Guenter Roeck
2021-Apr-11 21:32 UTC
[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 at roeck-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 at roeck-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.. at ....@.l..... 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 at .4...,... 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. at .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. at .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 .......................... at ...@. 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.. at ....@.l..... ^^^^^ 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 ............