Re: [PATCH v2 net] net: sch_generic: aviod concurrent reset and enqueue op for lockless qdisc

[Yunsheng Lin]

On 2020/10/30 1:20, Vishwanath Pai wrote:
> On 10/29/20 6:24 AM, Yunsheng Lin wrote:
>> On 2020/10/29 12:50, Vishwanath Pai wrote:
>>> On 10/28/20 10:37 PM, Yunsheng Lin wrote:
>>>> On 2020/10/29 4:04, Vishwanath Pai wrote:
>>>>> On 10/28/20 1:47 PM, Cong Wang wrote:
>>>>>> On Wed, Oct 28, 2020 at 8:37 AM Pai, Vishwanath <vpai@xxxxxxxxxx> wrote:
>>>>>>> Hi,
>>>>>>>
>>>>>>> We noticed some problems when testing the latest 5.4 LTS kernel and traced it
>>>>>>> back to this commit using git bisect. When running our tests the machine stops
>>>>>>> responding to all traffic and the only way to recover is a reboot. I do not see
>>>>>>> a stack trace on the console.
>>>>>>
>>>>>> Do you mean the machine is still running fine just the network is down?
>>>>>>
>>>>>> If so, can you dump your tc config with stats when the problem is happening?
>>>>>> (You can use `tc -s -d qd show ...`.)
>>>>>>
>>>>>>>
>>>>>>> This can be reproduced using the packetdrill test below, it should be run a
>>>>>>> few times or in a loop. You should hit this issue within a few tries but
>>>>>>> sometimes might take up to 15-20 tries.
>>>>>> ...
>>>>>>> I can reproduce the issue easily on v5.4.68, and after reverting this commit it
>>>>>>> does not happen anymore.
>>>>>>
>>>>>> This is odd. The patch in this thread touches netdev reset path, if packetdrill
>>>>>> is the only thing you use to trigger the bug (that is netdev is always active),
>>>>>> I can not connect them.
>>>>>>
>>>>>> Thanks.
>>>>>
>>>>> Hi Cong,
>>>>>
>>>>>> Do you mean the machine is still running fine just the network is down?
>>>>>
>>>>> I was able to access the machine via serial console, it looks like it is
>>>>> up and running, just that networking is down.
>>>>>
>>>>>> If so, can you dump your tc config with stats when the problem is happening?
>>>>>> (You can use `tc -s -d qd show ...`.)
>>>>>
>>>>> If I try running tc when the machine is in this state the command never
>>>>> returns. It doesn't print anything but doesn't exit either.
>>>>>
>>>>>> This is odd. The patch in this thread touches netdev reset path, if packetdrill
>>>>>> is the only thing you use to trigger the bug (that is netdev is always active),
>>>>>> I can not connect them.
>>>>>
>>>>> I think packetdrill creates a tun0 interface when it starts the
>>>>> test and tears it down at the end, so it might be hitting this code path
>>>>> during teardown.
>>>>
>>>> Hi, Is there any preparation setup before running the above packetdrill test
>>>> case, I run the above test case in 5.9-rc4 with this patch applied without any
>>>> preparation setup, did not reproduce it.
>>>>
>>>> By the way, I am newbie to packetdrill:), it would be good to provide the
>>>> detail setup to reproduce it,thanks.
>>>>
>>>>>
>>>>> P.S: My mail server is having connectivity issues with vger.kernel.org
>>>>> so messages aren't getting delivered to netdev. It'll hopefully get
>>>>> resolved soon.
>>>>>
>>>>> Thanks,
>>>>> Vishwanath
>>>>>
>>>>>
>>>>> .
>>>>>
>>>
>>> I can't reproduce it on v5.9-rc4 either, it is probably an issue only on
>>> 5.4 then (and maybe older LTS versions). Can you give it a try on
>>> 5.4.68?
>>>
>>> For running packetdrill, download the latest version from their github
>>> repo, then run it in a loop without any special arguments. This is what
>>> I do to reproduce it:
>>>
>>> while true; do ./packetdrill <test-file>; done
>>>
>>> I don't think any other setup is necessary.
>>
>> Hi, run the above test for above an hour using 5.4.68, still did not
>> reproduce it, as below:
>>
>>
>> root@(none)$ cd /home/root/
>> root@(none)$ ls
>> creat_vlan.sh  packetdrill    test.pd
>> root@(none)$ cat test.pd
>> 0 `echo 4 > /proc/sys/net/ipv4/tcp_min_tso_segs`
>>
>> 0.400 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
>> 0.400 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
>>
>> // set maxseg to 1000 to work with both ipv4 and ipv6
>> 0.500 setsockopt(3, SOL_TCP, TCP_MAXSEG, [1000], 4) = 0
>> 0.500 bind(3, ..., ...) = 0
>> 0.500 listen(3, 1) = 0
>>
>> // Establish connection
>> 0.600 < S 0:0(0) win 32792 <mss 1000,sackOK,nop,nop,nop,wscale 5>
>> 0.600 > S. 0:0(0) ack 1 <...>
>>
>> 0.800 < . 1:1(0) ack 1 win 320
>> 0.800 accept(3, ..., ...) = 4
>>
>> // Send 4 data segments.
>> +0 write(4, ..., 4000) = 4000
>> +0 > P. 1:4001(4000) ack 1
>>
>> // Receive a SACK
>> +.1 < . 1:1(0) ack 1 win 320 <sack 1001:2001,nop,nop>
>>
>> +.3 %{ print "TCP CA state: ",tcpi_ca_state  }%
>> root@(none)$ cat creat_vlan.sh
>> #!/bin/sh
>>
>> for((i=0; i<10000; i++))
>> do
>>     ./packetdrill test.pd
>> done
>> root@(none)$ ./creat_vlan.sh
>> TCP CA state:  3
>> ^C
>> root@(none)$ ifconfig
>> eth0      Link encap:Ethernet  HWaddr 5c:e8:83:0d:f7:ed
>>           inet addr:192.168.1.93  Bcast:192.168.1.255 Mask:255.255.255.0
>>           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
>>           RX packets:3570 errors:0 dropped:0 overruns:0 frame:0
>>           TX packets:3190 errors:0 dropped:0 overruns:0 carrier:0
>>           collisions:0 txqueuelen:1000
>>           RX bytes:1076349 (1.0 MiB)  TX bytes:414874 (405.1 KiB)
>>
>> eth2      Link encap:Ethernet  HWaddr 5c:e8:83:0d:f7:ec
>>           inet addr:192.168.100.1  Bcast:192.168.100.255 Mask:255.255.255.0
>>           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
>>           RX packets:81848576 errors:0 dropped:0 overruns:0 frame:78
>>           TX packets:72497816 errors:0 dropped:0 overruns:0 carrier:0
>>           collisions:0 txqueuelen:1000
>>           RX bytes:2044282289568 (1.8 TiB)  TX bytes:2457441698852 (2.2 TiB)
>>
>> lo        Link encap:Local Loopback
>>           inet addr:127.0.0.1  Mask:255.0.0.0
>>           UP LOOPBACK RUNNING  MTU:65536  Metric:1
>>           RX packets:1 errors:0 dropped:0 overruns:0 frame:0
>>           TX packets:1 errors:0 dropped:0 overruns:0 carrier:0
>>           collisions:0 txqueuelen:1000
>>           RX bytes:68 (68.0 B)  TX bytes:68 (68.0 B)
>>
>> root@(none)$ ./creat_vlan.sh
>> TCP CA state:  3
>> TCP CA state:  3
>> TCP CA state:  3
>> TCP CA state:  3
>> TCP CA state:  3
>> TCP CA state:  3
>> TCP CA state:  3
>> TCP CA state:  3
>> TCP CA state:  3
>> TCP CA state:  3
>> TCP CA state:  3
>> TCP CA state:  3
>> TCP CA state:  3
>> TCP CA state:  3
>> TCP CA state:  3
>> TCP CA state:  3
>> TCP CA state:  3
>> TCP CA state:  3
>> TCP CA state:  3
>> TCP CA state:  3
>> ^C
>> root@(none)$ cat /proc/cmdline
>> BOOT_IMAGE=/linyunsheng/Image.5.0 rdinit=/init console=ttyAMA0,115200 earlycon=pl011,mmio32,0x94080000 iommu.strict=1
>> root@(none)$ cat /proc/version
>> Linux version 5.4.68 (linyunsheng@ubuntu) (gcc version 5.4.0 20160609 (Ubuntu/Linaro 5.4.0-6ubuntu1~16.04.12)) #1 SMP PREEMPT Thu Oct 29 16:59:37 CST 2020
>> root@(none)$
>>
>>
>>
>>>
>>> -Vishwanath
>>>
>>> .
>>>
> I couldn't get it to reproduce on a ubuntu VM, maybe something is
> different with the way we setup our machines. We do have some scripts in
> /etc/network/{if-up.d,if-post-down.d} etc, or probably something else.
> I'll let you know when I can reliably reproduce it on the VM.

Hi, Vishwanath
    Please see if the patch in the below link fix your problem, thanks.
https://www.spinics.net/lists/netdev/msg695908.html

> 
> .
>