linux-ext4 - Re: [PATCH] ext4: Properly sync file size update after O

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Message-ID: <ZSc9J9zFChyxl1U2@dread.disaster.area>
Date:   Thu, 12 Oct 2023 11:26:15 +1100
From:   Dave Chinner <david@...morbit.com>
To:     Jan Kara <jack@...e.cz>
Cc:     Ted Tso <tytso@....edu>, linux-ext4@...r.kernel.org,
        "Ritesh Harjani (IBM)" <ritesh.list@...il.com>,
        Gao Xiang <hsiangkao@...ux.alibaba.com>
Subject: Re: [PATCH] ext4: Properly sync file size update after O_SYNC direct
 IO

On Wed, Oct 11, 2023 at 04:21:55PM +0200, Jan Kara wrote:
> Gao Xiang has reported that on ext4 O_SYNC direct IO does not properly
> sync file size update and thus if we crash at unfortunate moment, the
> file can have smaller size although O_SYNC IO has reported successful
> completion. The problem happens because update of on-disk inode size is
> handled in ext4_dio_write_iter() *after* iomap_dio_rw() (and thus
> dio_complete() in particular) has returned and generic_file_sync() gets
> called by dio_complete(). Fix the problem by handling on-disk inode size
> update directly in our ->end_io completion handler.
> 
> References: https://lore.kernel.org/all/02d18236-26ef-09b0-90ad-030c4fe3ee20@linux.alibaba.com
> Reported-by: Gao Xiang <hsiangkao@...ux.alibaba.com>
> Signed-off-by: Jan Kara <jack@...e.cz>
> ---
>  fs/ext4/file.c | 139 ++++++++++++++++++-------------------------------
>  1 file changed, 52 insertions(+), 87 deletions(-)
.....
> @@ -388,9 +342,28 @@ static ssize_t ext4_handle_inode_extension(struct inode *inode, loff_t offset,
>  		 */
>  		if (inode->i_nlink)
>  			ext4_orphan_del(NULL, inode);
> +		return;
>  	}
> +	/*
> +	 * If i_disksize got extended due to writeback of delalloc blocks while
> +	 * the DIO was running we could fail to cleanup the orphan list in
> +	 * ext4_handle_inode_extension(). Do it now.
> +	 */
> +	if (!list_empty(&EXT4_I(inode)->i_orphan) && inode->i_nlink) {
> +		handle_t *handle = ext4_journal_start(inode, EXT4_HT_INODE, 2);

So this has to be called after the DIO write completes and calls
ext4_handle_inode_extension()?

....

> @@ -606,9 +570,8 @@ static ssize_t ext4_dio_write_iter(struct kiocb *iocb, struct iov_iter *from)
>  			   dio_flags, NULL, 0);
>  	if (ret == -ENOTBLK)
>  		ret = 0;
> -
>  	if (extend)
> -		ret = ext4_handle_inode_extension(inode, offset, ret, count);
> +		ext4_inode_extension_cleanup(inode, ret);

Because this doesn't wait for AIO DIO to complete and actually
extend the file before running the cleanup code...

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com