len - offset,
0);
-				udp_hdr(skb)->check =
+				udphdr_point->check = 
 					csum_tcpudp_magic(iph->saddr,
 							  iph->daddr,
 							  skb->len -
offset,

Re: [PATCH 1/4] pch_gbe: Fix the checksum fill to the error location

[Paul Gortmaker]

Hi Andy,

On Mon, Jul 16, 2012 at 4:03 PM, Andy Cress <andy.cress@us.kontron.com> wrote:
>
> Author: Zhong Hongbo <hongbo.zhong@windriver.com>

I'm curious as to how you are generating these mails, since if it
were with the "normal" method, then the above would have a
"From: " prefix, and not "Author: " prefix.  (More on what is the
"normal" method below...)

>
> Due to some unknown hardware limitations the pch_gbe hardware cannot
> calculate checksums when the length of network package is less
> than 64 bytes, where we will surprisingly encounter a problem of
> the destination IP incorrectly changed.

This has the feel of a problem that isn't properly understood, and
a solution that is aimed at masking the symptom at the point
where it rears its ugly head...  Not a good sign, when it comes to
requesting upstream acceptance.

>
> When forwarding network packages at the network layer the IP packages

s/packages/packets/

> won't be relayed to the upper transport layer and analyzed there,
> consequently, skb->transport_header pointer will be mistakenly remained
> the same as that of skb->network_header, resulting in TCP checksum
> wrongly
> filled into the field of destination IP in IP header.

Similarly here, the one-word-per-line symptom seems to hint at it
being a case of data manually entered into a GUI MUA, which
generally translates into headaches for the maintainer who has
to integrate your work.  If you can adopt a "standard" workflow,
it will be easier for both you and the maintainer.  And that
"standard" workflow could be something as simple as this:

--------------------------
cd /path/to/my/git-repo/of/net-next
git pull
git checkout -b pch-fixes master
<create commits, by cherry-pick or manual creation>
<validate with compilation, boot testing>
git format-patch --subject-prefix="PATCH net-next" --cover-letter -o
sendme master..pch-fixes
vi sendme/0000-cover-letter.patch
<enter text describing your series of patches>
git send-email --to netdev@vger.kernel.org -cc maintainer@someaddress.com sendme
-------------------------

>
> We can fix this issue by manually calculate the offset of the TCP
> checksum
>  and update it accordingly.
>
> We would normally use the skb_checksum_start_offset(skb) here, but in
> this
> case it is sometimes -2 (csum_start=0 - skb_headroom=2 => -2), hence the
> manual calculation.
>
> Signed-off-by: Zhong Hongbo <hongbo.zhong@windriver.com>
> Merged-by: Andy Cress <andy.cress@us.kontron.com>

There really isn't a precedent for Merged-by: -- you may want to see:

     http://kerneltrap.org/taxonomy/term/245

A "real" merge actually creates a merge commit, which is unique
in its own right.  So here, if you've carried forward an older patch,
or similar, you'd be most likely to add your own SOB line underneath.

Also a Cc: addition might be in order, say based on the output of:

./scripts/get_maintainer.pl -f drivers/net/ethernet/oki-semi/pch_gbe

A Cc: line put here goes on record.  If you use the --cc option
mentioned above, the Cc: record is limited to the mail header in
the netdev mail archive.

>
> ---
>  drivers/net/pch_gbe/pch_gbe_main.c |   14 ++++++++------
>  1 files changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/net/ethernet/oki-semi/pch_gbe/pch_gbe_main.c
> b/drivers/net/ethernet/oki-semi/pch_gbe/pch_gbe_main.c
> index 3787c64..1642bff 100644
> --- a/drivers/net/ethernet/oki-semi/pch_gbe/pch_gbe_main.c
> +++ b/drivers/net/ethernet/oki-semi/pch_gbe/pch_gbe_main.c
> @@ -1178,32 +1178,35 @@ static void pch_gbe_tx_queue(struct
> pch_gbe_adapter *adapter,
>         /*
>          * It is because the hardware accelerator does not support a
> checksum,
>          * when the received data size is less than 64 bytes.
> +        * Note: skb_checksum_start_offset(skb) is sometimes -2 here.

This comment is borderline useless, without some level of justification
of how/why that happens, and why it is OK/acceptable.

>          */
>         if (skb->len < PCH_GBE_SHORT_PKT && skb->ip_summed !=
> CHECKSUM_NONE) {
> +               struct iphdr *iph = ip_hdr(skb);
>                 frame_ctrl |= PCH_GBE_TXD_CTRL_APAD |
>                               PCH_GBE_TXD_CTRL_TCPIP_ACC_OFF;
>                 if (skb->protocol == htons(ETH_P_IP)) {
> -                       struct iphdr *iph = ip_hdr(skb);
>                         unsigned int offset;
> -                       offset = skb_transport_offset(skb);
> +                       offset = (unsigned char *)((u8 *)iph + iph->ihl
> * 4) - skb->data;
>                         if (iph->protocol == IPPROTO_TCP) {
> +                               struct tcphdr *tcphdr_point = (struct
> tcphdr *)((u8 *)iph + iph->ihl * 4);

There are several things going on here that are not ideal.  There
are casts of casts with unexplained math magic, there is the
attempt to encode variable types ("_point") in the variable name,
and there is apparently mailer munging which inserts rogue newlines.

At this point, I'd have to suggest that you go back to trying to
describe the use case, and the exact symptoms you are seeing
there; describe that and how you believe it comes about as
articulately as possible, and ask for input on how best to deal
with it; giving reference to this as a workaround that was deployed
some time in the past. In the end, this is a recipe for a good
commit log anyways, i.e. describing the end user symptom,
the use case that triggers it, the underlying reason as to why
it happens, and finally the technically correct fix to deal with
solving it (and indicate why it is the correct fix, if not obvious.)

Hope this helps with basic process and expectations.

Paul.
--

>                                 skb->csum = 0;
> -                               tcp_hdr(skb)->check = 0;
> +                               tcphdr_point->check = 0;
>                                 skb->csum = skb_checksum(skb, offset,
>                                                          skb->len -
> offset, 0);
> -                               tcp_hdr(skb)->check =
> +                               tcphdr_point->check =
>                                         csum_tcpudp_magic(iph->saddr,
>                                                           iph->daddr,
>                                                           skb->len -
> offset,
>                                                           IPPROTO_TCP,
>                                                           skb->csum);
>                         } else if (iph->protocol == IPPROTO_UDP) {
> +                               struct udphdr *udphdr_point = (struct
> udphdr *)((u8 *)iph + iph->ihl * 4);
>                                 skb->csum = 0;
> -                               udp_hdr(skb)->check = 0;
> +                               udphdr_point->check = 0;
>                                 skb->csum =
>                                         skb_checksum(skb, offset,
>                                                      skb->len - offset,
> 0);
> -                               udp_hdr(skb)->check =
> +                               udphdr_point->check =
>                                         csum_tcpudp_magic(iph->saddr,
>                                                           iph->daddr,
>                                                           skb->len -
> offset,
> --
> To unsubscribe from this list: send the line "unsubscribe netdev" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: [PATCH 1/4] pch_gbe: Fix the checksum fill to the error location

[Eric Dumazet]

On Mon, 2012-07-16 at 13:03 -0700, Andy Cress wrote:
> Author: Zhong Hongbo <hongbo.zhong@windriver.com>
> 
> Due to some unknown hardware limitations the pch_gbe hardware cannot
> calculate checksums when the length of network package is less
> than 64 bytes, where we will surprisingly encounter a problem of
> the destination IP incorrectly changed.
> 
> When forwarding network packages at the network layer the IP packages
> won't be relayed to the upper transport layer and analyzed there,
> consequently, skb->transport_header pointer will be mistakenly remained
> the same as that of skb->network_header, resulting in TCP checksum
> wrongly
> filled into the field of destination IP in IP header.
> 
> We can fix this issue by manually calculate the offset of the TCP
> checksum
>  and update it accordingly.
> 
> We would normally use the skb_checksum_start_offset(skb) here, but in
> this
> case it is sometimes -2 (csum_start=0 - skb_headroom=2 => -2), hence the
> manual calculation.
> 
> Signed-off-by: Zhong Hongbo <hongbo.zhong@windriver.com>
> Merged-by: Andy Cress <andy.cress@us.kontron.com>


Hmm... I fail to understand why you care about NIC doing checksums,
while pch_gbe_tx_queue() make a _copy_ of each outgoing
packets.

There _must_ be a way to avoid most of these copies (ie not touching
payload), only mess with the header to insert these 2 nul bytes ?

/* [Header:14][payload] ---> [Header:14][paddong:2][payload]    */

So at device setup : dev->needed_headroom = 2;

and in xmit,

	if (skb_headroom(skb) < 2) {
		struct sk_buff *skb_new;

		skb_new = skb_realloc_headroom(skb, 2);
		if (!skb_new) { handle error }
		consume_skb(skb);
		skb = skb_new;
	}
	ptr = skb_push(skb, 2);
	memmove(ptr, ptr + 2, ETH_HLEN);
	ptr[ETH_HLEN] = 0;
	ptr[ETH_HLEN + 1] = 0;

Re: [PATCH 1/4] pch_gbe: Fix the checksum fill to the error location

[Eric Dumazet]

On Tue, 2012-07-17 at 09:09 +0200, Eric Dumazet wrote:

> Hmm... I fail to understand why you care about NIC doing checksums,
> while pch_gbe_tx_queue() make a _copy_ of each outgoing
> packets.
> 
> There _must_ be a way to avoid most of these copies (ie not touching
> payload), only mess with the header to insert these 2 nul bytes ?
> 
> /* [Header:14][payload] ---> [Header:14][paddong:2][payload]    */
> 
> So at device setup : dev->needed_headroom = 2;
> 
> and in xmit,
> 
> 	if (skb_headroom(skb) < 2) {
> 		struct sk_buff *skb_new;
> 
> 		skb_new = skb_realloc_headroom(skb, 2);
> 		if (!skb_new) { handle error }
> 		consume_skb(skb);
> 		skb = skb_new;
> 	}
> 	ptr = skb_push(skb, 2);
> 	memmove(ptr, ptr + 2, ETH_HLEN);
> 	ptr[ETH_HLEN] = 0;
> 	ptr[ETH_HLEN + 1] = 0;
> 
> 

Something like the following (untested) patch


 drivers/net/ethernet/oki-semi/pch_gbe/pch_gbe_main.c |   55 +++++-----
 1 file changed, 29 insertions(+), 26 deletions(-)

diff --git a/drivers/net/ethernet/oki-semi/pch_gbe/pch_gbe_main.c b/drivers/net/ethernet/oki-semi/pch_gbe/pch_gbe_main.c
index b100656..2d3d982 100644
--- a/drivers/net/ethernet/oki-semi/pch_gbe/pch_gbe_main.c
+++ b/drivers/net/ethernet/oki-semi/pch_gbe/pch_gbe_main.c
@@ -1163,7 +1163,7 @@ static void pch_gbe_tx_queue(struct pch_gbe_adapter *adapter,
 	struct pch_gbe_hw *hw = &adapter->hw;
 	struct pch_gbe_tx_desc *tx_desc;
 	struct pch_gbe_buffer *buffer_info;
-	struct sk_buff *tmp_skb;
+	char *ptr;
 	unsigned int frame_ctrl;
 	unsigned int ring_num;
 
@@ -1221,18 +1221,27 @@ static void pch_gbe_tx_queue(struct pch_gbe_adapter *adapter,
 
 
 	buffer_info = &tx_ring->buffer_info[ring_num];
-	tmp_skb = buffer_info->skb;
+	if (skb_headroom(skb) < 2) {
+		struct sk_buff *skb_new;
+
+		skb_new = skb_realloc_headroom(skb, 2);
+		if (!skb_new) {
+			tx_ring->next_to_use = ring_num;
+			dev_kfree_skb_any(skb);
+			return;
+		}
+		consume_skb(skb);
+		skb = skb_new;
+	}
 
 	/* [Header:14][payload] ---> [Header:14][paddong:2][payload]    */
-	memcpy(tmp_skb->data, skb->data, ETH_HLEN);
-	tmp_skb->data[ETH_HLEN] = 0x00;
-	tmp_skb->data[ETH_HLEN + 1] = 0x00;
-	tmp_skb->len = skb->len;
-	memcpy(&tmp_skb->data[ETH_HLEN + 2], &skb->data[ETH_HLEN],
-	       (skb->len - ETH_HLEN));
+	ptr = skb_push(skb, 2);
+	memmove(ptr, ptr + 2, ETH_HLEN);
+	ptr[ETH_HLEN] = 0x00;
+	ptr[ETH_HLEN + 1] = 0x00;
 	/*-- Set Buffer information --*/
-	buffer_info->length = tmp_skb->len;
-	buffer_info->dma = dma_map_single(&adapter->pdev->dev, tmp_skb->data,
+	buffer_info->length = skb->len;
+	buffer_info->dma = dma_map_single(&adapter->pdev->dev, skb->data,
 					  buffer_info->length,
 					  DMA_TO_DEVICE);
 	if (dma_mapping_error(&adapter->pdev->dev, buffer_info->dma)) {
@@ -1240,18 +1249,20 @@ static void pch_gbe_tx_queue(struct pch_gbe_adapter *adapter,
 		buffer_info->dma = 0;
 		buffer_info->time_stamp = 0;
 		tx_ring->next_to_use = ring_num;
+		dev_kfree_skb_any(skb);
 		return;
 	}
 	buffer_info->mapped = true;
 	buffer_info->time_stamp = jiffies;
+	buffer_info->skb = skb;
 
 	/*-- Set Tx descriptor --*/
 	tx_desc = PCH_GBE_TX_DESC(*tx_ring, ring_num);
-	tx_desc->buffer_addr = (buffer_info->dma);
-	tx_desc->length = (tmp_skb->len);
-	tx_desc->tx_words_eob = ((tmp_skb->len + 3));
+	tx_desc->buffer_addr = buffer_info->dma;
+	tx_desc->length = skb->len;
+	tx_desc->tx_words_eob = skb->len + 3;
 	tx_desc->tx_frame_ctrl = (frame_ctrl);
-	tx_desc->gbec_status = (DSC_INIT16);
+	tx_desc->gbec_status = DSC_INIT16;
 
 	if (unlikely(++ring_num == tx_ring->count))
 		ring_num = 0;
@@ -1265,7 +1276,6 @@ static void pch_gbe_tx_queue(struct pch_gbe_adapter *adapter,
 	pch_tx_timestamp(adapter, skb);
 #endif
 
-	dev_kfree_skb_any(skb);
 }
 
 /**
@@ -1543,19 +1553,12 @@ static void pch_gbe_alloc_tx_buffers(struct pch_gbe_adapter *adapter,
 					struct pch_gbe_tx_ring *tx_ring)
 {
 	struct pch_gbe_buffer *buffer_info;
-	struct sk_buff *skb;
 	unsigned int i;
-	unsigned int bufsz;
 	struct pch_gbe_tx_desc *tx_desc;
 
-	bufsz =
-	    adapter->hw.mac.max_frame_size + PCH_GBE_DMA_ALIGN + NET_IP_ALIGN;
-
 	for (i = 0; i < tx_ring->count; i++) {
 		buffer_info = &tx_ring->buffer_info[i];
-		skb = netdev_alloc_skb(adapter->netdev, bufsz);
-		skb_reserve(skb, PCH_GBE_DMA_ALIGN);
-		buffer_info->skb = skb;
+		buffer_info->skb = NULL;
 		tx_desc = PCH_GBE_TX_DESC(*tx_ring, i);
 		tx_desc->gbec_status = (DSC_INIT16);
 	}
@@ -1622,9 +1625,9 @@ pch_gbe_clean_tx(struct pch_gbe_adapter *adapter,
 					 buffer_info->length, DMA_TO_DEVICE);
 			buffer_info->mapped = false;
 		}
-		if (buffer_info->skb) {
-			pr_debug("trim buffer_info->skb : %d\n", i);
-			skb_trim(buffer_info->skb, 0);
+		if (skb) {
+			dev_kfree_skb_any(skb);
+			buffer_info->skb = NULL;
 		}
 		tx_desc->gbec_status = DSC_INIT16;
 		if (unlikely(++i == tx_ring->count))

Re: [PATCH 1/4] pch_gbe: Fix the checksum fill to the error location

[Zhong Hongbo]

On 07/17/2012 03:09 PM, Eric Dumazet wrote:
> On Mon, 2012-07-16 at 13:03 -0700, Andy Cress wrote:
>> Author: Zhong Hongbo <hongbo.zhong@windriver.com>
>>
>> Due to some unknown hardware limitations the pch_gbe hardware cannot
>> calculate checksums when the length of network package is less
>> than 64 bytes, where we will surprisingly encounter a problem of
>> the destination IP incorrectly changed.
>>
>> When forwarding network packages at the network layer the IP packages
>> won't be relayed to the upper transport layer and analyzed there,
>> consequently, skb->transport_header pointer will be mistakenly remained
>> the same as that of skb->network_header, resulting in TCP checksum
>> wrongly
>> filled into the field of destination IP in IP header.
>>
>> We can fix this issue by manually calculate the offset of the TCP
>> checksum
>>  and update it accordingly.
>>
>> We would normally use the skb_checksum_start_offset(skb) here, but in
>> this
>> case it is sometimes -2 (csum_start=0 - skb_headroom=2 => -2), hence the
>> manual calculation.
>>
>> Signed-off-by: Zhong Hongbo <hongbo.zhong@windriver.com>
>> Merged-by: Andy Cress <andy.cress@us.kontron.com>
>
> Hmm... I fail to understand why you care about NIC doing checksums,

Hi Eric,

When forwarding network packages at the network layer, the variable value of skb->transport_header is unknown. In my test, the variable value of skb->transport_header is equal to skb->network_header. So When you count the checksum as following:

offset = skb_transport_offset(skb);

skb->csum = skb_checksum(skb, offset, skb->len - offset, 0);
We should only count the TCP checksum, But it maybe include IP part.

tcp_hdr(skb)->check = csum_tcpudp_magic(iph->saddr, iph->daddr, skb->len - offset, IPPROTO_TCP, skb->csum);
We should fill the checksum in TCP package, But maybe fill it in other location and cover the useful information, such as source ip.

So We should count the TCP checksum and fill it in the correct location. Or else the forwarding network package will be drop for the error checksum.


> while pch_gbe_tx_queue() make a _copy_ of each outgoing
> packets.
>
> There _must_ be a way to avoid most of these copies (ie not touching
> payload), only mess with the header to insert these 2 nul bytes ?

This is other fix, my patch just fix checksum error issue.

Thanks,
hongbo

>
> /* [Header:14][payload] ---> [Header:14][paddong:2][payload]    */
>
> So at device setup : dev->needed_headroom = 2;
>
> and in xmit,
>
> 	if (skb_headroom(skb) < 2) {
> 		struct sk_buff *skb_new;
>
> 		skb_new = skb_realloc_headroom(skb, 2);
> 		if (!skb_new) { handle error }
> 		consume_skb(skb);
> 		skb = skb_new;
> 	}
> 	ptr = skb_push(skb, 2);
> 	memmove(ptr, ptr + 2, ETH_HLEN);
> 	ptr[ETH_HLEN] = 0;
> 	ptr[ETH_HLEN + 1] = 0;
>
>
>
>
>

Re: [PATCH 1/4] pch_gbe: Fix the checksum fill to the error location

[Eric Dumazet]

On Tue, 2012-07-17 at 16:04 +0800, Zhong Hongbo wrote:

> Hi Eric,
> 
> When forwarding network packages at the network layer, the variable
> value of skb->transport_header is unknown. In my test, the variable
> value of skb->transport_header is equal to skb->network_header. So
> When you count the checksum as following:
> 
> offset = skb_transport_offset(skb);
> 
> skb->csum = skb_checksum(skb, offset, skb->len - offset, 0);
> We should only count the TCP checksum, But it maybe include IP part.
> 
> tcp_hdr(skb)->check = csum_tcpudp_magic(iph->saddr, iph->daddr,
> skb->len - offset, IPPROTO_TCP, skb->csum);
> We should fill the checksum in TCP package, But maybe fill it in other
> location and cover the useful information, such as source ip.
> 
> So We should count the TCP checksum and fill it in the correct
> location. Or else the forwarding network package will be drop for the
> error checksum.
> 



So maybe you should instead test 

if (skb->ip_summed == CHECKSUM_PARTIAL) {
	...
	skb_checksum_start_offset(skb); /* is valid */
}

RE: [PATCH 1/4] pch_gbe: Fix the checksum fill to the error location

[Andy Cress]

Eric,

This is intriguing, and the data copy also would explain why this transmit path is slow, and is susceptible to transmit timeouts.  
I want to apply and test your proposed patch, but I'll have to do that next week.

Andy

-----Original Message-----
From: Eric Dumazet [mailto:eric.dumazet@gmail.com] 
Sent: Tuesday, July 17, 2012 3:33 AM
To: Andy Cress
Cc: netdev@vger.kernel.org; Zhong Hongbo
Subject: Re: [PATCH 1/4] pch_gbe: Fix the checksum fill to the error location

On Tue, 2012-07-17 at 09:09 +0200, Eric Dumazet wrote:

> Hmm... I fail to understand why you care about NIC doing checksums,
> while pch_gbe_tx_queue() make a _copy_ of each outgoing
> packets.
> 
> There _must_ be a way to avoid most of these copies (ie not touching
> payload), only mess with the header to insert these 2 nul bytes ?
> 
> /* [Header:14][payload] ---> [Header:14][paddong:2][payload]    */
> 
> So at device setup : dev->needed_headroom = 2;
> 
> and in xmit,
> 
> 	if (skb_headroom(skb) < 2) {
> 		struct sk_buff *skb_new;
> 
> 		skb_new = skb_realloc_headroom(skb, 2);
> 		if (!skb_new) { handle error }
> 		consume_skb(skb);
> 		skb = skb_new;
> 	}
> 	ptr = skb_push(skb, 2);
> 	memmove(ptr, ptr + 2, ETH_HLEN);
> 	ptr[ETH_HLEN] = 0;
> 	ptr[ETH_HLEN + 1] = 0;
> 
> 

Something like the following (untested) patch


 drivers/net/ethernet/oki-semi/pch_gbe/pch_gbe_main.c |   55 +++++-----
 1 file changed, 29 insertions(+), 26 deletions(-)

diff --git a/drivers/net/ethernet/oki-semi/pch_gbe/pch_gbe_main.c b/drivers/net/ethernet/oki-semi/pch_gbe/pch_gbe_main.c
index b100656..2d3d982 100644
--- a/drivers/net/ethernet/oki-semi/pch_gbe/pch_gbe_main.c
+++ b/drivers/net/ethernet/oki-semi/pch_gbe/pch_gbe_main.c
@@ -1163,7 +1163,7 @@ static void pch_gbe_tx_queue(struct pch_gbe_adapter *adapter,
 	struct pch_gbe_hw *hw = &adapter->hw;
 	struct pch_gbe_tx_desc *tx_desc;
 	struct pch_gbe_buffer *buffer_info;
-	struct sk_buff *tmp_skb;
+	char *ptr;
 	unsigned int frame_ctrl;
 	unsigned int ring_num;
 
@@ -1221,18 +1221,27 @@ static void pch_gbe_tx_queue(struct pch_gbe_adapter *adapter,
 
 
 	buffer_info = &tx_ring->buffer_info[ring_num];
-	tmp_skb = buffer_info->skb;
+	if (skb_headroom(skb) < 2) {
+		struct sk_buff *skb_new;
+
+		skb_new = skb_realloc_headroom(skb, 2);
+		if (!skb_new) {
+			tx_ring->next_to_use = ring_num;
+			dev_kfree_skb_any(skb);
+			return;
+		}
+		consume_skb(skb);
+		skb = skb_new;
+	}
 
 	/* [Header:14][payload] ---> [Header:14][paddong:2][payload]    */
-	memcpy(tmp_skb->data, skb->data, ETH_HLEN);
-	tmp_skb->data[ETH_HLEN] = 0x00;
-	tmp_skb->data[ETH_HLEN + 1] = 0x00;
-	tmp_skb->len = skb->len;
-	memcpy(&tmp_skb->data[ETH_HLEN + 2], &skb->data[ETH_HLEN],
-	       (skb->len - ETH_HLEN));
+	ptr = skb_push(skb, 2);
+	memmove(ptr, ptr + 2, ETH_HLEN);
+	ptr[ETH_HLEN] = 0x00;
+	ptr[ETH_HLEN + 1] = 0x00;
 	/*-- Set Buffer information --*/
-	buffer_info->length = tmp_skb->len;
-	buffer_info->dma = dma_map_single(&adapter->pdev->dev, tmp_skb->data,
+	buffer_info->length = skb->len;
+	buffer_info->dma = dma_map_single(&adapter->pdev->dev, skb->data,
 					  buffer_info->length,
 					  DMA_TO_DEVICE);
 	if (dma_mapping_error(&adapter->pdev->dev, buffer_info->dma)) {
@@ -1240,18 +1249,20 @@ static void pch_gbe_tx_queue(struct pch_gbe_adapter *adapter,
 		buffer_info->dma = 0;
 		buffer_info->time_stamp = 0;
 		tx_ring->next_to_use = ring_num;
+		dev_kfree_skb_any(skb);
 		return;
 	}
 	buffer_info->mapped = true;
 	buffer_info->time_stamp = jiffies;
+	buffer_info->skb = skb;
 
 	/*-- Set Tx descriptor --*/
 	tx_desc = PCH_GBE_TX_DESC(*tx_ring, ring_num);
-	tx_desc->buffer_addr = (buffer_info->dma);
-	tx_desc->length = (tmp_skb->len);
-	tx_desc->tx_words_eob = ((tmp_skb->len + 3));
+	tx_desc->buffer_addr = buffer_info->dma;
+	tx_desc->length = skb->len;
+	tx_desc->tx_words_eob = skb->len + 3;
 	tx_desc->tx_frame_ctrl = (frame_ctrl);
-	tx_desc->gbec_status = (DSC_INIT16);
+	tx_desc->gbec_status = DSC_INIT16;
 
 	if (unlikely(++ring_num == tx_ring->count))
 		ring_num = 0;
@@ -1265,7 +1276,6 @@ static void pch_gbe_tx_queue(struct pch_gbe_adapter *adapter,
 	pch_tx_timestamp(adapter, skb);
 #endif
 
-	dev_kfree_skb_any(skb);
 }
 
 /**
@@ -1543,19 +1553,12 @@ static void pch_gbe_alloc_tx_buffers(struct pch_gbe_adapter *adapter,
 					struct pch_gbe_tx_ring *tx_ring)
 {
 	struct pch_gbe_buffer *buffer_info;
-	struct sk_buff *skb;
 	unsigned int i;
-	unsigned int bufsz;
 	struct pch_gbe_tx_desc *tx_desc;
 
-	bufsz =
-	    adapter->hw.mac.max_frame_size + PCH_GBE_DMA_ALIGN + NET_IP_ALIGN;
-
 	for (i = 0; i < tx_ring->count; i++) {
 		buffer_info = &tx_ring->buffer_info[i];
-		skb = netdev_alloc_skb(adapter->netdev, bufsz);
-		skb_reserve(skb, PCH_GBE_DMA_ALIGN);
-		buffer_info->skb = skb;
+		buffer_info->skb = NULL;
 		tx_desc = PCH_GBE_TX_DESC(*tx_ring, i);
 		tx_desc->gbec_status = (DSC_INIT16);
 	}
@@ -1622,9 +1625,9 @@ pch_gbe_clean_tx(struct pch_gbe_adapter *adapter,
 					 buffer_info->length, DMA_TO_DEVICE);
 			buffer_info->mapped = false;
 		}
-		if (buffer_info->skb) {
-			pr_debug("trim buffer_info->skb : %d\n", i);
-			skb_trim(buffer_info->skb, 0);
+		if (skb) {
+			dev_kfree_skb_any(skb);
+			buffer_info->skb = NULL;
 		}
 		tx_desc->gbec_status = DSC_INIT16;
 		if (unlikely(++i == tx_ring->count))

RE: [PATCH 1/4] pch_gbe: Fix the checksum fill to the error location

[Andy Cress]

Eric,

For the checksum patch, that needs to be tabled until Hongbo has a chance to evaluate/revise it, but that isn't vital to the goal of avoiding transmit timeouts, so the other 3 patches should still go forward.  I'll submit a revised patch set with just those 3.  

I tried applying the dont-copy-payload patch you outlined below, and for some reason it won't send successfully with that change.   I'm not sure why though.  This approach seems sound, and should greatly help transmit performance, if I could figure out what else it needs.  

Andy

-----Original Message-----
From: Eric Dumazet [mailto:eric.dumazet@gmail.com] 
Sent: Tuesday, July 17, 2012 3:33 AM
To: Andy Cress
Cc: netdev@vger.kernel.org; Zhong Hongbo
Subject: Re: [PATCH 1/4] pch_gbe: Fix the checksum fill to the error location

On Tue, 2012-07-17 at 09:09 +0200, Eric Dumazet wrote:

> Hmm... I fail to understand why you care about NIC doing checksums,
> while pch_gbe_tx_queue() make a _copy_ of each outgoing
> packets.
> 
> There _must_ be a way to avoid most of these copies (ie not touching
> payload), only mess with the header to insert these 2 nul bytes ?
> 
> /* [Header:14][payload] ---> [Header:14][paddong:2][payload]    */
> 
> So at device setup : dev->needed_headroom = 2;
> 
> and in xmit,
> 
> 	if (skb_headroom(skb) < 2) {
> 		struct sk_buff *skb_new;
> 
> 		skb_new = skb_realloc_headroom(skb, 2);
> 		if (!skb_new) { handle error }
> 		consume_skb(skb);
> 		skb = skb_new;
> 	}
> 	ptr = skb_push(skb, 2);
> 	memmove(ptr, ptr + 2, ETH_HLEN);
> 	ptr[ETH_HLEN] = 0;
> 	ptr[ETH_HLEN + 1] = 0;
> 
> 

Something like the following (untested) patch


 drivers/net/ethernet/oki-semi/pch_gbe/pch_gbe_main.c |   55 +++++-----
 1 file changed, 29 insertions(+), 26 deletions(-)

diff --git a/drivers/net/ethernet/oki-semi/pch_gbe/pch_gbe_main.c b/drivers/net/ethernet/oki-semi/pch_gbe/pch_gbe_main.c
index b100656..2d3d982 100644
--- a/drivers/net/ethernet/oki-semi/pch_gbe/pch_gbe_main.c
+++ b/drivers/net/ethernet/oki-semi/pch_gbe/pch_gbe_main.c
@@ -1163,7 +1163,7 @@ static void pch_gbe_tx_queue(struct pch_gbe_adapter *adapter,
 	struct pch_gbe_hw *hw = &adapter->hw;
 	struct pch_gbe_tx_desc *tx_desc;
 	struct pch_gbe_buffer *buffer_info;
-	struct sk_buff *tmp_skb;
+	char *ptr;
 	unsigned int frame_ctrl;
 	unsigned int ring_num;
 
@@ -1221,18 +1221,27 @@ static void pch_gbe_tx_queue(struct pch_gbe_adapter *adapter,
 
 
 	buffer_info = &tx_ring->buffer_info[ring_num];
-	tmp_skb = buffer_info->skb;
+	if (skb_headroom(skb) < 2) {
+		struct sk_buff *skb_new;
+
+		skb_new = skb_realloc_headroom(skb, 2);
+		if (!skb_new) {
+			tx_ring->next_to_use = ring_num;
+			dev_kfree_skb_any(skb);
+			return;
+		}
+		consume_skb(skb);
+		skb = skb_new;
+	}
 
 	/* [Header:14][payload] ---> [Header:14][paddong:2][payload]    */
-	memcpy(tmp_skb->data, skb->data, ETH_HLEN);
-	tmp_skb->data[ETH_HLEN] = 0x00;
-	tmp_skb->data[ETH_HLEN + 1] = 0x00;
-	tmp_skb->len = skb->len;
-	memcpy(&tmp_skb->data[ETH_HLEN + 2], &skb->data[ETH_HLEN],
-	       (skb->len - ETH_HLEN));
+	ptr = skb_push(skb, 2);
+	memmove(ptr, ptr + 2, ETH_HLEN);
+	ptr[ETH_HLEN] = 0x00;
+	ptr[ETH_HLEN + 1] = 0x00;
 	/*-- Set Buffer information --*/
-	buffer_info->length = tmp_skb->len;
-	buffer_info->dma = dma_map_single(&adapter->pdev->dev, tmp_skb->data,
+	buffer_info->length = skb->len;
+	buffer_info->dma = dma_map_single(&adapter->pdev->dev, skb->data,
 					  buffer_info->length,
 					  DMA_TO_DEVICE);
 	if (dma_mapping_error(&adapter->pdev->dev, buffer_info->dma)) {
@@ -1240,18 +1249,20 @@ static void pch_gbe_tx_queue(struct pch_gbe_adapter *adapter,
 		buffer_info->dma = 0;
 		buffer_info->time_stamp = 0;
 		tx_ring->next_to_use = ring_num;
+		dev_kfree_skb_any(skb);
 		return;
 	}
 	buffer_info->mapped = true;
 	buffer_info->time_stamp = jiffies;
+	buffer_info->skb = skb;
 
 	/*-- Set Tx descriptor --*/
 	tx_desc = PCH_GBE_TX_DESC(*tx_ring, ring_num);
-	tx_desc->buffer_addr = (buffer_info->dma);
-	tx_desc->length = (tmp_skb->len);
-	tx_desc->tx_words_eob = ((tmp_skb->len + 3));
+	tx_desc->buffer_addr = buffer_info->dma;
+	tx_desc->length = skb->len;
+	tx_desc->tx_words_eob = skb->len + 3;
 	tx_desc->tx_frame_ctrl = (frame_ctrl);
-	tx_desc->gbec_status = (DSC_INIT16);
+	tx_desc->gbec_status = DSC_INIT16;
 
 	if (unlikely(++ring_num == tx_ring->count))
 		ring_num = 0;
@@ -1265,7 +1276,6 @@ static void pch_gbe_tx_queue(struct pch_gbe_adapter *adapter,
 	pch_tx_timestamp(adapter, skb);
 #endif
 
-	dev_kfree_skb_any(skb);
 }
 
 /**
@@ -1543,19 +1553,12 @@ static void pch_gbe_alloc_tx_buffers(struct pch_gbe_adapter *adapter,
 					struct pch_gbe_tx_ring *tx_ring)
 {
 	struct pch_gbe_buffer *buffer_info;
-	struct sk_buff *skb;
 	unsigned int i;
-	unsigned int bufsz;
 	struct pch_gbe_tx_desc *tx_desc;
 
-	bufsz =
-	    adapter->hw.mac.max_frame_size + PCH_GBE_DMA_ALIGN + NET_IP_ALIGN;
-
 	for (i = 0; i < tx_ring->count; i++) {
 		buffer_info = &tx_ring->buffer_info[i];
-		skb = netdev_alloc_skb(adapter->netdev, bufsz);
-		skb_reserve(skb, PCH_GBE_DMA_ALIGN);
-		buffer_info->skb = skb;
+		buffer_info->skb = NULL;
 		tx_desc = PCH_GBE_TX_DESC(*tx_ring, i);
 		tx_desc->gbec_status = (DSC_INIT16);
 	}
@@ -1622,9 +1625,9 @@ pch_gbe_clean_tx(struct pch_gbe_adapter *adapter,
 					 buffer_info->length, DMA_TO_DEVICE);
 			buffer_info->mapped = false;
 		}
-		if (buffer_info->skb) {
-			pr_debug("trim buffer_info->skb : %d\n", i);
-			skb_trim(buffer_info->skb, 0);
+		if (skb) {
+			dev_kfree_skb_any(skb);
+			buffer_info->skb = NULL;
 		}
 		tx_desc->gbec_status = DSC_INIT16;
 		if (unlikely(++i == tx_ring->count))

RE: pch_gbe: dont-copy-payload (was [PATCH 1/4] ...)

[Andy Cress]

I found out why the proposed dont-copy-payload patch didn't work with this pch_gbe NIC.
This NIC PHY requires 64-byte-aligned DMA, and the transmit buffers won't be transferred if skb->data is not 64-byte-aligned.  Apparently the data copy has a by-product of aligning the buffers.  

I tried using skb_reserve(skb,64) in pch_gbe_alloc_tx_buffers and pch-gbe_alloc_rx_buffers, but that didn't seem to resolve it.

How can I make sure that the transmit data buffers are 64-byte-aligned?

Andy

-----Original Message-----
From: Andy Cress
Sent: Wednesday, July 25, 2012 4:11 PM
Subject: RE: [PATCH 1/4] pch_gbe: Fix the checksum fill to the error location

[...]
I tried applying the dont-copy-payload patch you outlined below, and for some reason it won't send successfully with that change.   I'm not sure why though.  This approach seems sound, and should greatly help transmit performance, if I could figure out what else it needs.  

Andy

-----Original Message-----
From: Eric Dumazet 
Sent: Tuesday, July 17, 2012 3:33 AM
To: Andy Cress
Cc: netdev@vger.kernel.org; Zhong Hongbo
Subject: Re: [PATCH 1/4] pch_gbe: Fix the checksum fill to the error location

On Tue, 2012-07-17 at 09:09 +0200, Eric Dumazet wrote:
[...]
> There _must_ be a way to avoid most of these copies (ie not touching
> payload), only mess with the header to insert these 2 nul bytes ?
> 
> /* [Header:14][payload] ---> [Header:14][paddong:2][payload]    */
[...]

Something like the following (untested) patch


 drivers/net/ethernet/oki-semi/pch_gbe/pch_gbe_main.c |   55 +++++-----
 1 file changed, 29 insertions(+), 26 deletions(-)

diff --git a/drivers/net/ethernet/oki-semi/pch_gbe/pch_gbe_main.c b/drivers/net/ethernet/oki-semi/pch_gbe/pch_gbe_main.c
index b100656..2d3d982 100644
--- a/drivers/net/ethernet/oki-semi/pch_gbe/pch_gbe_main.c
+++ b/drivers/net/ethernet/oki-semi/pch_gbe/pch_gbe_main.c
@@ -1163,7 +1163,7 @@ static void pch_gbe_tx_queue(struct pch_gbe_adapter *adapter,
 	struct pch_gbe_hw *hw = &adapter->hw;
 	struct pch_gbe_tx_desc *tx_desc;
 	struct pch_gbe_buffer *buffer_info;
-	struct sk_buff *tmp_skb;
+	char *ptr;
 	unsigned int frame_ctrl;
 	unsigned int ring_num;
 
@@ -1221,18 +1221,27 @@ static void pch_gbe_tx_queue(struct pch_gbe_adapter *adapter,
 
 
 	buffer_info = &tx_ring->buffer_info[ring_num];
-	tmp_skb = buffer_info->skb;
+	if (skb_headroom(skb) < 2) {
+		struct sk_buff *skb_new;
+
+		skb_new = skb_realloc_headroom(skb, 2);
+		if (!skb_new) {
+			tx_ring->next_to_use = ring_num;
+			dev_kfree_skb_any(skb);
+			return;
+		}
+		consume_skb(skb);
+		skb = skb_new;
+	}
 
 	/* [Header:14][payload] ---> [Header:14][paddong:2][payload]    */
-	memcpy(tmp_skb->data, skb->data, ETH_HLEN);
-	tmp_skb->data[ETH_HLEN] = 0x00;
-	tmp_skb->data[ETH_HLEN + 1] = 0x00;
-	tmp_skb->len = skb->len;
-	memcpy(&tmp_skb->data[ETH_HLEN + 2], &skb->data[ETH_HLEN],
-	       (skb->len - ETH_HLEN));
+	ptr = skb_push(skb, 2);
+	memmove(ptr, ptr + 2, ETH_HLEN);
+	ptr[ETH_HLEN] = 0x00;
+	ptr[ETH_HLEN + 1] = 0x00;
 	/*-- Set Buffer information --*/
-	buffer_info->length = tmp_skb->len;
-	buffer_info->dma = dma_map_single(&adapter->pdev->dev, tmp_skb->data,
+	buffer_info->length = skb->len;
+	buffer_info->dma = dma_map_single(&adapter->pdev->dev, skb->data,
 					  buffer_info->length,
 					  DMA_TO_DEVICE);
 	if (dma_mapping_error(&adapter->pdev->dev, buffer_info->dma)) {
@@ -1240,18 +1249,20 @@ static void pch_gbe_tx_queue(struct pch_gbe_adapter *adapter,
 		buffer_info->dma = 0;
 		buffer_info->time_stamp = 0;
 		tx_ring->next_to_use = ring_num;
+		dev_kfree_skb_any(skb);
 		return;
 	}
 	buffer_info->mapped = true;
 	buffer_info->time_stamp = jiffies;
+	buffer_info->skb = skb;
 
 	/*-- Set Tx descriptor --*/
 	tx_desc = PCH_GBE_TX_DESC(*tx_ring, ring_num);
-	tx_desc->buffer_addr = (buffer_info->dma);
-	tx_desc->length = (tmp_skb->len);
-	tx_desc->tx_words_eob = ((tmp_skb->len + 3));
+	tx_desc->buffer_addr = buffer_info->dma;
+	tx_desc->length = skb->len;
+	tx_desc->tx_words_eob = skb->len + 3;
 	tx_desc->tx_frame_ctrl = (frame_ctrl);
-	tx_desc->gbec_status = (DSC_INIT16);
+	tx_desc->gbec_status = DSC_INIT16;
 
 	if (unlikely(++ring_num == tx_ring->count))
 		ring_num = 0;
@@ -1265,7 +1276,6 @@ static void pch_gbe_tx_queue(struct pch_gbe_adapter *adapter,
 	pch_tx_timestamp(adapter, skb);
 #endif
 
-	dev_kfree_skb_any(skb);
 }
 
 /**
@@ -1543,19 +1553,12 @@ static void pch_gbe_alloc_tx_buffers(struct pch_gbe_adapter *adapter,
 					struct pch_gbe_tx_ring *tx_ring)
 {
 	struct pch_gbe_buffer *buffer_info;
-	struct sk_buff *skb;
 	unsigned int i;
-	unsigned int bufsz;
 	struct pch_gbe_tx_desc *tx_desc;
 
-	bufsz =
-	    adapter->hw.mac.max_frame_size + PCH_GBE_DMA_ALIGN + NET_IP_ALIGN;
-
 	for (i = 0; i < tx_ring->count; i++) {
 		buffer_info = &tx_ring->buffer_info[i];
-		skb = netdev_alloc_skb(adapter->netdev, bufsz);
-		skb_reserve(skb, PCH_GBE_DMA_ALIGN);
-		buffer_info->skb = skb;
+		buffer_info->skb = NULL;
 		tx_desc = PCH_GBE_TX_DESC(*tx_ring, i);
 		tx_desc->gbec_status = (DSC_INIT16);
 	}
@@ -1622,9 +1625,9 @@ pch_gbe_clean_tx(struct pch_gbe_adapter *adapter,
 					 buffer_info->length, DMA_TO_DEVICE);
 			buffer_info->mapped = false;
 		}
-		if (buffer_info->skb) {
-			pr_debug("trim buffer_info->skb : %d\n", i);
-			skb_trim(buffer_info->skb, 0);
+		if (skb) {
+			dev_kfree_skb_any(skb);
+			buffer_info->skb = NULL;
 		}
 		tx_desc->gbec_status = DSC_INIT16;
 		if (unlikely(++i == tx_ring->count))

RE: pch_gbe: dont-copy-payload (was [PATCH 1/4] ...)

[Eric Dumazet]

On Mon, 2012-08-06 at 07:19 -0700, Andy Cress wrote:
> I found out why the proposed dont-copy-payload patch didn't work with
> this pch_gbe NIC.
> This NIC PHY requires 64-byte-aligned DMA, and the transmit buffers
> won't be transferred if skb->data is not 64-byte-aligned.  Apparently
> the data copy has a by-product of aligning the buffers.  
> 
> I tried using skb_reserve(skb,64) in pch_gbe_alloc_tx_buffers and
> pch-gbe_alloc_rx_buffers, but that didn't seem to resolve it.
> 
> How can I make sure that the transmit data buffers are
> 64-byte-aligned?
> 

There is no support for such requirement in linux stacks.

Only solution for the driver is to copy all frames to 64-byte-aligned
bounce buffers.

RE: [PATCH 1/4] pch_gbe: fix the checksum fill to the error location

[Andy Cress]

Yes, this needs rework to use the standard routine.
Thanks for the input.

Andy

-----Original Message-----
From: Ben Hutchings [mailto:bhutchings@solarflare.com] 
Sent: Monday, July 09, 2012 4:16 PM
To: Andy Cress
Cc: netdev@vger.kernel.org
Subject: Re: [PATCH 1/4] pch_gbe: fix the checksum fill to the error location

On Mon, 2012-07-09 at 06:30 -0700, Andy Cress wrote:
> From: Zhong Hongbo <hongbo.zhong@windriver.com>
> Date: Mon, 9 Apr 2012 10:51:28 +0800
> 
[...]
>
> We can fix this issue by manually calculate the offset of the TCP
> checksum
>  and update it accordingly.
[...]

You should be using skb_checksum_start_offset() instead.

Ben.

Re: [PATCH 1/4] pch_gbe: fix the checksum fill to the error location

[Ben Hutchings]

On Mon, 2012-07-09 at 06:30 -0700, Andy Cress wrote:
> From: Zhong Hongbo <hongbo.zhong@windriver.com>
> Date: Mon, 9 Apr 2012 10:51:28 +0800
> 
> Due to some unknown hardware limitations the pch_gbe hardware cannot
> calculate checksums when the length of network package is less
> than 64 bytes, where we will surprisingly encounter a problem of
> the destination IP incorrectly changed.
> 
> When forwarding network packages at the network layer the IP packages
> won't be relayed to the upper transport layer and analyzed there,
> consequently, skb->transport_header pointer will be mistakenly remained
> the same as that of skb->network_header, resulting in TCP checksum
> wrongly
> filled into the field of destination IP in IP header.
>
> We can fix this issue by manually calculate the offset of the TCP
> checksum
>  and update it accordingly.
[...]

You should be using skb_checksum_start_offset() instead.

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

[PATCH 1/4] pch_gbe: fix the checksum fill to the error location

[Andy Cress]

From: Zhong Hongbo <hongbo.zhong@windriver.com>
Date: Mon, 9 Apr 2012 10:51:28 +0800

Due to some unknown hardware limitations the pch_gbe hardware cannot
calculate checksums when the length of network package is less
than 64 bytes, where we will surprisingly encounter a problem of
the destination IP incorrectly changed.

When forwarding network packages at the network layer the IP packages
won't be relayed to the upper transport layer and analyzed there,
consequently, skb->transport_header pointer will be mistakenly remained
the same as that of skb->network_header, resulting in TCP checksum
wrongly
filled into the field of destination IP in IP header.

We can fix this issue by manually calculate the offset of the TCP
checksum
 and update it accordingly.

Signed-off-by: Zhong Hongbo <hongbo.zhong@windriver.com>
Merged-by: Andy Cress <andy.cress@us.kontron.com>

---
 drivers/net/pch_gbe/pch_gbe_main.c |   14 ++++++++------
 1 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/drivers/net/ethernet/oki-semi/pch_gbe/pch_gbe_main.c
b/drivers/net/ethernet/oki-semi/pch_gbe/pch_gbe_main.c
index 3787c64..4c04843 100644
--- a/drivers/net/ethernet/oki-semi/pch_gbe/pch_gbe_main.c
+++ b/drivers/net/ethernet/oki-semi/pch_gbe/pch_gbe_main.c
@@ -1180,30 +1180,32 @@ static void pch_gbe_tx_queue(struct
pch_gbe_adapter *adapter,
 	 * when the received data size is less than 64 bytes.
 	 */
 	if (skb->len < PCH_GBE_SHORT_PKT && skb->ip_summed !=
CHECKSUM_NONE) {
+		struct iphdr *iph = ip_hdr(skb);
 		frame_ctrl |= PCH_GBE_TXD_CTRL_APAD |
 			      PCH_GBE_TXD_CTRL_TCPIP_ACC_OFF;
 		if (skb->protocol == htons(ETH_P_IP)) {
-			struct iphdr *iph = ip_hdr(skb);
 			unsigned int offset;
-			offset = skb_transport_offset(skb);
+			offset = (unsigned char *)((u8 *)iph + iph->ihl
* 4) - skb->data;
 			if (iph->protocol == IPPROTO_TCP) {
+				struct tcphdr *tcphdr_point = (struct
tcphdr *)((u8 *)iph + iph->ihl * 4);
 				skb->csum = 0;
-				tcp_hdr(skb)->check = 0;
+				tcphdr_point->check = 0;
 				skb->csum = skb_checksum(skb, offset,
 							 skb->len -
offset, 0);
-				tcp_hdr(skb)->check =
+				tcphdr_point->check = 
 					csum_tcpudp_magic(iph->saddr,
 							  iph->daddr,
 							  skb->len -
offset,
 							  IPPROTO_TCP,
 							  skb->csum);
 			} else if (iph->protocol == IPPROTO_UDP) {
+				struct udphdr *udphdr_point = (struct
udphdr *)((u8 *)iph + iph->ihl * 4);
 				skb->csum = 0;
-				udp_hdr(skb)->check = 0;
+				udphdr_point->check = 0;
 				skb->csum =
 					skb_checksum(skb, offset,
 						     skb->len - offset,
0);
-				udp_hdr(skb)->check =
+				udphdr_point->check = 
 					csum_tcpudp_magic(iph->saddr,
 							  iph->daddr,
 							  skb->len -
offset,