From: Mingming Cao <cmm@us.ibm.com>
Subject: Re: ext4_ext_convert_to_initialized bug found in extended FSX
 testing
Date: Wed, 11 May 2011 18:15:35 -0700
Message-ID: <1305162935.4102.13.camel@mingming-laptop>
References: <4DC97C32.2020203@linux.vnet.ibm.com>
	 <BANLkTi=jjVcy9WQvNfYwPVNw-+t4M5WbFw@mail.gmail.com>
Mime-Version: 1.0
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 7bit
Cc: Allison Henderson <achender@linux.vnet.ibm.com>,
	Ext4 Developers List <linux-ext4@vger.kernel.org>
To: Yongqiang Yang <xiaoqiangnk@gmail.com>
In-Reply-To: <BANLkTi=jjVcy9WQvNfYwPVNw-+t4M5WbFw@mail.gmail.com>
Sender: linux-ext4-owner@vger.kernel.org

On Wed, 2011-05-11 at 09:47 +0800, Yongqiang Yang wrote:
> On Wed, May 11, 2011 at 1:56 AM, Allison Henderson
> <achender@linux.vnet.ibm.com> wrote:
> > Hi All,
> >
> > We've been trying to get punch hole through some extended fsx tests, and I ran across some other tests that were failing because the test file contained zeros where it shouldn't.  I made this fix to the ext4_ext_convert_to_initialized
> 
> What do you mean zeros here?
> Some useful data is zeroed?
> 
> and the test has been running smooth for about an hour now.
> Yongqiang, this one looks like it may have been associated with the
> split extents clean up patch.  Would you mind taking a look at this
> fix and giving it your ok if it looks good?  Thx!
> >
> > Signed-off-by: Allison Henderson <achender@us.ibm.com>
> > ---
> > :100644 100644 e363f21... ce69450... M  fs/ext4/extents.c
> >  fs/ext4/extents.c |    3 ++-
> >  1 files changed, 2 insertions(+), 1 deletions(-)
> >
> > diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> > index e363f21..ce69450 100644
> > --- a/fs/ext4/extents.c
> > +++ b/fs/ext4/extents.c
> > @@ -2819,7 +2819,8 @@ static int ext4_ext_convert_to_initialized(handle_t *handle,
> >                        /* case 3 */
> >                        zero_ex.ee_block =
> >                                         cpu_to_le32(map->m_lblk + map->m_len);
> > -                       zero_ex.ee_len = cpu_to_le16(allocated - map->m_len);
> > +                       zero_ex.ee_len = cpu_to_le16(ee_len -
> > +                                               allocated - map->m_len);
> The logic is that we splits [ee_block, ee_block + ee_len) into
> [ee_block, map->m_blk) that is uninitialized and [map->m_blk, ee_block
> + ee_len) that is initialized.   We need to zero [map->m_lblk +
> map->m_len, ee_block + ee_len).
> and [map->m_lblk, map->m_lblk + map->m_len) is zeroed by upper layer
> because of MAP_NEW flag.
> 
> Right logic?
> 

Hmm, the logic in case 3 is-- if ex2[map->m_blk, map->m_blk+m_len] and
ex3 together[map->mblk+m_len+1, map->m_blk+allocated] total length
(allocated)is < than 7 blocks, then we zero out the entire ex2 and ext3,
there is no need to do split.

I think zero_ex.ee_len should be "allocated". Look at the original code
(before the extents splits cleanup patches), it will zero out entire 
[map->mblk, map->m_blk+allocated] and don't do split anymore.


something like this, not a patch, but show what I think the right fix.


       if (allocated > map->m_len) {
               if (allocated <= EXT4_EXT_ZERO_LEN &&
                   (EXT4_EXT_MAY_ZEROOUT & split_flag)) {
                       /* case 3 */
                       zero_ex.ee_block =
                                        cpu_to_le32(map->m_lblk + map->m_len);
-                       zero_ex.ee_len = cpu_to_le16(allocated - map->m_len);
                       zero_ex.ee_len = cpu_to_le16(allocated);
                       ext4_ext_store_pblock(&zero_ex,
                               ext4_ext_pblock(ex) + map->m_lblk - ee_block);
                       err = ext4_ext_zeroout(inode, &zero_ex);
                        if (err)
                                goto out;
-                       split_map.m_lblk = map->m_lblk;
-                       split_map.m_len = allocated;
+             		ext4_ext_mark_initialized(ex);
+              		ext4_ext_try_to_merge(inode, path, ex);
+	              err = ext4_ext_dirty(handle, inode, path + depth);
+            		   goto out;
  }


Mingming


> 
> I can not see the error and the meaning of ee_len - allocated - map->m_len.
> 
> Thanks,
> Yongqiang.
> 
> 
> >                        ext4_ext_store_pblock(&zero_ex,
> >                                ext4_ext_pblock(ex) + map->m_lblk - ee_block);
> >                        err = ext4_ext_zeroout(inode, &zero_ex);
> > --
> > 1.7.1
> >
> >
> 
> 
>