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

[Vishwanath Pai]

On 11/2/20 4:08 AM, Yunsheng Lin wrote:
> 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://urldefense.com/v3/__https://www.spinics.net/lists/netdev/msg695908.html__;!!GjvTz_vk!Gc1MbfkLP7lWuWFxK2Bauofrqq53Tt79VJaozx08T8cmH0dRxAXuilS7xFt0$ 

>
>>
>> .
>>

I tried out the patch on top of 5.4.71 and it fixes the issue for me
too. Thanks for the quick fix.

- Vishwanath