Date:   Thu, 29 Oct 2020 13:20:00 -0400
From:   Vishwanath Pai <vpai@...mai.com>
To:     Yunsheng Lin <linyunsheng@...wei.com>,
        Cong Wang <xiyou.wangcong@...il.com>
Cc:     "Hunt, Joshua" <johunt@...mai.com>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Jiri Pirko <jiri@...nulli.us>,
        David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "linuxarm@...wei.com" <linuxarm@...wei.com>,
        John Fastabend <john.fastabend@...il.com>,
        Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCH v2 net] net: sch_generic: aviod concurrent reset and
 enqueue op for lockless qdisc

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@...mai.com> 
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@...ntu) (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.

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