Re: [PATCH 0/3] umount fixes and cleanups

[Jan Kiszka <jan.kiszka@siemens.com>]

On 05.12.18 15:26, Maxim Yu. Osipov wrote:
> On 12/5/18 3:14 PM, Jan Kiszka wrote:
>> On 05.12.18 12:12, Maxim Yu. Osipov wrote:
>>> On 12/5/18 12:29 PM, Jan Kiszka wrote:
>>>> Patches related to resolving the pending CI issues as well as
>>>> simplifying the umounts used during cleanup.
>>>
>>> Tried to run in patch queue:
>>>
>>> 027b7cf Remove redundant recursive umounts
>>> c1bdc33 isar-events: Improve umount handler
>>> b354273 ci: Wait for bitbake worker to finish before deleting artifacts
>>> 9cf29e6 isar-bootstrap: Fix and cleanup bind mounting
>>> b354026 isar-image: umount base-apt when doing offline build
>>> e965c0d gitlab-ci: Switch to ci_build.sh
>>> ...
>>>
>>> After execution of problematic test case (I rebooted PC and executed steps in 
>>> clean tree):
>>>
>>> my stretch Debian system was entered into unusable state
>>> as many important mounts were disappeared (see log of mount points
>>> before and after execution  of last command attached).
>>
>> OK, so I took the time and extracted the root cause. We may see a Debian 4.9 
>> kernel bug here:
>>
>> # mkdir my-mnt
>> # mount --rbind /sys my-mnt
>> # mount --make-rslave my-mnt
>> # umount {-R,-l,-R -l} my-mnt
>> # rmdir my-mnt
>> rmdir: failed to remove 'my-mnt': Device or resource busy
>>
>> This works fine on my Leap 15.0 kernel (4.12) as well as the 4.4 kernel 
>> (Ubuntu) used on our CI server.
> 
> This also works fine on my Debian 4.9 kernel (I've ran this sequence for every 
> combination of {-R, -l , -R -l}):
> 
>> root@tiberius:~# uname -a
>> Linux tiberius 4.9.0-8-amd64 #1 SMP Debian 4.9.110-3+deb9u6 (2018-10-08) 
>> x86_64 GNU/Linux

Hmpf, rechecking... I was still on 3.16 from the jessie that I upgraded from. 
Works fine with 4.9, indeed.

>> root@tiberius:~# mkdir my-mnt
>> root@tiberius:~# mount --rbind /sys my-mnt
>> root@tiberius:~# mount --make-rslave my-mnt
>> root@tiberius:~# umount -R my-mnt/
>> root@tiberius:~# rmdir my-mnt/
>> root@tiberius:~# mkdir my-mnt
>> root@tiberius:~# mount --rbind /sys my-mnt
>> root@tiberius:~# mount --make-rslave my-mnt
>> root@tiberius:~# umount -l my-mnt
>> root@tiberius:~# rmdir my-mnt/
>> root@tiberius:~# mkdir my-mnt
>> root@tiberius:~# mount --rbind /sys my-mnt
>> root@tiberius:~# mount --make-rslave my-mnt
>> root@tiberius:~# umount -R -l my-mnt
>> root@tiberius:~# rmdir my-mnt/
>> root@tiberius:~# 
> 

OK, then bind-mounting itself likely not the root cause, and we need to dig further.

Jan

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