On Mon, Jun 28, 2021 at 05:57:28PM +0900, Naohiro Aota wrote:
> Damien reported a test failure with btrfs/209. The test itself ran fine,
> but the fsck run afterwards reported a corrupted filesystem.
>
> The filesystem corruption happens because we're splitting an extent and
> then writing the extent twice. We have to split the extent though, because
> we're creating too large extents for a REQ_OP_ZONE_APPEND operation.
>
> When dumping the extent tree, we can see two EXTENT_ITEMs at the same
> start address but different lengths.
>
> $ btrfs inspect dump-tree /dev/nullb1 -t extent
> ...
> item 19 key (269484032 EXTENT_ITEM 126976) itemoff 15470 itemsize 53
> refs 1 gen 7 flags DATA
> extent data backref root FS_TREE objectid 257 offset 786432 count 1
> item 20 key (269484032 EXTENT_ITEM 262144) itemoff 15417 itemsize 53
> refs 1 gen 7 flags DATA
> extent data backref root FS_TREE objectid 257 offset 786432 count 1
>
> The duplicated EXTENT_ITEMs originally come from wrongly split extent_map in
> extract_ordered_extent(). Since extract_ordered_extent() uses
> create_io_em() to split an existing extent_map, we will have
> split->orig_start != split->start. Then, it will be logged with non-zero
> "extent data offset". Finally, the logged entries are replayed into
> a duplicated EXTENT_ITEM.
>
> Introduce and use proper splitting function for extent_map. The function is
> intended to be simple and specific usage for extract_ordered_extent() e.g.
> not supporting compression case (we do not allow splitting compressed
> extent_map anyway).
>
> Fixes: d22002fd37bd ("btrfs: zoned: split ordered extent when bio is sent")
> Cc: stable@xxxxxxxxxxxxxxx # 5.12+
> Reported-by: Damien Le Moal <damien.lemoal@xxxxxxx>
> Cc: Johannes Thumshirn <johannes.thumshirn@xxxxxxx>
> Signed-off-by: Naohiro Aota <naohiro.aota@xxxxxxx>
Added to a topic branch, I think I've hit the problem this patch is
supposed to fix so I'll to reproduce it before adding it to misc-next.
I've added Daminen's answer to the changelog as it's really helpful to
understand why it's fixed that way.
