Date:	Thu, 12 Sep 2013 13:59:07 -0500
From:	Eric Sandeen <sandeen@...hat.com>
To:	Alexander Harrowell <a.harrowell@...il.com>
CC:	linux-ext4@...r.kernel.org
Subject: Re: Fwd: Fwd: strange e2fsck magic number behaviour

On 9/12/13 11:56 AM, Alexander Harrowell wrote:
> ---------- Forwarded message ----------
> From: Alexander Harrowell <a.harrowell@...il.com>
> Date: Thu, Sep 12, 2013 at 4:54 PM
> Subject: Re: Fwd: strange e2fsck magic number behaviour
> To: Eric Sandeen <sandeen@...hat.com>
> 
> 
> It was 63GB and I just wanted to fork over 3GB of extra space from my
> Windows partition...

Ok, so you tried to resize from 63G to 66G?  Should have been relatively
easy/safe.  I forgot to ask which version of e2fsprogs you had, but if
you did the grow online/mounted, most of the work is done in the kernel.

As Ted said, knowing more info might yield clues:

1) what e2fsprogs version?
2) what were the kernel messages when it crashed/hung?
3) what was the fsck output?

If you didn't save that stuff, it makes it harder to do a post-mortem...

> The fstab is as follows
> 
> /dev/sda1 SYSTEM_DRV ntfs 1.17g (boot)
> /dev/sda2 Windows7_OS ntfs 63.4G
> /dev/sda4 extended partition containing:
> -- /dev/sda6 swap linux-swap 8.05G
> -- /dev/sda5 /home ext4 66.14G
> /dev/sda3 Lenovo_Recovery ntfs 10.25G
> unallocated 1M
> 
> that's what was intended and is what gparted reports. (however,
> weirdly, if you ask Ubuntu Disk Utility, it says /dev/sda5 is 71GB and
> /dev/sda4 is correspondingly bigger. this I have only just noticed.)

TBH, I have no idea what Ubuntu Disk Utility does.  I'd trust fdisk -lu
output or /proc/partitions for accurate size info.

Oh; 61.14GiB (powers of 2) == 71 GB (powers of 10)

(61.14*1024*1024*1024/1000/1000/1000 = 71)

So Ubuntu Disk Utility is in cahoots w/ the drive manufacturers, and
using more favorable units.  ;)

-Eric

> kernel is 3.2.0-29-generic, machine is a ThinkPad X200s with 160GB disk.
> 
> thanks for your help.
> 
> 
> On Thu, Sep 12, 2013 at 4:44 PM, Eric Sandeen <sandeen@...hat.com> wrote:
>> On 9/12/13 11:39 AM, Alexander Harrowell wrote:
>>> I'm currently trying to recover an ext4 filesystem. Last night, during
>>> a resize operation,
>>
>> from what size to what size? On what kernel?
>>
>>> the system (Ubuntu 12.04 LTS on my fix-stuff usb
>>> stick) locked up hard and eventually crashed. Restarting,
>>> unsurprisingly, gparted offered to check the volume. e2fsck, called
>>> from within gparted, replayed the journal overnight and completed the
>>> resize.
>>
>> hmmm... perhaps.
>>
>>> however, where I was expecting a volume with about 3.5GB of free
>>> space, there was now a volume with 32GB free space, a bit more than
>>> 50% utilised. inevitably, trying to boot the linux that lives in there
>>> dropped into grub rescue.
>>>
>>> going back, I tried to e2fsck it. this reported large numbers of inode
>>> issues and eventually reported clean. I could mount the volume, but
>>> file metadata looked generally broken (lots of ?s). testdisk showed
>>> the partitions were intact, although it claimed the drive was the
>>> wrong size (incorrectly), and found lots of deleted files within my
>>> ecryptfs home folder. It also found the backup superblocks for the
>>> damaged volume.
>>>
>>> the first couple I tried were corrupt, but the third was valid. e2fsck
>>> -b [superblock] -y reports fixing a lot of inode things, checksums,
>>> and then restarts.  it then starts to report hunormous numbers of
>>> multiply-claimed blocks.
>>>
>>> and now comes the interesting bit - at some point, block 16777215
>>> starts to appear more and more often in the inodes, often duplicated,
>>> until it starts to print out the number 16777215 in a fast loop. in
>>> fact, it looks like it hits some inode and keeps printing block
>>> 16777215 to the same very long line (it's generated 500MB of log)
>>
>> = 111111111111111111111111 binary.
>>
>> Guessing it's maybe a bitmap block?
>>
>> Resize2fs has had a lot of trouble lately it seems.  You may have just
>> been the unlucky recipient of a resize2fs bug...
>>
>> -Eric
>>
>>> I removed the first inode containing this block via debugfs, without
>>> this helping.
>>>
>>> It sticks out that 16777215 is a magic number (the maximum in a 48 bit
>>> address space) and I google that either ext4 or e2fsck has had a bug
>>> involving it before.
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>>
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