linux-kernel - Re: BUG: selftest/net/tun: Hang in unregister

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Date:   Thu, 16 Mar 2023 21:28:46 +0100
From:   Mirsad Goran Todorovac <mirsad.todorovac@....unizg.hr>
To:     Eric Dumazet <edumazet@...gle.com>,
        Kuniyuki Iwashima <kuniyu@...zon.com>
Cc:     davem@...emloft.net, kuba@...nel.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, netdev@...r.kernel.org,
        pabeni@...hat.com, shuah@...nel.org
Subject: Re: BUG: selftest/net/tun: Hang in unregister_netdevice

On 15. 03. 2023. 21:59, Eric Dumazet wrote:
> On Wed, Mar 15, 2023 at 1:57 PM Kuniyuki Iwashima <kuniyu@...zon.com> wrote:
>>
>> However, we don't assume the delay and also the failure in
>> tun_set_real_num_queues().
>>
>> In this case, we have to re-initialise the queues without
>> touching kobjects.
>>
>> Eric,
>> Are you working on this?
>> If not, let me try fixing this :)
> 
> I am not working on this, please go ahead, thanks !

Hi,

It's me again. I just have new findings.

[root@...mtodorov linux_torvalds]# grep -E '(KOBJECT|TRACKER)' /boot/config-6.3.0-rc2-00006-gfc89d7fb499b 
CONFIG_REF_TRACKER=y
CONFIG_NET_DEV_REFCNT_TRACKER=y
CONFIG_NET_NS_REFCNT_TRACKER=y
CONFIG_DEBUG_KOBJECT=y
# CONFIG_DEBUG_KOBJECT_RELEASE is not set
# CONFIG_SAMPLE_KOBJECT is not set
# CONFIG_TEST_REF_TRACKER is not set
[root@...mtodorov linux_torvalds]# uname -rms
Linux 6.3.0-rc2-00006-gfc89d7fb499b x86_64
[root@...mtodorov linux_torvalds]# grep -E '(KOBJECT|TRACKER)' /boot/config-6.3.0-rc2-00006-gfc89d7fb499b 
CONFIG_REF_TRACKER=y
CONFIG_NET_DEV_REFCNT_TRACKER=y
CONFIG_NET_NS_REFCNT_TRACKER=y
CONFIG_DEBUG_KOBJECT=y
# CONFIG_DEBUG_KOBJECT_RELEASE is not set
# CONFIG_SAMPLE_KOBJECT is not set
# CONFIG_TEST_REF_TRACKER is not set
[root@...mtodorov linux_torvalds]# tools/testing/selftests/net/tun
TAP version 13
1..5
# Starting 5 tests from 1 test cases.
#  RUN           tun.delete_detach_close ...
#            OK  tun.delete_detach_close
ok 1 tun.delete_detach_close
#  RUN           tun.detach_delete_close ...
#            OK  tun.detach_delete_close
ok 2 tun.detach_delete_close
#  RUN           tun.detach_close_delete ...
#            OK  tun.detach_close_delete
ok 3 tun.detach_close_delete
#  RUN           tun.reattach_delete_close ...
#            OK  tun.reattach_delete_close
ok 4 tun.reattach_delete_close
#  RUN           tun.reattach_close_delete ...
#            OK  tun.reattach_close_delete
ok 5 tun.reattach_close_delete
# PASSED: 5 / 5 tests passed.
# Totals: pass:5 fail:0 xfail:0 xpass:0 skip:0 error:0
[root@...mtodorov linux_torvalds]# 

My interpretation if you allow it is that the bug search can be narrowed to the code
that depends on CONFIG_DEBUG_KOBJECT_RELEASE=y.

Best regards,
Mirsad


CONFIG_DEBUG_KOBJECT=y alone doesn't seem to be sufficient to trigger the reference leak.

Hope this helps narrow down the search.

-- 
Mirsad Goran Todorovac
Sistem inženjer
Grafički fakultet | Akademija likovnih umjetnosti
Sveučilište u Zagrebu
 
System engineer
Faculty of Graphic Arts | Academy of Fine Arts
University of Zagreb, Republic of Croatia
The European Union