Commits
Qu Wenruo committed a12b877b557
btrfs: qgroup: Fix qgroup reserved space underflow caused by buffered write and quotas being enabled
[BUG]
Under the following case, we can underflow qgroup reserved space.
Task A | Task B
---------------------------------------------------------------
Quota disabled |
Buffered write |
|- btrfs_check_data_free_space() |
| *NO* qgroup space is reserved |
| since quota is *DISABLED* |
|- All pages are copied to page |
cache |
| Enable quota
| Quota scan finished
|
| Sync_fs
| |- run_delalloc_range
| |- Write pages
| |- btrfs_finish_ordered_io
| |- insert_reserved_file_extent
| |- btrfs_qgroup_release_data()
| Since no qgroup space is
reserved in Task A, we
underflow qgroup reserved
space
This can be detected by fstest btrfs/104.
[CAUSE]
In insert_reserved_file_extent() we tell qgroup to release the @ram_bytes
size of qgroup reserved_space in all cases.
And btrfs_qgroup_release_data() will check if quotas are enabled.
However in the above case, the buffered write happens before quota is
enabled, so we don't have the reserved space for that range.
[FIX]
In insert_reserved_file_extent(), we tell qgroup to release the acctual
byte number it released.
In the above case, since we don't have the reserved space, we tell
qgroups to release 0 byte, so the problem can be fixed.
And thanks to the @reserved parameter introduced by the qgroup rework,
and previous patch to return released bytes, the fix can be as small as
10 lines.
Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
[ changelog updates ]
Signed-off-by: David Sterba <dsterba@suse.com>