netdev - Re: 5.10.4+ hang with 'rmmod nf

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Date:   Fri, 8 Jan 2021 05:07:12 -0800
From:   Ben Greear <greearb@...delatech.com>
To:     Florian Westphal <fw@...len.de>
Cc:     netdev <netdev@...r.kernel.org>
Subject: Re: 5.10.4+ hang with 'rmmod nf_conntrack'

On 1/7/21 10:16 PM, Florian Westphal wrote:
> Ben Greear <greearb@...delatech.com> wrote:
>> I noticed my system has a hung process trying to 'rmmod nf_conntrack'.
>>
>> I've generally been doing the script that calls rmmod forever,
>> but only extensively tested on 5.4 kernel and earlier.
>>
>> If anyone has any ideas, please let me know.  This is from 'sysrq t'.  I don't see
>> any hung-task splats in dmesg.
> 
> rmmod on conntrack loops forever until the active conntrack object count reaches 0.
> (plus a walk of the conntrack table to evict/put all entries).
> 
>> I'll see if it is reproducible and if so will try
>> with lockdep enabled...
> 
> No idea, there was a regression in 5.6, but that was fixed by the time
> 5.7 was released.
> 
> Can't reproduce hangs with a script that injects a few dummy entries
> and then removes the module:
> 
> added=0
> 
> add_and_rmmod()
> {
>          while [ $added -lt 1000 ]; do
>                  conntrack -I -s $(($RANDOM%256)).$(($RANDOM%256)).$(($RANDOM%256)).$(($RANDOM%255+1)) \
>                          -d $(($RANDOM%256)).$(($RANDOM%256)).$(($RANDOM%256)).$(($RANDOM%255+1)) \
>                           --protonum 6 --timeout $(((RANDOM%120) + 240)) --state ESTABLISHED --sport $RANDOM --dport $RANDOM 2> /dev/null || break
> 
>                  added=$((added + 1))
>                  if [ $((added % 1000)) -eq 0 ];then
>                          echo $added
>                  fi
>          done
> 
>          echo rmmod after adding $added entries
>          conntrack -C
>          rmmod nf_conntrack_netlink
>          rmmod nf_conntrack
> }
> 
> add_and_rmmod
> 
> I don't see how it would make a difference, but do you have any special conntrack features enabled
> at run time, e.g. reliable netlink events? (If you don't know what I mean the answer is no).

Not that I know of, but I am using lots of VRF devices, each with their own routing table, as well
as some wifi stations and AP netdevs.

I'll let you know if I can reproduce it again..

Thanks,
Ben


-- 
Ben Greear <greearb@...delatech.com>
Candela Technologies Inc  http://www.candelatech.com