linux-ext4 - Re: [PATCH 2/2] ext4: dax: keep orphan list before truncate overflow allocated blocks

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Message-ID: <20240827170813.twxnsgkqp2vraavz@quack3>
Date: Tue, 27 Aug 2024 19:08:13 +0200
From: Jan Kara <jack@...e.cz>
To: yangerkun <yangerkun@...weicloud.com>
Cc: tytso@....edu, adilger.kernel@...ger.ca, jack@...e.cz,
	linux-ext4@...r.kernel.org, yangerkun@...wei.com,
	chengzhihao1@...wei.com
Subject: Re: [PATCH 2/2] ext4: dax: keep orphan list before truncate overflow
 allocated blocks

On Tue 20-08-24 22:06:57, yangerkun wrote:
> From: yangerkun <yangerkun@...wei.com>

Thanks for debugging this. Couple of spelling fixes first:
 
> Any extended write for ext4 requires the inode to be placed on the
      ^^^ extending

> orphan list before the actual write. In addition, the inode can be
> actually removed from the orphan list only after all writes are
> completed. Otherwise, those overcommitted blocks (If the allocated
	     ^^ I'd phrase this: Otherwise we'd leave allocated blocks
beyond i_disksize if we could not copy all the data into allocated block
and e2fsck would complain.

> blocks are not written due to certain reasons, the inode size does not
> exceed the offset of these blocks) The leak status is always retained,
> and fsck reports an alarm for this scenario.
> 
> Currently, the dio and buffer IO comply with this logic. However, the
			 ^^ buffered

BTW: The only reason why direct IO doesn't have this problem is because
we don't do short writes for direct IO. We either submit all or we return
error.

> dax write will removed the inode from orphan list since
		  ^^^ remove           ^ the orphan ...

> ext4_handle_inode_extension is unconditionally called during extend
								^^ extending

> write. Fix it with this patch. We open the code from
> ext4_handle_inode_extension since we want to keep the blocks valid
> has been allocated and write success.
> 
> Signed-off-by: yangerkun <yangerkun@...wei.com>
> ---
>  fs/ext4/file.c | 35 +++++++++++++++++++++++++++++++----
>  1 file changed, 31 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/ext4/file.c b/fs/ext4/file.c
> index be061bb64067..fd8597eef75e 100644
> --- a/fs/ext4/file.c
> +++ b/fs/ext4/file.c
> @@ -628,11 +628,12 @@ static ssize_t ext4_dio_write_iter(struct kiocb *iocb, struct iov_iter *from)
>  static ssize_t
>  ext4_dax_write_iter(struct kiocb *iocb, struct iov_iter *from)
>  {
> -	ssize_t ret;
> +	ssize_t ret, written;
>  	size_t count;
>  	loff_t offset;
>  	handle_t *handle;
>  	bool extend = false;
> +	bool need_trunc = true;
>  	struct inode *inode = file_inode(iocb->ki_filp);
>  
>  	if (iocb->ki_flags & IOCB_NOWAIT) {
> @@ -668,10 +669,36 @@ ext4_dax_write_iter(struct kiocb *iocb, struct iov_iter *from)
>  
>  	ret = dax_iomap_rw(iocb, from, &ext4_iomap_ops);
>  
> -	if (extend) {
> -		ret = ext4_handle_inode_extension(inode, offset, ret);
> -		ext4_inode_extension_cleanup(inode, ret < (ssize_t)count);
> +	if (!extend)
> +		goto out;
> +
> +	if (ret <= 0)
> +		goto err_trunc;
> +
> +	written = ret;
> +	handle = ext4_journal_start(inode, EXT4_HT_INODE, 2);
> +	if (IS_ERR(handle)) {
> +		ret = PTR_ERR(handle);
> +		goto err_trunc;
>  	}
> +
> +	if (ext4_update_inode_size(inode, offset + written)) {
> +		ret = ext4_mark_inode_dirty(handle, inode);
> +		if (unlikely(ret)) {
> +			ext4_journal_stop(handle);
> +			goto err_trunc;
> +		}
> +	}
> +
> +	if (written == count)
> +		need_trunc = false;
> +
> +	if (inode->i_nlink)
> +		ext4_orphan_del(handle, inode);

Why did you keep ext4_orphan_del() here? I thought the whole point of this
patch is to avoid it? In fact, rather then opencoding
ext4_handle_inode_extension() I'd add argument to
ext4_handle_inode_extension() like:

ext4_handle_inode_extension(inode, pos, written, allocated)

and remove inode from the orphan list only if written == allocated. The
call site in ext4_dio_write_end_io() would call:

	/*
	 * For DIO we don't do partial writes so we must have submitted all
	 * that was allocated.
	 */
	return ext4_handle_inode_extension(inode, pos, size, size);

and the call site in ext4_dax_write_iter() would call:

	ret = ext4_handle_inode_extension(inode, offset, ret, count);

What do you think?

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR