Recursive mounts with kAFS, but not with OpenAFS

[Jan Henrik Sylvester]

On 6/13/24 01:26, Jeffrey E Altman wrote:
> On 5/4/2024 5:04 PM, Jeffrey Altman wrote:
>> On May 3, 2024, at 6:20 AM, Jan Henrik Sylvester 
>> <jan.henrik.sylvester at uni-hamburg.de> wrote:
>>> and a simple execution of find on a home directory had a machine hang 
>>> by the oom-killer killing vital system processes, because kAFS can go 
>>> more than a 1000 levels recursively into ~/AFSBAK/AFSBAK/AFSBAK...
>> Markus Suvanto reported the same problem on Feb 20th.   At the time 
>> Marc Dionne developed a patch to prevent the evaluation of a mount 
>> point to a volume name with the “.backup” extension from a volume of 
>> type AFSVL_BACKVOL.   Testing of the patch wasn’t complete so it did 
>> not get submitted.   Hopefully Marc can submit it next week.   Once 
>> merged by Linus it can be back ported to the actively maintained 
>> stable kernels.
>>> The volume user is mounted to 
>>> /afs/math.uni-hamburg.de/users/area/user and user.backup is mounted 
>>> to /afs/math.uni-hamburg.de/users/area/user/AFSBAK. Should 
>>> /afs/math.uni-hamburg.de/users/area/user/AFSBAK/AFSBAK automatically 
>>> be a mount point?
>> It's a mount point but should not be traversed.
> 
> Marc's patch has been merged into upstream and Greg has queued the patch 
> for inclusion in the next 6.9, 6.6, 6.1, 5.15, 5.10, and 5.4 stable 
> releases.  Most likely 6.9.5, 6.6.34, 6.1.94, 5.15.161, 5.10.218, 
> 5.4.278.  The patch will be available in the distros when they update to 
> one of those kernels or a later release.
> 
> You can file a bug report report against Ubuntu 24.04 and reference that 
> the bug has been fixed by commit 
> 29be9100aca2915fab54b5693309bc42956542e5 upstream.

Thanks a lot for your effort. Today, Ubuntu 24.04 got kernel 6.8.0-44 
including:

- afs: Don't cross .backup mountpoint from backup volume

> We hope that kafs meets the needs of your end users.

Unfortunately in our testing with Ubuntu 24.04, we have found more cases 
of problems with kAFS that we do not have with OpenAFS. Changing network 
conditions seem to be more of a problem for kAFS to recover from than 
for OpenAFS. Sorry, this is very vague for now. We will investigate kAFS 
further on testing machines and hope to come up with more specific bug 
reports (and on a new thread).

Best wishes,
Jan Henrik


-- 
Jan Henrik Sylvester <jan.henrik.sylvester at uni-hamburg.de>
Universität Hamburg / Fachbereich Mathematik / IT-Gruppe
Bundesstraße 55 (Geomatikum), 20146 Hamburg
Raum: 112, Tel.: +49-40-42838-5123 / +49-151-25350224
https://www.math.uni-hamburg.de/personen/sylvester/