linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Ben Dooks <ben.dooks@codethink.co.uk>
To: netdev@vger.kernel.org
Cc: oneukum@suse.com, davem@davemloft.net, linux-usb@vger.kernel.org,
	linux-kernel@vger.kernel.org, steve.glendinning@shawell.net,
	linux-kernel@lists.codethink.co.uk,
	Ben Dooks <ben.dooks@codethink.co.uk>
Subject: [PATCH 4/4] usbnet: smsc95xx: check for csum being in last four bytes
Date: Wed, 14 Nov 2018 11:50:22 +0000	[thread overview]
Message-ID: <20181114115022.9584-5-ben.dooks@codethink.co.uk> (raw)
In-Reply-To: <20181114115022.9584-1-ben.dooks@codethink.co.uk>

The manual states that the checksum cannot lie in the last DWORD of the
transmission, so add a basic check for this and fall back to software
checksumming the packet.

This only seems to trigger for ACK packets with no options or data to
return to the other end, and the use of the tx-alignment option makes
it more likely to happen.

Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
---
Fixes for v2:
- Fix spelling of check at Sergei's suggestion
- Move skb->len check into smsc95xx_can_tx_checksum()
- Change name of smsc95xx_can_checksum to explicitly say it is tx-csum
---
 drivers/net/usb/smsc95xx.c | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/drivers/net/usb/smsc95xx.c b/drivers/net/usb/smsc95xx.c
index 8f7c473f3260..cc78ef78cc93 100644
--- a/drivers/net/usb/smsc95xx.c
+++ b/drivers/net/usb/smsc95xx.c
@@ -1997,6 +1997,23 @@ static u32 smsc95xx_calc_csum_preamble(struct sk_buff *skb)
 	return (high_16 << 16) | low_16;
 }
 
+/* The TX CSUM won't work if the checksum lies in the last 4 bytes of the
+ * transmission. This is fairly unlikely, only seems to trigger with some
+ * short TCP ACK packets sent.
+ *
+ * Note, this calculation should probably check for the alignment of the
+ * data as well, but a straight check for csum being in the last four bytes
+ * of the packet should be ok for now.
+*/
+static bool smsc95xx_can_tx_checksum(struct sk_buff *skb)
+{
+       unsigned int len = skb->len - skb_checksum_start_offset(skb);
+
+       if (skb->len <= 45)
+	       return false;
+       return skb->csum_offset < (len - (4 + 1));
+}
+
 static struct sk_buff *smsc95xx_tx_fixup(struct usbnet *dev,
 					 struct sk_buff *skb, gfp_t flags)
 {
@@ -2021,7 +2038,7 @@ static struct sk_buff *smsc95xx_tx_fixup(struct usbnet *dev,
 	tx_cmd_a = tx_cmd_b | TX_CMD_A_FIRST_SEG_ | TX_CMD_A_LAST_SEG_;
 
 	if (csum) {
-		if (skb->len <= 45) {
+		if (!smsc95xx_can_tx_checksum(skb)) {
 			/* workaround - hardware tx checksum does not work
 			 * properly with extremely small packets */
 			long csstart = skb_checksum_start_offset(skb);
-- 
2.19.1


  parent reply	other threads:[~2018-11-14 11:50 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-14 11:50 SMSC95xx driver updates (round 1) Ben Dooks
2018-11-14 11:50 ` [PATCH 1/4] usbnet: smsc95xx: fix rx packet alignment Ben Dooks
2018-11-14 11:50 ` [PATCH 2/4] usbnet: smsc95xx: simplify tx_fixup code Ben Dooks
2018-11-14 11:50 ` [PATCH 3/4] usbnet: smsc95xx: fix memcpy for accessing rx-data Ben Dooks
2018-11-14 11:50 ` Ben Dooks [this message]
2018-11-14 15:59   ` [PATCH 4/4] usbnet: smsc95xx: check for csum being in last four bytes Sergei Shtylyov
2018-11-14 11:58 ` SMSC95xx driver updates (round 1) Oliver Neukum
2018-11-15 18:06 ` Woojung.Huh
2018-11-16 10:49   ` Ben Dooks
2018-11-17  4:16 ` David Miller

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20181114115022.9584-5-ben.dooks@codethink.co.uk \
    --to=ben.dooks@codethink.co.uk \
    --cc=davem@davemloft.net \
    --cc=linux-kernel@lists.codethink.co.uk \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-usb@vger.kernel.org \
    --cc=netdev@vger.kernel.org \
    --cc=oneukum@suse.com \
    --cc=steve.glendinning@shawell.net \
    --subject='Re: [PATCH 4/4] usbnet: smsc95xx: check for csum being in last four bytes' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
on how to clone and mirror all data and code used for this inbox