Re: [PATCH] btrfs-progs: do not allow setting seed flag on fs with dirty log

[Josef Bacik <josef@toxicpanda.com>]

On Fri, Apr 15, 2022 at 07:37:43PM +0800, Qu Wenruo wrote:
> [BUG]
> The following sequence operation can lead to a seed fs rejected by
> kernel:
> 
>  # Generate a fs with dirty log
>  mkfs.btrfs -f $file
>  mount $dev $mnt
>  xfs_io -f -c "pwrite 0 16k" -c fsync $mnt/file
>  cp $file $file.backup
>  umount $mnt
>  mv $file.backup $file
> 
>  # now $file has dirty log, set seed flag on it
>  btrfstune -S1 $file
> 
>  # mount will fail
>  mount $file $mnt
> 
> The mount failure with the following dmesg:
> 
> [  980.363667] loop0: detected capacity change from 0 to 262144
> [  980.371177] BTRFS info (device loop0): flagging fs with big metadata feature
> [  980.372229] BTRFS info (device loop0): using free space tree
> [  980.372639] BTRFS info (device loop0): has skinny extents
> [  980.375075] BTRFS info (device loop0): start tree-log replay
> [  980.375513] BTRFS warning (device loop0): log replay required on RO media
> [  980.381652] BTRFS error (device loop0): open_ctree failed
> 
> [CAUSE]
> Although btrfs will replay its dirty log even with RO mount, but kernel
> will treat seed device as RO device, and dirty log can not be replayed
> on RO device.
> 
> This rejection is already the better end, just imagine if we don't treat
> seed device as RO, and replayed the dirty log.
> The filesystem relying on the seed device will be completely screwed up.
> 
> [FIX]
> Just add extra check on log tree in btrfstune to reject setting seed
> flag on filesystems with dirty log.
> 
> Signed-off-by: Qu Wenruo <wqu@suse.com>

Can we get a progs test for this as well?

Reviewed-by: Josef Bacik <josef@toxicpanda.com>

Thanks,

Josef