btrfs: qgroup: Fix wrong qgroup reservation update for relationship modification
When modifying qgroup relationship, for qgroup which only owns exclusive extents, we will go through quick update path. In this path, we will add/subtract exclusive and reference number for parent qgroup, since the source (child) qgroup only has exclusive extents, destination (parent) qgroup will also own or lose those extents exclusively. The same should be the same for reservation, since later reservation adding/releasing will also affect parent qgroup, without the reservation carried from child, parent will underflow reservation or have dead reservation which will never be freed. However original code doesn't do the same thing for reservation. It handles qgroup reservation quite differently: It removes qgroup reservation, as it's allocating space from the reserved qgroup for relationship adding. But does nothing for qgroup reservation if we're removing a qgroup relationship. According to the original code, it looks just like because we're adding qgroup->rfer, the code assumes we're writing new data, so it's follows the normal write routine, by reducing qgroup->reserved and adding qgroup->rfer/excl. This old behavior is wrong, and should be fixed to follow the same excl/rfer behavior. Just fix it by using the correct behavior described above. Fixes: 31193213 ("Btrfs: qgroup: Introduce a may_use to account space_info->bytes_may_use.") Signed-off-by: NQu Wenruo <wqu@suse.com> Signed-off-by: NDavid Sterba <dsterba@suse.com>
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