From: Forrest Liu <forrestl@synology.com>
Subject: Re: [PATCH] ext4: fix extent tree corruption that incurred by hole punch
Date: Sun, 9 Dec 2012 03:01:08 +0800
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Cc: Ashish Sangwan <ashishsangwan2@gmail.com>,
	"Theodore Ts'o" <tytso@mit.edu>,
	ext4 development <linux-ext4@vger.kernel.org>
To: Eric Sandeen <sandeen@redhat.com>
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2012/12/8 Eric Sandeen <sandeen@redhat.com>:
> On 12/7/12 6:26 AM, Forrest Liu wrote:
>> 2012/12/7 Ashish Sangwan <ashishsangwan2@gmail.com>:
>>> On Thu, Dec 6, 2012 at 9:18 PM, Eric Sandeen <sandeen@redhat.com> wrote:
>>>> On 12/6/12 9:45 AM, Eric Sandeen wrote:
>>>>> 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?
>>
>> Hi Eric,
>>    I will check how to do that.
>>>>
>>>> Also, please note that I sent an e2fsck patch to try to fix this
>>>> problem after the fact; it'd be great if in your testing, you could
>>>> also confirm that e2fsck w/ my patch fixes it correctly.
>>>>
>>> I checked you patch.
>>> This was the extent tree situation after removing 1st extent index:
>>> debugfs:  ex abc
>>> Level Entries       Logical        Physical Length Flags
>>>  0/ 2   1/  1     0 -  8399  32857            8400
>>>  1/ 2   1/  4  2048 -  4081   4138            2034
>>>  2/ 2   1/339  2048 -  2053  69632 -  69637      6
>>>  2/ 2   2/339  2054 -  2059  69656 -  69661      6
>>>
>>> E2fsck's output with your patch=>
>>> Linux#> /dtv/usb/sdb1/e2fsck /dev/sda1 -f
>>> e2fsck 1.42.6.1 (06-DEC-2012)
>>> Pass 1: Checking inodes, blocks, and sizes
>>> Interior extent node level 0 of inode 31:
>>> Logical start 0 does not match logical start 2048 at next level.  Fix<y>? yes
>>> Inode 31, i_blocks is 50856, should be 16280.  Fix<y>? yes
>>
>> I got similar result, pb->num_blocks is incorrect if
>> ext2fs_extent_fix_parents called.
>
> Maybe I should ask what it looks like without my patch?  I didn't
> think my patch would change anything at all about block count
> or use.
>
> -Eric
>
When i choose not to repair problem of logical start value, there have
no message like

Inode 31, i_blocks is 50856, should be 16280.  Fix<y>?

-Forrest