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

[Chao Yu]

On 2021/11/1 13:42, 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                              Thread B
> - f2fs_gc(): blk 0x10 -> 0x20 (a)
>                                        - IPU or DIO write on blk 0x20 (b)
> - f2fs_gc(): blk 0x20 -> 0x30 (c)
>
> (a) page for blk 0x20 is cached in META_MAPPING and page for blk 0x10
>      is invalidated from META_MAPPING.
> (b) write new data to blk 0x200 using IPU or DIO, but outdated data
>      still remains in META_MAPPING.
> (c) f2fs_gc() try to move blk from 0x20 to 0x30 using cached page in
>      META_MAPPING. In conclusion, the newly written data in (b) is lost.

In c), f2fs_gc() will readahead encrypted block from disk via ra_data_block() anyway,
not matter cached encrypted page of meta inode is uptodate or not, so it's safe, right?

Am I missing anything?

Thanks,

> To address this issue, invalidating pages in META_MAPPING before IPU or
> DIO write.
>
> Signed-off-by: Hyeong-Jun Kim <hj514.kim@xxxxxxxxxxx>
> ---
>   fs/f2fs/data.c    | 2 ++
>   fs/f2fs/segment.c | 3 +++
>   2 files changed, 5 insertions(+)
>
> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> index 74e1a350c1d8..9f754aaef558 100644
> --- a/fs/f2fs/data.c
> +++ b/fs/f2fs/data.c
> @@ -1708,6 +1708,8 @@ int f2fs_map_blocks(struct inode *inode, struct f2fs_map_blocks *map,
>   		 */
>   		f2fs_wait_on_block_writeback_range(inode,
>   						map->m_pblk, map->m_len);
> +		invalidate_mapping_pages(META_MAPPING(sbi),
> +						map->m_pblk, map->m_pblk);
>   
>   		if (map->m_multidev_dio) {
>   			block_t blk_addr = map->m_pblk;
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index 526423fe84ce..f57c55190f9e 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -3652,6 +3652,9 @@ int f2fs_inplace_write_data(struct f2fs_io_info *fio)
>   		goto drop_bio;
>   	}
>   
> +	invalidate_mapping_pages(META_MAPPING(fio->sbi),
> +				fio->new_blkaddr, fio->new_blkaddr);
> +
>   	stat_inc_inplace_blocks(fio->sbi);
>   
>   	if (fio->bio && !(SM_I(sbi)->ipu_policy & (1 << F2FS_IPU_NOCACHE)))