5.11 free space tree remount warning

5.11 free space tree remount warning

[Chris Murphy]

Hi,

systemd does remount ro at reboot/shutdown time, and if free space
tree exists, this is always logged:

[   27.476941] systemd-shutdown[1]: Unmounting file systems.
[   27.479756] [1601]: Remounting '/' read-only in with options
'seclabel,compress=zstd:1,space_cache=v2,subvolid=258,subvol=/root'.
[   27.489196] BTRFS info (device vda3): using free space tree
[   27.492009] BTRFS warning (device vda3): remount supports changing
free space tree only from ro to rw

Is there a way to better detect that this isn't an attempt to change
to v2? If there's no v1 present, it's not a change.

-- 
Chris Murphy

Re: 5.11 free space tree remount warning

[Wang Yugui]

Hi, Boris Burkov, Chris Murphy

This happened is my server too.

1, this warning [*1] is not loged in /var/log/messages
    because it happened after the ro remount of /
   my server is a dell PowerEdge T640, this log can be confirmed by
iDRAC console.

[*1]  BTRFS warning (device vda3): remount supports changing free space
tree only from ro to rw

2, no space_cache=v2 in /etc/fstab
   but space_cache=v2 is reported in /proc/mounts
   systemd-shutdown ro remount / with the param based on /proc/mount

Best Regards
Wang Yugui (wangyugui@e16-tech.com)
2021/02/21

> Hi,
> 
> systemd does remount ro at reboot/shutdown time, and if free space
> tree exists, this is always logged:
> 
> [   27.476941] systemd-shutdown[1]: Unmounting file systems.
> [   27.479756] [1601]: Remounting '/' read-only in with options
> 'seclabel,compress=zstd:1,space_cache=v2,subvolid=258,subvol=/root'.
> [   27.489196] BTRFS info (device vda3): using free space tree
> [   27.492009] BTRFS warning (device vda3): remount supports changing
> free space tree only from ro to rw
> 
> Is there a way to better detect that this isn't an attempt to change
> to v2? If there's no v1 present, it's not a change.
> 
> -- 
> Chris Murphy

Re: 5.11 free space tree remount warning

[Chris Murphy]

On Sat, Feb 20, 2021 at 5:26 PM Wang Yugui <wangyugui@e16-tech.com> wrote:

> 1, this warning [*1] is not loged in /var/log/messages
>     because it happened after the ro remount of /
>    my server is a dell PowerEdge T640, this log can be confirmed by
> iDRAC console.

This is a fair point. The systemd journal is also not logging this for
the same reason. I see it on the console on reboots when there's
enough of a delay to notice it, and "warning" pretty much always
catches my eye.


-- 
Chris Murphy

Re: 5.11 free space tree remount warning

[Boris Burkov]

On Fri, Feb 19, 2021 at 07:01:41PM -0700, Chris Murphy wrote:
> Hi,
> 
> systemd does remount ro at reboot/shutdown time, and if free space
> tree exists, this is always logged:
> 
> [   27.476941] systemd-shutdown[1]: Unmounting file systems.
> [   27.479756] [1601]: Remounting '/' read-only in with options
> 'seclabel,compress=zstd:1,space_cache=v2,subvolid=258,subvol=/root'.
> [   27.489196] BTRFS info (device vda3): using free space tree
> [   27.492009] BTRFS warning (device vda3): remount supports changing
> free space tree only from ro to rw
> 
> Is there a way to better detect that this isn't an attempt to change
> to v2? If there's no v1 present, it's not a change.
> 
> -- 
> Chris Murphy

I am able to reproduce this with:

mkfs.btrfs -f dev
mount -o space_cache=v2 dev mnt
mount -o remount,ro mnt

At first I assumed I just completely ignored this case, but reading the
code now, it looks like it should have handled it. I assume I messed
up the value of the mount option during a remount when it isn't set by
the mount command.

Apologies for the noise, and I should hopefully have a fix soon.
Boris