Re: [PATCH] f2fs: force out-place update for all writes on compressed file

[Chao Yu]

On 9/7/26 19:35, Jiucheng Xu via B4 Relay wrote:
> From: Jiucheng Xu <jiucheng.xu@xxxxxxxxxxx>
>
> For compressed file, compressed write may fail and fall back to raw
> write.
>
> -Thread A                                         - Thread B
>    - f2fs_write_multi_pages                          - f2fs_down_write(&sbi->cp_rwsem);
>     - f2fs_write_compressed_pages                    - ...
>      - f2fs_trylock_op                               - ...
>       - f2fs_down_read_trylock(&sbi->cp_rwsem);      - ...
>     - f2fs_write_raw_pages                           - ...
>
> Thread B acquires the lock first, which causes Thread A to fail lock
> acquisition and fall back to raw-data write.
> IPU_FORCE is enabled on small-capacity storage devices (< 16GB),
> so f2fs_write_raw_pages() overwrites the original compressed data
> in-place.
>
> The in-memory node has been updated with raw-data addresses, while the
> node metadata stored on eMMC still remains in compressed state.
> If a power-cut occurs before the node is flushed to disk, on-disk
> inconsistency arises: disk data is raw, yet metadata treats it as a
> compressed cluster, leading to decompression failure.
>
> To eliminate this risk completely, force out-place update for all
> write operations on compressed file.

Cc: stable@xxxxxxxxxx
Fixes: 4c8ff7095bef ("f2fs: support data compression")

> Signed-off-by: Jiucheng Xu <jiucheng.xu@xxxxxxxxxxx>

Reviewed-by: Chao Yu <chao@xxxxxxxxxx>

Thanks,