Container backup frozen at snapshot due to sshfs mount [bug?]

[derbroti]

Hi,

First of all, I know it is not recommended but I feel like my scenario should work?

EDIT:
Ok, ventured into the bowels of the beast and I am very close to the issue.
In https://github.com/proxmox/pve-container/blob/master/src/PVE/LXC.pm#L1218 all mount points are send somewhere?
My dirty little hack is now to simply strip sshfs from the list before it gets send:

$mountdata =~ s/.*fuse.sshfs.*\n//g;

It works but I still have no clue what the issue is, as I do not speak perl, I fail to trace where this mounts list is send to.
I mean, I see it is a process inside the container? but said container is frozen, so I can not poke there... (see my reply).

I have an lxc container on pve 7.1-8 with a separate mount point:

local-zfs:subvol-107-disk-1,mp=/ext,size=1G

and disabled backups on it.
I have mounted an sshfs share inside the container into /ext/sshfs.

I use snapshots as backup mode onto a pbs.

Creating a backup stalls indefinitely trying to create a snapshot:

INFO: create storage snapshot 'vzdump'

/ext is excluded:

INFO: including mount point rootfs ('/') in backup
INFO: excluding volume mount point mp0 ('/ext') from backup (disabled)

and due to /ext being a separate mount point it is a separate zfs dataset:

rpool/data/subvol-107-disk-0  3.38G  1.62G     3.38G  /rpool/data/subvol-107-disk-0
rpool/data/subvol-107-disk-1    96K  1024M       96K  /rpool/data/subvol-107-disk-1

so how can vzdump freeze if it is not even supposed to touch /ext?

(I have tried several no-cache options for sshfs:

cache=no,noauto_cache,entry_timeout=0

but nothing worked).

So, besides it not being recommended, shouldn't this work?
I feel like this is a bug in vzdump as it seems it is not leaving my mountpoint alone?

Thanks for any feedback!

 

[derbroti]

Continuing to edit my post will probably never approve it, so a response:
A bit deeper, well only a few lines up... we have "do_syncfs".

Following that, the culprit is https://github.com/proxmox/pve-common/blob/master/src/PVE/Tools.pm#L1501 a simple sysopen.

What I do not understand is: running this manually inside the container works fine?
Why is it blocking when running from the vzdump machinery?