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

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Date:   Tue, 14 Mar 2023 12:45:03 +0100
From:   Mirsad Todorovac <mirsad.todorovac@....unizg.hr>
To:     netdev@...r.kernel.org, linux-kselftest@...r.kernel.org
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, Shuah Khan <shuah@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        linux-kernel@...r.kernel.org
Subject: BUG: selftest/net/tun: Hang in unregister_netdevice

Hi, all!

After running tools/testing/selftests/net/tun, there seems to be some kind of hang
in test "FAIL  tun.reattach_delete_close" or "FAIL  tun.reattach_close_delete".

Two tests exit by timeout, but the processes left are unkillable, even with kill -9 PID:

[root@...mtodorov linux_torvalds]# ps -ef | grep tun
root        1140       1  0 12:16 ?        00:00:00 /bin/bash /usr/sbin/ksmtuned
root        1333       1  0 12:16 ?        00:00:01 /usr/libexec/platform-python -Es /usr/sbin/tuned -l -P
root        3930    2309  0 12:20 pts/1    00:00:00 tools/testing/selftests/net/tun
root        3952    2309  0 12:21 pts/1    00:00:00 tools/testing/selftests/net/tun
root        4056    3765  0 12:25 pts/1    00:00:00 grep --color=auto tun
[root@...mtodorov linux_torvalds]# kill -9 3930 3952
[root@...mtodorov linux_torvalds]# ps -ef | grep tun
root        1140       1  0 12:16 ?        00:00:00 /bin/bash /usr/sbin/ksmtuned
root        1333       1  0 12:16 ?        00:00:01 /usr/libexec/platform-python -Es /usr/sbin/tuned -l -P
root        3930    2309  0 12:20 pts/1    00:00:00 tools/testing/selftests/net/tun
root        3952    2309  0 12:21 pts/1    00:00:00 tools/testing/selftests/net/tun
root        4060    3765  0 12:25 pts/1    00:00:00 grep --color=auto tun
[root@...mtodorov linux_torvalds]#

The kernel seems to be stuck in some loop, and filling the log with the
following messages until reboot, where it is also waiting very long on the
situation to timeout, which apparently never happens.

Mar 14 11:54:09 pc-mtodorov kernel: unregister_netdevice: waiting for tap0 to become free. Usage count = 3
Mar 14 11:54:19 pc-mtodorov kernel: unregister_netdevice: waiting for tap0 to become free. Usage count = 3
Mar 14 11:54:29 pc-mtodorov kernel: unregister_netdevice: waiting for tap0 to become free. Usage count = 3
Mar 14 11:54:40 pc-mtodorov kernel: unregister_netdevice: waiting for tap0 to become free. Usage count = 3
Mar 14 11:54:50 pc-mtodorov kernel: unregister_netdevice: waiting for tap0 to become free. Usage count = 3

The platform is kernel 6.3.0-rc2 on AlmaLinux 8.7 and a LENOVO_MT_10TX_BU_Lenovo_FM_V530S-07ICB
(lshw output attached).

The .config is here:

https://domac.alu.hr/~mtodorov/linux/selftests/net-tun/config-6.3.0-rc2-mg-andy-devres-00006-gfc89d7fb499b

Basically, it is a vanilla Torvalds tree kernel with MGLRU, KMEMLEAK, and CONFIG_DEBUG_KOBJECT enabled.
And devres patch.

Please find the strace of the net/tun run attached.

I am available for additional diagnostics.

Hope this helps.

Best regards,
Mirsad

-- 
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
View attachment "tun-log.txt" of type "text/plain" (7052 bytes)

View attachment "lshw-lenovo-desktop.txt" of type "text/plain" (23889 bytes)