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All,

I believe that I can pretty reliably reproduce the BUG mentioned in the
attached dmesg output. (This doesn't mean that you can, but I'll detail
what I've done here.) [This BUG is the same one that I reported last night.]

1) Create a 2 GB dynamically expanding disk.
2) Attach it to a VirtualBox machine.
3) Start the Kubuntu install process.
4) Wait until the virtual disk grows to around ~850MB. (This happens
when the install process is in the "installing packages" phase.)
5) Notice that that progress bar hasn't moved in a little while.
6) Record the BUG info from dmesg.
7) Wait around a little while more until the Kubuntu install mentions
that it has encountered an error.
8) Reboot your physical machine to kill the VirtualBox instance that now
won't shut down, but isn't actually using any CPU time. [Using xkill on
this instance results in the zombie VirtualBox process that's stuck in
IO-wait that I reported last night.]

Note that dd'ing 1GB of data to a file on disk (from /dev/zero or
/dev/urandom) does not cause an error, so this doesn't seem to be a disk
fullness thing.

More information about my machine:
I once mounted the filesystem in question with the space_cache option.
All free space numbers here are from *before* I dd'd 1GB of data onto disk.

$ btrfs fi df /
Data: total=71.23GB, used=68.16GB
System, DUP: total=8.00MB, used=24.00KB
System: total=4.00MB, used=0.00
Metadata, DUP: total=4.75GB, used=2.26GB

$ df -h /
Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/campstovevg-root
                       81G   73G  3.4G  96% /
$ mount | grep btrfs
/dev/mapper/campstovevg-root on / type btrfs (rw,relatime,ssd)

$ uname -a
Linux campstove 2.6.36+ #5 SMP PREEMPT Mon Dec 20 09:28:14 PST 2010 i686
Intel(R) Core(TM) Duo CPU L2400 @ 1.66GHz GenuineIntel GNU/Linux

~/btrfs-unstable $ git log -n1 | head -n3
commit 83a50de97fe96aca82389e061862ed760ece2283
Author: Chris Mason <chris.mason@oracle.com>
Date:   Mon Dec 13 15:06:46 2010 -0500

~/btrfs-progs-unstable $ git log -n1 | head -n3
commit 1b444cd2e6ab8dcafdd47dbaeaae369dd1517c17
Author: Chris Mason <chris.mason@oracle.com>
Date:   Wed Oct 6 09:53:38 2010 -0400


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