[Natty] [BTRFS] Ugly "kernel BUG" displayed

[Swâmi Petaramesh]

On a BTRFS machine, the working Gnome session suddenly disappeared, replaced with a text screen displaying an ugly "kernel BUG" related to BTRFS (see attached picture).

I would have expected the system to be hanged, but no, pressing a key brought me back to my Gnome session, where I could shut the system down gracefully...

ProblemType: Bug
DistroRelease: Ubuntu 11.04
Package: linux-image-2.6.38-8-generic 2.6.38-8.42
ProcVersionSignature: Ubuntu 2.6.38-8.42-generic 2.6.38.2
Uname: Linux 2.6.38-8-generic i686
AlsaVersion: Advanced Linux Sound Architecture Driver Version 1.0.23.
Architecture: i386
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC0: michel 2856 F.... pulseaudio
CRDA:
 country FR:
  (2402 - 2482 @ 40), (N/A, 20)
  (5170 - 5250 @ 40), (N/A, 20)
  (5250 - 5330 @ 40), (N/A, 20), DFS
  (5490 - 5710 @ 40), (N/A, 27), DFS
Card0.Amixer.info:
 Card hw:0 'Intel'/'HDA Intel at 0xf6dfc000 irq 47'
   Mixer name : 'Silicon Image SiI1392 HDMI'
   Components : 'HDA:83847616,1028020a,00100201 HDA:10951392,1028020a,00100000'
   Controls : 31
   Simple ctrls : 19
CheckboxSubmission: 1ea6109db29b53f721a523a77b7f3abf
CheckboxSystem: d00f84de8a555815fa1c4660280da308
Date: Thu May 12 15:57:51 2011
EcryptfsInUse: Yes
HibernationDevice: RESUME=UUID=da6ff0b1-8caa-4536-bb59-93f66ebcb3c7
InstallationMedia: Ubuntu 10.04 LTS "Lucid Lynx" - Release i386 (20100429)
MachineType: Dell Inc. XPS M1330
ProcEnviron:
 LANGUAGE=fr_FR:en
 PATH=(custom, user)
 LANG=fr_FR.UTF-8
 SHELL=/bin/bash
ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-2.6.38-8-generic root=/dev/mapper/VG1-TETHYS ro rootflags=subvol=UBUNTU quiet splash vt.handoff=7
RelatedPackageVersions:
 linux-restricted-modules-2.6.38-8-generic N/A
 linux-backports-modules-2.6.38-8-generic N/A
 linux-firmware 1.52
SourcePackage: linux
UpgradeStatus: Upgraded to natty on 2011-04-03 (39 days ago)
dmi.bios.date: 12/26/2008
dmi.bios.vendor: Dell Inc.
dmi.bios.version: A15
dmi.board.name: 0N6705
dmi.board.vendor: Dell Inc.
dmi.chassis.type: 8
dmi.chassis.vendor: Dell Inc.
dmi.modalias: dmi:bvnDellInc.:bvrA15:bd12/26/2008:svnDellInc.:pnXPSM1330:pvr:rvnDellInc.:rn0N6705:rvr:cvnDellInc.:ct8:cvr:
dmi.product.name: XPS M1330
dmi.sys.vendor: Dell Inc.