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

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.

Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
---
 fs/ext4/extents.c |   22 ++++++++++++++++------
 1 files changed, 16 insertions(+), 6 deletions(-)

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
>

Dmitry,

Thanks for working on these patches.  They look good!  I've dropped
them into the ext4 tree in the dev branch, and am starting to run
tests on them.

Zheng, since some of your fix up patches look like they touch some of
the code modified by Dmitry's patches, could you rebase your patch set
on top of the dev branch (which is what we've pushed to Linus plus
Dmitry's patches)?   Thanks!!

						- Ted
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On Mon, Mar 04, 2013 at 12:58:13AM -0500, Theodore Ts'o wrote:
> Dmitry,
> 
> Thanks for working on these patches.  They look good!  I've dropped
> them into the ext4 tree in the dev branch, and am starting to run
> tests on them.
> 
> Zheng, since some of your fix up patches look like they touch some of
> the code modified by Dmitry's patches, could you rebase your patch set
> on top of the dev branch (which is what we've pushed to Linus plus
> Dmitry's patches)?   Thanks!!

No problem, I will rebase my patches against the latest dev branch.

Thanks,
                                                - Zheng
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