Re: [PATCH 1/5] ext4: ext4_split_extent shoult take care about extent zeroout v3

[Jan Kara <jack@suse.cz>]

On Mon 25-02-13 20:07:39, Dmitry Monakhov wrote:
> When ext4_split_extent_at() ends up doing zeroout & conversion to
> initialized instead of split & conversion, ext4_split_extent() gets
> confused and can wrongly mark the extent back as uninitialized resulting in
> end IO code getting confused from large unwritten extents and may result in
> data loss.
> 
> The example of problematic behavior is:
> 			    lblk len              lblk len
>   ext4_split_extent() (ex=[1000,30,uninit], map=[1010,10])
>     ext4_split_extent_at() (split [1000,30,uninit] at 1020)
>       ext4_ext_insert_extent() -> ENOSPC
>       ext4_ext_zeroout()
> 	 -> extent [1000,30] is now initialized
>     ext4_split_extent_at() (split [1000,30,init] at 1010,
> 			     MARK_UNINIT1 | MARK_UNINIT2)
>       -> extent is split and parts marked as uninitialized
> 
> Fix the problem by rechecking extent type after the first
> ext4_split_extent_at() returns. None of split_flags can not be applied to
> initialized extent so this patch also add BUG_ON to prevent similar issues
> in future.
> 
> TESTCASE: https://github.com/dmonakhov/xfstests/commit/b8a55eb5ce28c6ff29e620ab090902fcd5833597
> 
> Changes since V2: Patch no longer depends on Jan's "disable-uninit-ext-mergring" patch.
  Looks good. You can add:
Reviewed-by: Jan Kara <jack@suse.cz>

								Honza

> 
> Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
> ---
>  fs/ext4/extents.c |   22 ++++++++++++++++------
>  1 files changed, 16 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index 372b2cb..3bd3ca5 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -2943,6 +2943,10 @@ static int ext4_split_extent_at(handle_t *handle,
>  	newblock = split - ee_block + ext4_ext_pblock(ex);
>  
>  	BUG_ON(split < ee_block || split >= (ee_block + ee_len));
> +	BUG_ON(!ext4_ext_is_uninitialized(ex) &&
> +	       split_flag & (EXT4_EXT_MAY_ZEROOUT |
> +			     EXT4_EXT_MARK_UNINIT1 |
> +			     EXT4_EXT_MARK_UNINIT2));
>  
>  	err = ext4_ext_get_access(handle, inode, path + depth);
>  	if (err)
> @@ -3061,19 +3065,25 @@ static int ext4_split_extent(handle_t *handle,
>  		if (err)
>  			goto out;
>  	}
> -
> +	/*
> +	 * Update path is required because previous ext4_split_extent_at() may
> +	 * result in split of original leaf or extent zeroout.
> +	 */
>  	ext4_ext_drop_refs(path);
>  	path = ext4_ext_find_extent(inode, map->m_lblk, path);
>  	if (IS_ERR(path))
>  		return PTR_ERR(path);
> +	depth = ext_depth(inode);
> +	ex = path[depth].p_ext;
> +	uninitialized = ext4_ext_is_uninitialized(ex);
> +	split_flag1 = 0;
>  
>  	if (map->m_lblk >= ee_block) {
> -		split_flag1 = split_flag & (EXT4_EXT_MAY_ZEROOUT |
> -					    EXT4_EXT_DATA_VALID2);
> -		if (uninitialized)
> +		split_flag1 = split_flag & EXT4_EXT_DATA_VALID2;
> +		if (uninitialized) {
>  			split_flag1 |= EXT4_EXT_MARK_UNINIT1;
> -		if (split_flag & EXT4_EXT_MARK_UNINIT2)
> -			split_flag1 |= EXT4_EXT_MARK_UNINIT2;
> +			split_flag1 |= split_flag & (EXT4_EXT_MAY_ZEROOUT | EXT4_EXT_MARK_UNINIT2);
> +		}
>  		err = ext4_split_extent_at(handle, inode, path,
>  				map->m_lblk, split_flag1, flags);
>  		if (err)
> -- 
> 1.7.1
> 
-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR