BUG: unable to handle kernel NULL pointer dereference at 0000009c

I had finished doing some work in a chroot, had exited it, and issued the command "umount -a", rather than individually umount each of the mounted elements. That killed X completely and gave a screenful of error messages. I was able to reboot using the alt-sysrq REISUB sequence.

If this is an illegal command in the circumstances, I would have expected to get a warning of some kind, or have the command blocked altogether.

The machine is an EeePC 900, and the system is a fully-updated version of 12.04 (non-pae kernel) running gnome-fallback.

ProblemType: KernelOops
DistroRelease: Ubuntu 12.04
Package: linux-image-3.2.0-18-generic 3.2.0-18.28
ProcVersionSignature: Ubuntu 3.2.0-18.28-generic 3.2.9
Uname: Linux 3.2.0-18-generic i686
AlsaVersion: Advanced Linux Sound Architecture Driver Version 1.0.24.
Annotation: Your system might become unstable now and might need to be restarted.
AplayDevices:
 **** List of PLAYBACK Hardware Devices ****
 card 0: Intel [HDA Intel], device 0: ALC662 rev1 Analog [ALC662 rev1 Analog]
   Subdevices: 1/1
   Subdevice #0: subdevice #0
ApportVersion: 1.94-0ubuntu1
Architecture: i386
ArecordDevices:
 **** List of CAPTURE Hardware Devices ****
 card 0: Intel [HDA Intel], device 0: ALC662 rev1 Analog [ALC662 rev1 Analog]
   Subdevices: 1/1
   Subdevice #0: subdevice #0
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC0: ja 1618 F.... pulseaudio
CRDA: Error: command ['iw', 'reg', 'get'] failed with exit code 1: nl80211 not found.
Card0.Amixer.info:
 Card hw:0 'Intel'/'HDA Intel at 0xf7eb8000 irq 44'
   Mixer name : 'Realtek ALC662 rev1'
   Components : 'HDA:10ec0662,10438337,00100101'
   Controls : 20
   Simple ctrls : 11
CurrentDmesg:

Date: Wed Mar 7 07:57:54 2012
Failure: oops
HibernationDevice: RESUME=UUID=f1a0537c-5454-47d0-be4b-44c916978365
InstallationMedia: Ubuntu 11.10 "Oneiric Ocelot" - Release i386 (20111011)
IwConfig:
 lo no wireless extensions.

 eth0 no wireless extensions.
MachineType: ASUSTeK Computer INC. 900
ProcFB: 0 inteldrmfb
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.2.0-18-generic root=UUID=f1b69783-76f9-4736-a5d1-38b520d82063 ro quiet splash
PulseSinks: Error: command ['pacmd', 'list-sinks'] failed with exit code 1: No PulseAudio daemon running, or not running as session daemon.
PulseSources: Error: command ['pacmd', 'list-sources'] failed with exit code 1: No PulseAudio daemon running, or not running as session daemon.
RelatedPackageVersions: kerneloops-daemon 0.12+git20090217-1ubuntu18
RfKill:
 0: eeepc-wlan: Wireless LAN
  Soft blocked: yes
  Hard blocked: no
SourcePackage: linux
Title: BUG: unable to handle kernel NULL pointer dereference at 0000009c
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 03/03/2009
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: 1006
dmi.board.asset.tag: To Be Filled By O.E.M.
dmi.board.name: 900
dmi.board.vendor: ASUSTeK Computer INC.
dmi.board.version: x.xx
dmi.chassis.asset.tag: 0x00000000
dmi.chassis.type: 10
dmi.chassis.vendor: ASUSTek Computer INC.
dmi.chassis.version: x.x
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvr1006:bd03/03/2009:svnASUSTeKComputerINC.:pn900:pvr0405:rvnASUSTeKComputerINC.:rn900:rvrx.xx:cvnASUSTekComputerINC.:ct10:cvrx.x:
dmi.product.name: 900
dmi.product.version: 0405
dmi.sys.vendor: ASUSTeK Computer INC.