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

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