Re: [PATCH v2] F2FS: invalidate META_MAPPING before IPU/DIO write

From: Chao Yu
Date: Mon Nov 01 2021 - 21:29:01 EST


On 2021/11/1 16:46, Hyeong-Jun Kim wrote:
Encrypted pages during GC are read and cached in META_MAPPING.
However, due to cached pages in META_MAPPING, there is an issue where
newly written pages are lost by IPU or DIO writes.

Thread A - f2fs_gc() Thread B
/* phase 3 */
down_write(i_gc_rwsem)
ra_data_block() ---- (a)
up_write(i_gc_rwsem)
f2fs_direct_IO() :
- down_read(i_gc_rwsem)
- __blockdev_direct_io()
- get_data_block_dio_write()
- f2fs_dio_submit_bio() ---- (b)
- up_read(i_gc_rwsem)
/* phase 4 */
down_write(i_gc_rwsem)
move_data_block() ---- (c)
up_write(i_gc_rwsem)

(a) In phase 3 of f2fs_gc(), up-to-date page is read from storage and
cached in META_MAPPING.
(b) In thread B, writing new data by IPU or DIO write on same blkaddr as
read in (a). cached page in META_MAPPING become out-dated.
(c) In phase 4 of f2fs_gc(), out-dated page in META_MAPPING is copied to
new blkaddr. In conclusion, the newly written data in (b) is lost.

To address this issue, invalidating pages in META_MAPPING before IPU or
DIO write.

Fixes: 6aa58d8ad20a ("f2fs: readahead encrypted block during GC")
Signed-off-by: Hyeong-Jun Kim <hj514.kim@xxxxxxxxxxx>

Reviewed-by: Chao Yu <chao@xxxxxxxxxx>

Thanks,