filesystems mounted within a newly created bind mount tree are not accessible until remount on host

[fiveangle]

I've found what appears to be a bug on PVE 6.4. I am running 5.11 kernel but have not tested on 5.4 kernel.

Linux richie 5.11.17-1-pve #1 SMP PVE 5.11.17-1~bpo10 (Wed, 12 May 2021 12:45:37 +0200) x86_64 GNU/Linux

Containers that have a configured bind mount point will restore correctly, but any mounted file systems that exist within the bind mount tree are inaccessible until remounted on the host.

Example:

File systems are mounted on the host at /farm:

root@richie:/farm# mount|grep transfer7
/dev/sde1 on /farm/transfer7 type exfat (rw,relatime,fmask=0022,dmask=0022,iocharset=utf8,errors=remount-ro)

LXC container has bind mount for /farm to host /farm then is backed up and restored with "Unpriveledged" set to "No", and then started:

root@richie:/farm# pct list|egrep 'VMID|102'
VMID       Status     Lock         Name
102        running                 chiapet

Confirm restored container contains bind mount of /farm to hosts /farm:

root@richie:/farm# pct df 102
MP     Volume                   Size  Used Avail Use% Path
rootfs local-lvm:vm-102-disk-0 62.5G 27.6G 31.7G  0.4 /
mp0    /farm                   54.6G 46.0G  5.8G  0.8 /farm

Observe contents of mounted file systems inaccessible from within container but is accessble from host:

On container:
root@chiapet:/farm# ls transfer7/*
ls: cannot access 'transfer7/*': No such file or directory

On host:
root@richie:/farm# ls -l transfer7/
total 512
drwxr-xr-x 2 root root 131072 May 24 16:10  plots
-rwxr-xr-x 1 root root      5 May 22 13:48  sata
drwxr-xr-x 2 root root 131072 May 26 04:19 'System Volume Information'
-rwxr-xr-x 1 root root     10 May 22 13:48  transfer7

Remount file system with identical mount method as before restore of container:

root@richie:/farm# umount /farm/transfer7
root@richie:/farm# mount /dev/disk/by-label/transfer7 /farm/transfer7/
root@richie:/farm# mount|grep transfer7
/dev/sde1 on /farm/transfer7 type exfat (rw,relatime,fmask=0022,dmask=0022,iocharset=utf8,errors=remount-ro)

Observe contents of mounted file system in bind mount tree is now accessible within the container

root@chiapet:/farm# ls -l transfer7/
total 512
drwxr-xr-x 2 root root 131072 May 26 04:19 'System Volume Information'
drwxr-xr-x 2 root root 131072 May 24 16:10  plots
-rwxr-xr-x 1 root root      5 May 22 13:48  sata
-rwxr-xr-x 1 root root     10 May 22 13:48  transfer7

Is this working as designed, and if so, why ? And if not, how best to communicate to the dev team ?

Thanks !

 

[fiveangle]

New information: if you restart the LXC, the mounted file systems are once again inaccessible. Umount/mount once again restores access but "mount -o remount <mount path>" does not.

Can anyone confirm this does not occur with 5.4 kernel ? I will have to forego wireguard functionality if I downgrade, but this bug is more of a problem, and I can move wireguard to virtual machine if necessary.

Thanks !

 

[fiveangle]

https://bugzilla.proxmox.com/show_bug.cgi?id=3493