Re: [PATCH v1 3/5] dpkg: Remove unmount loop

[Anton Mikanovich <amikan@ilbers.de>]

08.07.2021 15:21, Jan Kiszka wrote:
> On 07.07.21 18:38, Anton Mikanovich wrote:
>> Remove while loop when trying to unmount WORKDIR. Any failures of
>> umount should be investigated to fix the root cause.
>> Also make dpkg_undo_mounts do not fail if dpkg_do_mounts was not
>> called or it was called twice.
>>
> This is very likely wrong: We know from the past (should be in the git
> history, e.g 17d0842d) that not all subprocesses started inside the
> chroot may have been terminated when we left it. That can cause
> significant delays between returning from chroot and finding non-busy
> mount points to complete all umounts. Now, if you silently fail umounts,
> you may find inconsistently mounted chroots on the next recipe that
> tries to remount them. Big fat warning sign...!
>
> Jan

We've reproduced the issue fixed by 17d0842d on the old code (pre-17d0842d).
The issue was caused by unmounting buildchroot mounts without care of 
their usage.
The latest v5 patchset is not affected, because there is no global task 
fail handling, and per-task unmount is protected by the reference counting.

Moreover, buildchroot_undo_mounts was moved after the while loop in 
dpkg_undo_mounts in v5, so it will not fail immediately like we had it 
with '/sys/fs/cgroups is busy' failures (the real fix of 
'/sys/fs/cgroups is busy' is still in progress).

-- 
Anton Mikanovich
Promwad Ltd.
External service provider of ilbers GmbH
Maria-Merian-Str. 8
85521 Ottobrunn, Germany
+49 (89) 122 67 24-0
Commercial register Munich, HRB 214197
General Manager: Baurzhan Ismagulov