linux-kernel - Re: [PATCH v4] F2FS: invalidate META

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Date:   Tue, 2 Nov 2021 15:36:07 +0800
From:   Chao Yu <chao@...nel.org>
To:     Hyeong-Jun Kim <hj514.kim@...sung.com>,
        Jaegeuk Kim <jaegeuk@...nel.org>
Cc:     linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] F2FS: invalidate META_MAPPING before IPU/DIO write

On 2021/11/2 15:10, 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@...sung.com>

Reviewed-by: Chao Yu <chao@...nel.org>

Thanks,