linux-ext4 - Re: [PATCH] ext4: fix extent tree corruption that incurred by hole punch

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Date:	Thu, 06 Dec 2012 09:45:38 -0600
From:	Eric Sandeen <sandeen@...hat.com>
To:	Forrest Liu <forrestl@...ology.com>
CC:	"Theodore Ts'o" <tytso@....edu>,
	ext4 development <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH] ext4: fix extent tree corruption that incurred by hole
 punch

On 12/4/12 6:11 AM, Forrest Liu wrote:
> Extent indexes didn't update correctly in ext4_ext_rm_idx, when depth
> of extent tree is greater than 1.

This is interesting; we had 2 reports of similar corruption on the
list, I wonder if the application in question was doing hole punching.
I didn't expect that they were, so TBH I was pretty much ignoring
the hole-punch cases for parent index updates.  Hm.  I'll have
to look into that.

Could you turn your testcase into an xfstest regression test?

-Eric

> Signed-off-by: Forrest Liu <forrestl@...ology.com>
> ---
>  fs/ext4/extents.c |   24 ++++++++++++++++++++----
>  1 files changed, 20 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index d3dd618..b10b8c0 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -2190,13 +2190,15 @@ errout:
>   * removes index from the index block.
>   */
>  static int ext4_ext_rm_idx(handle_t *handle, struct inode *inode,
> -			struct ext4_ext_path *path)
> +			struct ext4_ext_path *path, int depth)
>  {
>  	int err;
>  	ext4_fsblk_t leaf;
> +	__le32 border;
>  
>  	/* free index block */
> -	path--;
> +	depth--;
> +	path = path + depth;
>  	leaf = ext4_idx_pblock(path->p_idx);
>  	if (unlikely(path->p_hdr->eh_entries == 0)) {
>  		EXT4_ERROR_INODE(inode, "path->p_hdr->eh_entries == 0");
> @@ -2221,6 +2223,20 @@ static int ext4_ext_rm_idx(handle_t *handle, struct inode *inode,
>  
>  	ext4_free_blocks(handle, inode, NULL, leaf, 1,
>  			 EXT4_FREE_BLOCKS_METADATA | EXT4_FREE_BLOCKS_FORGET);
> +
> +	border = path->p_idx->ei_block;
> +	while (--depth >= 0) {
> +		if (path->p_idx != EXT_FIRST_INDEX(path->p_hdr))
> +			break;
> +		path--;
> +		err = ext4_ext_get_access(handle, inode, path);
> +		if (err)
> +			break;
> +		path->p_idx->ei_block = border;
> +		err = ext4_ext_dirty(handle, inode, path);
> +		if (err)
> +			break;
> +	}
>  	return err;
>  }
>  
> @@ -2557,7 +2573,7 @@ ext4_ext_rm_leaf(handle_t *handle, struct inode *inode,
>  	/* if this leaf is free, then we should
>  	 * remove it from index block above */
>  	if (err == 0 && eh->eh_entries == 0 && path[depth].p_bh != NULL)
> -		err = ext4_ext_rm_idx(handle, inode, path + depth);
> +		err = ext4_ext_rm_idx(handle, inode, path, depth);
>  
>  out:
>  	return err;
> @@ -2760,7 +2776,7 @@ again:
>  				/* index is empty, remove it;
>  				 * handle must be already prepared by the
>  				 * truncatei_leaf() */
> -				err = ext4_ext_rm_idx(handle, inode, path + i);
> +				err = ext4_ext_rm_idx(handle, inode, path, i);
>  			}
>  			/* root level has p_bh == NULL, brelse() eats this */
>  			brelse(path[i].p_bh);
> 

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