linux-ext4 - Re: [PATCH 2/3] ext4: use ext4_write_inode() when fsyncing w/o a journal

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Date:   Wed, 23 Jan 2019 12:34:55 +0100
From:   Jan Kara <jack@...e.cz>
To:     Theodore Ts'o <tytso@....edu>
Cc:     Ext4 Developers List <linux-ext4@...r.kernel.org>,
        stable@...nel.org
Subject: Re: [PATCH 2/3] ext4: use ext4_write_inode() when fsyncing w/o a
 journal

On Mon 31-12-18 14:48:35, Theodore Ts'o wrote:
> In no-journal mode, we previously used __generic_file_fsync() in
> no-journal mode.  This triggers a lockdep warning, and in addition,
> it's not safe to depend on the inode writeback mechanism in the case
> ext4.  We can solve both problems by calling ext4_write_inode()
> directly.
> 
> Signed-off-by: Theodore Ts'o <tytso@....edu>
> Cc: stable@...nel.org
> ---
>  fs/ext4/fsync.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/ext4/fsync.c b/fs/ext4/fsync.c
> index 26a7fe5c4fd3..87a7ff00ef62 100644
> --- a/fs/ext4/fsync.c
> +++ b/fs/ext4/fsync.c
> @@ -116,8 +116,16 @@ int ext4_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
>  		goto out;
>  	}
>  
> +	ret = file_write_and_wait_range(file, start, end);
> +	if (ret)
> +		return ret;
> +
>  	if (!journal) {
> -		ret = __generic_file_fsync(file, start, end, datasync);
> +		struct writeback_control wbc = {
> +			.sync_mode = WB_SYNC_ALL
> +		};
> +
> +		ret = ext4_write_inode(inode, &wbc);

Going through some older email... How come this is safe Ted?
ext4_write_inode() will not write out metadata buffers associated with the
inode (unlike __generic_file_fsync() which calls sync_mapping_buffers()).
So you probably need to call sync_mapping_buffers() before calling
ext4_write_inode() here?

								Honza

> @@ -125,9 +133,6 @@ int ext4_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
>  		goto out;
>  	}
>  
> -	ret = file_write_and_wait_range(file, start, end);
> -	if (ret)
> -		return ret;
>  	/*
>  	 * data=writeback,ordered:
>  	 *  The caller's filemap_fdatawrite()/wait will sync the data.
> -- 
> 2.19.1
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR