linux-kernel - Re: [PATCH] f2fs: fix to force keeping write barrier for strict fsync mode

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Message-ID: <20200123221855.GA7917@jaegeuk-macbookpro.roam.corp.google.com>
Date:   Thu, 23 Jan 2020 14:18:55 -0800
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Chao Yu <yuchao0@...wei.com>
Cc:     linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, chao@...nel.org
Subject: Re: [PATCH] f2fs: fix to force keeping write barrier for strict
 fsync mode

On 01/20, Chao Yu wrote:
> If barrier is enabled, for strict fsync mode, we should force to
> use atomic write semantics to avoid data corruption due to no
> barrier support in lower device.
> 
> Signed-off-by: Chao Yu <yuchao0@...wei.com>
> ---
>  fs/f2fs/file.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> index 86ddbb55d2b1..c9dd45f82fbd 100644
> --- a/fs/f2fs/file.c
> +++ b/fs/f2fs/file.c
> @@ -241,6 +241,13 @@ static int f2fs_do_sync_file(struct file *file, loff_t start, loff_t end,
>  	};
>  	unsigned int seq_id = 0;
>  
> +	/*
> +	 * for strict fsync mode, force to keep atomic write sematics to avoid
> +	 * data corruption if lower device doesn't support write barrier.
> +	 */
> +	if (!atomic && F2FS_OPTION(sbi).fsync_mode == FSYNC_MODE_STRICT)
> +		atomic = true;

This allows to relax IO ordering and cache flush. I'm not sure that's what you
want to do here for strict mode.

> +
>  	if (unlikely(f2fs_readonly(inode->i_sb) ||
>  				is_sbi_flag_set(sbi, SBI_CP_DISABLED)))
>  		return 0;
> -- 
> 2.18.0.rc1