netdev - Re: Regression: TCP connections fail over wireless: bad cksum?

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Message-ID: <CA+mtBx-5j0o6ZWhzXidLPG28ZnHBvSeCJ+hda5_hsu4Lq-_a=A@mail.gmail.com>
Date:	Thu, 4 Sep 2014 20:41:14 -0700
From:	Tom Herbert <therbert@...gle.com>
To:	Ted Percival <ted@...p.id.au>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Linux Netdev List <netdev@...r.kernel.org>
Subject: Re: Regression: TCP connections fail over wireless: bad cksum?

On Thu, Sep 4, 2014 at 4:21 PM, Ted Percival <ted@...p.id.au> wrote:
> On 09/04/2014 04:50 PM, Eric Dumazet wrote:
>> On Thu, 2014-09-04 at 14:11 -0600, Ted Percival wrote:
>>> Yesterday's linux-next build introduced a problem with wireless
>>> networking on my machine. ie. next-20140901 worked fine but
>>> next-20140902 does not seem able to sustain a TCP connection over
>>> wireless. Wired networking works fine. I am using the brcmsmac driver
>>> and the hardware is "Broadcom Corporation BCM4313 802.11b/g/n Wireless
>>> LAN Controller (rev 01)".
>>>
>>> Pings, even large pings (ping -s 16000) work fine but TCP connections hang.
>>>
>>> I looked through the changes between the bad & good commits from the net
>>> & net-next trees and I wonder if some of the changes to checksumming
>>> have surfaced a problem with this driver. When I look at a tcpdump, it
>>> indicates that all the checksums are wrong (although I don't know if
>>> that is just due to hardware offload).
>>>
>>> Here is a short trace of the hung connection attempt of
>>>   curl http://lwn.net/
>>>
>>> $ sudo tcpdump -vvn -i wlan0 port 80
>>> tcpdump: listening on wlan0, link-type EN10MB (Ethernet), capture size
>>> 65535 bytes
>>> 13:20:15.120770 IP (tos 0x0, ttl 64, id 22734, offset 0, flags [DF],
>>> proto TCP (6), length 60)
>>>     10.5.51.93.38035 > 72.51.34.34.80: Flags [S], cksum 0xa7e5
>>> (incorrect -> 0x4fac), seq 2861986597, win 29200, options [mss
>>> 1460,sackOK,TS val 142315 ecr 0,nop,wscale 7], length 0
>>> 13:20:16.121755 IP (tos 0x0, ttl 64, id 22735, offset 0, flags [DF],
>>> proto TCP (6), length 60)
>>>     10.5.51.93.38035 > 72.51.34.34.80: Flags [S], cksum 0xa7e5
>>> (incorrect -> 0x4bc3), seq 2861986597, win 29200, options [mss
>>> 1460,sackOK,TS val 143316 ecr 0,nop,wscale 7], length 0
>>> 13:20:18.125748 IP (tos 0x0, ttl 64, id 22736, offset 0, flags [DF],
>>> proto TCP (6), length 60)
>>>     10.5.51.93.38035 > 72.51.34.34.80: Flags [S], cksum 0xa7e5
>>> (incorrect -> 0x43ef), seq 2861986597, win 29200, options [mss
>>> 1460,sackOK,TS val 145320 ecr 0,nop,wscale 7], length 0
>>> 13:20:22.133743 IP (tos 0x0, ttl 64, id 22737, offset 0, flags [DF],
>>> proto TCP (6), length 60)
>>>     10.5.51.93.38035 > 72.51.34.34.80: Flags [S], cksum 0xa7e5
>>> (incorrect -> 0x3447), seq 2861986597, win 29200, options [mss
>>> 1460,sackOK,TS val 149328 ecr 0,nop,wscale 7], length 0
>>> 13:20:30.149754 IP (tos 0x0, ttl 64, id 22738, offset 0, flags [DF],
>>> proto TCP (6), length 60)
>>>     10.5.51.93.38035 > 72.51.34.34.80: Flags [S], cksum 0xa7e5
>>> (incorrect -> 0x14f7), seq 2861986597, win 29200, options [mss
>>> 1460,sackOK,TS val 157344 ecr 0,nop,wscale 7], length 0
>>>
>>>
>>> I don't see anything that looks related in dmesg. The only brcmsmac
>>> messages I see are:
>>>
>>> [  567.122218] brcmsmac bcma0:0: brcmsmac: brcms_ops_bss_info_changed:
>>> associated
>>> [  567.122226] brcmsmac bcma0:0: brcms_ops_bss_info_changed: arp
>>> filtering: 1 addresses (implement)
>>> [  567.122231] brcmsmac bcma0:0: brcms_ops_bss_info_changed: qos
>>> enabled: true (implement)
>>> [  567.192283] brcmsmac bcma0:0: brcms_ops_bss_info_changed: qos
>>> enabled: true (implement)
>>>
>>> I am writing to linux-netdev rather than linux-wireless because
>>> according to Next/SHA1s the wireless & wireless-next trees were not
>>> updated between next-20140901 and next-20140902, but the net & net-next
>>> trees were updated, so maybe the regression came from there. (I haven't
>>> tested next-20140903 because it won't boot for unrelated reasons.)
>>>
>>> Let me know if I should just file this in Bugzilla or what information I
>>> can provide to help track this down, if it hasn't already been identified.
>>>
>>> The here are the good (-) and bad (+) trees from Next/SHA1s at the
>>> next-* tags mentioned earlier that I built from.
>>>
>>> -net            38ab1fa981d543e1b00f4ffbce4ddb480cd2effe
>>> +net            cc25f0cbe4409d6a573b1f3bf7020d5b04076ee9
>>>
>>> -net-next       dace1b54726bffe1c009f7661e3cee6b762f30c8
>>> +net-next       364a9e93243d1785f310c0964af0e24bf1adac03
>>>
>>
>> Could you post
>>
>> ethtool -k wlan0
>>
>> And try
>>
>> ethtool -K wlan tx off
>
> # ethtool -k wlan0
> Features for wlan0:
> rx-checksumming: off [fixed]
> tx-checksumming: off
>         tx-checksum-ipv4: off [fixed]
>         tx-checksum-ip-generic: off [fixed]
>         tx-checksum-ipv6: off [fixed]
>         tx-checksum-fcoe-crc: off [fixed]
>         tx-checksum-sctp: off [fixed]
> scatter-gather: off
>         tx-scatter-gather: off [fixed]
>         tx-scatter-gather-fraglist: off [fixed]
> tcp-segmentation-offload: off
>         tx-tcp-segmentation: off [fixed]
>         tx-tcp-ecn-segmentation: off [fixed]
>         tx-tcp6-segmentation: off [fixed]
> udp-fragmentation-offload: off [fixed]
> generic-segmentation-offload: off [requested on]
> generic-receive-offload: on
> large-receive-offload: off [fixed]
> rx-vlan-offload: off [fixed]
> tx-vlan-offload: off [fixed]
> ntuple-filters: off [fixed]
> receive-hashing: off [fixed]
> highdma: off [fixed]
> rx-vlan-filter: off [fixed]
> vlan-challenged: off [fixed]
> tx-lockless: off [fixed]
> netns-local: on [fixed]
> tx-gso-robust: off [fixed]
> tx-fcoe-segmentation: off [fixed]
> tx-gre-segmentation: off [fixed]
> tx-ipip-segmentation: off [fixed]
> tx-sit-segmentation: off [fixed]
> tx-udp_tnl-segmentation: off [fixed]
> tx-mpls-segmentation: off [fixed]
> fcoe-mtu: off [fixed]
> tx-nocache-copy: off
> loopback: off [fixed]
> rx-fcs: off [fixed]
> rx-all: off [fixed]
> tx-vlan-stag-hw-insert: off [fixed]
> rx-vlan-stag-hw-parse: off [fixed]
> rx-vlan-stag-filter: off [fixed]
> l2-fwd-offload: off [fixed]
> busy-poll: off [fixed]
>
> # ethtool -K wlan0 tx off
> Cannot change tx-checksumming
>
> I will try to isolate the commit that caused the regression.

Please provide 'netstat -s' to see if bad checksums are being
reported. Also, try disabling GRO to see the effect.

Thanks,
Tom

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