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Date:   Mon, 19 Jul 2021 18:15:56 -0700
From:   Jaegeuk Kim <jaegeuk@kernel.org>
To:     Chao Yu <chao@kernel.org>
Cc:     linux-f2fs-devel@lists.sourceforge.net,
        linux-kernel@vger.kernel.org, Chao Yu <chao.yu@linux.dev>
Subject: Re: [PATCH v3] f2fs: fix to force keeping write barrier for strict
 fsync mode
Message-ID: <YPYjzAVq04LfUO2Y@google.com>
References: <20210720010329.3975-1-chao@kernel.org>
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Wasn't it supposed to be v1?

On 07/20, Chao Yu wrote:
> [1] https://www.mail-archive.com/linux-f2fs-devel@lists.sourceforge.net/msg15126.html
> 
> As [1] reported, if lower device doesn't support write barrier, in below
> case:
> 
> - write page #0; persist
> - overwrite page #0
> - fsync
>  - write data page #0 OPU into device's cache
>  - write inode page into device's cache
>  - issue flush
> 
> If SPO is triggered during flush command, inode page can be persisted
> before data page #0, so that after recovery, inode page can be recovered
> with new physical block address of data page #0, however there may
> contains dummy data in new physical block address.
> 
> Then what user will see is: after overwrite & fsync + SPO, old data in
> file was corrupted, if any user do care about such case, we can suggest
> user to use STRICT fsync mode, in this mode, we will force to use atomic
> write sematics to keep write order in between data/node and last node,
> so that it avoids potential data corruption during fsync().
> 
> Signed-off-by: Chao Yu <chao@kernel.org>
> ---
>  fs/f2fs/file.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> index 6afd4562335f..00b45876eaa1 100644
> --- a/fs/f2fs/file.c
> +++ b/fs/f2fs/file.c
> @@ -301,6 +301,18 @@ static int f2fs_do_sync_file(struct file *file, loff_t start, loff_t end,
>  				f2fs_exist_written_data(sbi, ino, UPDATE_INO))
>  			goto flush_out;
>  		goto out;
> +	} else {
> +		/*
> +		 * for OPU case, during fsync(), node can be persisted before
> +		 * data when lower device doesn't support write barrier, result
> +		 * in data corruption after SPO.
> +		 * So for strict fsync mode, force to use atomic write sematics
> +		 * to keep write order in between data/node and last node to
> +		 * avoid potential data corruption.
> +		 */
> +		if (F2FS_OPTION(sbi).fsync_mode ==
> +				FSYNC_MODE_STRICT && !atomic)
> +			atomic = true;
>  	}
>  go_write:
>  	/*
> -- 
> 2.22.1