Hi, the following patches try to fix a long outstanding issue with qgroups
and snapshot deletion. The core problem is that btrfs_drop_snapshot will
skip shared extents during it's tree walk. This results in an inconsistent
qgroup state once the drop is processed. We also have a bug where qgroup
items are not deleted after drop_snapshot. The orphaned items will cause
btrfs to go readonly when a snapshot is created with the same id as the
deleted one.
The first patch adds some tracing which I found very useful in debugging
qgroup operations. The second patch is an actual fix to the problem. A third
patch, from Josef is also added. We need this because it fixes at least one
set of inconsistencies qgroups can get to via drop_snapshot. The fourth
patch adds code to delete qgroup items from disk once drop_snapshot has
completed.
With this version of the patch series, I can no longer reproduce
qgroup inconsistencies via drop_snapshot on my test disks.
Change from last patch set:
- Added patch 'btrfs: delete qgroup items in drop_snapshot'
Changes from V2-V3:
- search on bytenr and root, but not seq in btrfs_record_ref when
we're looking for existing qgroup operations.
Changes before that (V1-V2):
- remove extra extent_buffer_uptodate call from account_shared_subtree()
- catch return values for the accounting calls now and do the right thing
(log an error and tell the user to rescan)
- remove the loop on roots in qgroup_subtree_accounting and just use the
nnodes member to make our first decision.
- Don't queue up the subtree root for a change (the code in drop_snapshot
handkles qgroup updates for this block).
- only walk subtrees if we're actually in DROP_REFERENCE stage and we're
going to call free_extent
- account leaf items for level zero blocks that we are dropping in
walk_up_proc
Please review, thanks. Diffstat follows,
--Mark
fs/btrfs/ctree.c | 20 +-
fs/btrfs/ctree.h | 4
fs/btrfs/extent-tree.c | 291 +++++++++++++++++++++++++++++++++++++++++--
fs/btrfs/qgroup.c | 282 +++++++++++++++++++++++++++++++++++++++++
fs/btrfs/qgroup.h | 4
fs/btrfs/super.c | 1
include/trace/events/btrfs.h | 57 ++++++++
7 files changed, 631 insertions(+), 28 deletions(-)
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