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Message-ID: <c1d15bd0-8b62-f7c0-0f2e-1d527827f451@roeck-us.net>
Date: Sun, 11 Apr 2021 14:32:50 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: Eric Dumazet <edumazet@...gle.com>
Cc: Eric Dumazet <eric.dumazet@...il.com>,
"David S . Miller" <davem@...emloft.net>,
Jakub Kicinski <kuba@...nel.org>,
netdev <netdev@...r.kernel.org>,
Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
"Michael S. Tsirkin" <mst@...hat.com>,
Jason Wang <jasowang@...hat.com>,
virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH net] virtio_net: Do not pull payload in skb->head
On 4/11/21 2:23 PM, Eric Dumazet wrote:
> On Sun, Apr 11, 2021 at 10:37 PM Guenter Roeck <linux@...ck-us.net> wrote:
>>
>> On 4/11/21 8:06 AM, Eric Dumazet wrote:
>>> On Sun, Apr 11, 2021 at 3:43 PM Guenter Roeck <linux@...ck-us.net> wrote:
>>>
>>>> This patch causes a virtio-net interface failure when booting sh4 images
>>>> in qemu. The test case is nothing special: Just try to get an IP address
>>>> using udhcpc. If it fails, udhcpc reports:
>>>>
>>>> udhcpc: started, v1.33.0
>>>> udhcpc: sending discover
>>>> FAIL
>>>>
>>>
>>> Can you investigate where the incoming packet is dropped ?
>>>
>>
>> Unless I am missing something, packets are not dropped. It looks more
>> like udhcpc gets bad indigestion in the receive path and exits immediately.
>> Plus, it doesn't happen all the time; sometimes it receives the discover
>> response and is able to obtain an IP address.
>>
>> Overall this is quite puzzling since udhcpc exits immediately when the problem
>> is seen, no matter which option I give it on the command line; it should not
>> really do that.
>
>
> Could you strace both cases and report differences you can spot ?
>
> strace -o STRACE -f -s 1000 udhcpc
>
I'll give it a try. It will take a while; I'll need to add strace to my root
file systems first.
As a quick hack, I added some debugging into the kernel; it looks like
the data part of the dhcp discover response may get lost with your patch
in place.
dhcp discover response with patch in place (bad):
virtio_net virtio0 eth0: __udp4_lib_rcv: data 0x8ca4cc44 head 0x8ca4cc00 tail 0x8ca4cc4c len 556 datalen 548 caller ip_protocol_deliver_rcu+0xac/0x178
00000000: 70 c1 a9 8c 00 00 00 00 00 00 00 00 20 ee c3 7b 34 00 e0 7b 08 00 00 00 00 00 00 00 00 00 00 00 p........... ..{4..{............
00000020: 60 c8 ff ff ff ff ff ff 52 55 0a 00 02 02 08 00 45 10 02 40 00 00 00 00 40 11 6c 9c 0a 00 02 02 `.......RU......E..@....@.......
00000040: ff ff ff ff 00 43 00 44 02 2c e1 21 00 00 00 00 f0 6f a4 7b 00 00 80 00 ff ff ff ff 7f 45 4c 46 .....C.D.,.!.....o.{.........ELF
^^ udp header
^^^^^ UDP length (556)
^^ start of UDP data (dhcp discover reply)
00000060: 01 01 01 00 00 00 00 00 00 00 00 00 02 00 2a 00 01 00 00 00 b0 6e 40 00 34 00 00 00 2c f6 0a 00 ..............*......n@.....,...
00000080: 17 00 00 00 34 00 20 00 08 00 28 00 16 00 15 00 06 00 00 00 34 00 00 00 34 00 40 00 34 00 40 00 ....4. ...(.........4...4.@.4.@.
000000a0: 00 01 00 00 00 01 00 00 04 00 00 00 04 00 00 00 03 00 00 00 34 01 00 00 34 01 40 00 34 01 40 00 ....................4...4.@.4.@.
000000c0: 15 00 00 00 15 00 00 00 04 00 00 00 01 00 00 00 01 00 00 00 00 00 00 00 00 00 40 00 00 00 40 00 ..........................@...@.
000000e0: 1c e2 0a 00 1c e2 0a 00 05 00 00 00 00 00 01 00 01 00 00 00 38 ef 0a 00 38 ef 4b 00 38 ef 4b 00 ....................8...8.K.8.K.
00000100: 00 00 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 01 00 00 00 ................................
00000120: b8 00 00 00 00 4c f9 8f 24 02 00 00 36 00 00 00 50 e5 74 64 88 e0 0a 00 88 e0 4a 00 88 e0 4a 00 .....L..$...6...P.td......J...J.
00000140: 2c 00 00 00 2c 00 00 00 04 00 00 00 04 00 00 00 51 e5 74 64 00 00 00 00 00 00 00 00 00 00 00 00 ,...,...........Q.td............
00000160: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................................
00000180: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................................
000001a0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................................
000001c0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................................
000001e0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................................
00000200: 1c 63 5a 8c 00 3e a4 8c 88 f9 50 8c 0c ce a4 8c 0c ce a4 8c 24 81 a1 8c 00 00 00 00 1c 5c 5a 8c .cZ..>....P.........$........\Z.
00000220: 04 b8 a5 8c 01 00 00 00 03 00 00 00 ............
dhcp discover response with patch reverted (ok):
virtio_net virtio0 eth0: __udp4_lib_rcv: data 0x8ca4ca44 head 0x8ca4ca00 tail 0x8ca4cb00 len 556 datalen 368 caller ip_protocol_deliver_rcu+0xac/0x178
^^^^^^^^^^ ^^^^^^^^^^ ^^^
00000000: 4c bd ab 8c 00 00 00 00 00 00 00 00 20 2e 85 7b 34 00 e0 7b 08 00 00 00 00 00 00 00 00 00 00 00 L........... ..{4..{............
00000020: 40 9a ff ff ff ff ff ff 52 55 0a 00 02 02 08 00 45 10 02 40 00 00 00 00 40 11 6c 9c 0a 00 02 02 @.......RU......E..@....@.......
^^^^^ ip length (576)
00000040: ff ff ff ff 00 43 00 44 02 2c 06 18 02 01 06 00 e6 fd ce 5b 00 00 00 00 00 00 00 00 0a 00 02 0f .....C.D.,.........[............
^^ udp header
^^^^^ UDP length (556)
^^ start of UDP data
00000060: 0a 00 02 02 00 00 00 00 52 54 00 12 34 56 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ........RT..4V..................
00000080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................................
000000a0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................................
000000c0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................................
000000e0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................................
00000100: 00 00 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 02 00 00 00 ................................
00000120: b8 00 00 00 00 4d f9 8f 70 01 00 00 ea 00 00 00 50 e5 74 64 88 e0 0a 00 88 e0 4a 00 88 e0 4a 00 .....M..p.......P.td......J...J.
00000140: 2c 00 00 00 2c 00 00 00 04 00 00 00 04 00 00 00 51 e5 74 64 00 00 00 00 00 00 00 00 00 00 00 00 ,...,...........Q.td............
00000160: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................................
00000180: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................................
000001a0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................................
000001c0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................................
000001e0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................................
00000200: 00 00 00 00 00 00 00 00 06 00 01 00 54 cc a4 8c 08 00 00 00 02 00 00 00 00 00 00 00 01 00 00 00 ............T...................
00000220: 08 00 00 00 00 00 00 00 14 cd a4 8c ............
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