On Thu, 9 Aug 2012, Theodore Ts'o wrote:

Date: Thu, 9 Aug 2012 13:06:40 -0400
From: Theodore Ts'o <tytso@mit.edu>
To: Lukas Czerner <redacted>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
    "Linux Kernel Mailinlinux-ext4@vger.kernel.orgg List"
    [off-list ref], linux-ext4@vger.kernel.org
Subject: Re: ext4fs error
    "ext4_mb_generate_buddy:741:group 16, 8160 clusters in bitmap, 4064 in gd"
     (with repro)

On Thu, Aug 09, 2012 at 12:00:09PM +0200, Paolo Bonzini wrote:

quoted

Here is how to reproduce it.  It happens during fstrim.  I found other
occurrences of the error in the mailing list, but they were not related
to trim so they may be something different.

modprobe scsi_debug dev_size_mb=256 lbpws=1
dd if=/dev/zero of=/dev/sdb bs=1M      
fdisk /dev/sdb
 >> create a new partition accepting all defaults
fdisk -lu /dev/sdb|tail -1
 >> should show: /dev/sdb1     57      524285      262114+  83  Linux

mkfs.ext4 /dev/sdb1
mkdir test
mount /dev/sdb1 test
fstrim ./test

I can confirm that this accurately reproduces file system corruption
using a 3.5 kernel.  It looks like some block allocation bitmap blocks
is getting trimmed when it shouldn't have been.  Lukas, can you take a
look at this?

					- Ted

Hi Ted,

sorry for the delay, I've just got back from my vacation. I'll take
a look at it.

Thanks!
-Lukas