From: Qu Wenruo wqu@suse.com
[ Upstream commit cbab8ade585a18c4334b085564d9d046e01a3f70 ]
[BUG] For the following operation, qgroup is guaranteed to be screwed up due to snapshot adding to a new qgroup:
# mkfs.btrfs -f $dev # mount $dev $mnt # btrfs qgroup en $mnt # btrfs subv create $mnt/src # xfs_io -f -c "pwrite 0 1m" $mnt/src/file # sync # btrfs qgroup create 1/0 $mnt/src # btrfs subv snapshot -i 1/0 $mnt/src $mnt/snapshot # btrfs qgroup show -prce $mnt/src qgroupid rfer excl max_rfer max_excl parent child -------- ---- ---- -------- -------- ------ ----- 0/5 16.00KiB 16.00KiB none none --- --- 0/257 1.02MiB 16.00KiB none none --- --- 0/258 1.02MiB 16.00KiB none none 1/0 --- 1/0 0.00B 0.00B none none --- 0/258 ^^^^^^^^^^^^^^^^^^^^
[CAUSE] The problem is in btrfs_qgroup_inherit(), we don't have good enough check to determine if the new relation would break the existing accounting.
Unlike btrfs_add_qgroup_relation(), which has proper check to determine if we can do quick update without a rescan, in btrfs_qgroup_inherit() we can even assign a snapshot to multiple qgroups.
[FIX] Fix it by manually marking qgroup inconsistent for snapshot inheritance.
For subvolume creation, since all its extents are exclusively owned, we don't need to rescan.
In theory, we should call relation check like quick_update_accounting() when doing qgroup inheritance and inform user about qgroup accounting inconsistency.
But we don't have good mechanism to relay that back to the user in the snapshot creation context, thus we can only silently mark the qgroup inconsistent.
Anyway, user shouldn't use qgroup inheritance during snapshot creation, and should add qgroup relationship after snapshot creation by 'btrfs qgroup assign', which has a much better UI to inform user about qgroup inconsistent and kick in rescan automatically.
Reviewed-by: Josef Bacik josef@toxicpanda.com Signed-off-by: Qu Wenruo wqu@suse.com Reviewed-by: David Sterba dsterba@suse.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Sasha Levin sashal@kernel.org --- fs/btrfs/qgroup.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+)
diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c index 590defdf8860..b94f6f99e90d 100644 --- a/fs/btrfs/qgroup.c +++ b/fs/btrfs/qgroup.c @@ -2636,6 +2636,7 @@ int btrfs_qgroup_inherit(struct btrfs_trans_handle *trans, u64 srcid, struct btrfs_root *quota_root; struct btrfs_qgroup *srcgroup; struct btrfs_qgroup *dstgroup; + bool need_rescan = false; u32 level_size = 0; u64 nums;
@@ -2779,6 +2780,13 @@ int btrfs_qgroup_inherit(struct btrfs_trans_handle *trans, u64 srcid, goto unlock; } ++i_qgroups; + + /* + * If we're doing a snapshot, and adding the snapshot to a new + * qgroup, the numbers are guaranteed to be incorrect. + */ + if (srcid) + need_rescan = true; }
for (i = 0; i < inherit->num_ref_copies; ++i, i_qgroups += 2) { @@ -2798,6 +2806,9 @@ int btrfs_qgroup_inherit(struct btrfs_trans_handle *trans, u64 srcid,
dst->rfer = src->rfer - level_size; dst->rfer_cmpr = src->rfer_cmpr - level_size; + + /* Manually tweaking numbers certainly needs a rescan */ + need_rescan = true; } for (i = 0; i < inherit->num_excl_copies; ++i, i_qgroups += 2) { struct btrfs_qgroup *src; @@ -2816,6 +2827,7 @@ int btrfs_qgroup_inherit(struct btrfs_trans_handle *trans, u64 srcid,
dst->excl = src->excl + level_size; dst->excl_cmpr = src->excl_cmpr + level_size; + need_rescan = true; }
unlock: @@ -2823,6 +2835,8 @@ unlock: out: if (!committing) mutex_unlock(&fs_info->qgroup_ioctl_lock); + if (need_rescan) + fs_info->qgroup_flags |= BTRFS_QGROUP_STATUS_FLAG_INCONSISTENT; return ret; }