Re: [PATCH v2 0/2] btrfs: qgroup rescan fixes part 1

[David Sterba <dsterba@suse.cz>]

On Mon, May 14, 2018 at 09:38:11AM +0800, Qu Wenruo wrote:
> This patchset is mainly focused on fixing qgroup rescan corruption.
> 
> Since the whole btrfs qgroup is based on the modification between 2
> transactions, it only has correct qgroup delta.
> While if the rescan can't provide a correct result from the very
> beginning, qgroup numbers are corrupted.
> 
> The patchset is fixing two types of qgroup corruption which could happen
> by looping btrfs/017 with some possibility.
> 
> 1) Not accounting tree blocks
>    Caused by the fact that qgroup rescan only searches commit root for
>    backref, while we're passing current extent root to search.
>    Fix it by also passing commit extent root.
> 
> 2) Double accounting tree blocks
>    Caused by wrong rescan exit condition.
>    Currently qgroup only exit when it can't find any leaves beyond
>    rescan progress.
>    However it could cause problem when new transaction happens after
>    last rescan, and old leaves CoWed to new location, and double
>    accounting could happen.
>    Fix it by checking and leave qgroup rescan if we have hit last leaf,
>    instead of leaving it to next leaf rescan.
> 
> 
> Changelog:
> v2:
>   Remove unused tree_mod_seq_elem for the 1st patch.
>   Fix double unlock in 2nd patch.
>   Thanks Jeff for the update.

V1 patches replaced, thanks.