linux-ext4 - Re: [PATCH] ext4: ext4_split_extent shoult take care about extent zeroout v2

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Message-ID: <87fw1csf6l.fsf@openvz.org>
Date:	Mon, 04 Feb 2013 11:37:06 +0400
From:	Dmitry Monakhov <dmonakhov@...nvz.org>
To:	Eric Sandeen <sandeen@...hat.com>
Cc:	linux-ext4@...r.kernel.org, tytso@....edu, jack@...e.cz,
	xiaoqiangnk@...il.com
Subject: Re: [PATCH] ext4: ext4_split_extent shoult take care about extent zeroout v2

On Fri, 01 Feb 2013 10:09:34 -0600, Eric Sandeen <sandeen@...hat.com> wrote:
> On 1/31/13 8:48 AM, 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/1a1c4f337d4d198803436c63a56625b1a78d8a5e
> 
> Dmitry, thanks - want to send that testcase (and any others you've collected
> that aren't in the sgi repo) to xfs@....sgi.com?

Off course. I'll a bunch of my tests this week.
> 
> Thanks,
> -Eric
> 
> > Signed-off-by: Dmitry Monakhov <dmonakhov@...nvz.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 fd51469..05222d5 100644
> > --- a/fs/ext4/extents.c
> > +++ b/fs/ext4/extents.c
> > @@ -2982,6 +2982,10 @@ 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)
> > @@ -3091,18 +3095,24 @@ 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;
> > -		if (uninitialized)
> > -			split_flag1 |= EXT4_EXT_MARK_UNINIT1;
> > -		if (split_flag & EXT4_EXT_MARK_UNINIT2)
> > -			split_flag1 |= EXT4_EXT_MARK_UNINIT2;
> > +		if (uninitialized) {
> > +			split_flag1 = EXT4_EXT_MARK_UNINIT1;
> > +			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)
> > 
> 
> --
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