Dec 14 16:18:20 alta kernel: [ 7811.746465] BUG: unable to handle kernel NULL pointer dereference at (null)
Dec 14 16:18:20 alta kernel: [ 7811.746476] IP: [<e09410f9>] radeon_read_ring_rptr+0x29/0x30 [radeon]
Dec 14 16:18:20 alta kernel: [ 7811.746505] *pde = 1e274067 *pte = 00000000 
Dec 14 16:18:20 alta kernel: [ 7811.746511] Oops: 0000 [#1] SMP 
Dec 14 16:18:20 alta kernel: [ 7811.746516] last sysfs file: /sys/devices/pci0000:00/0000:00:1f.5/sound/card0/controlC0/uevent
Dec 14 16:18:20 alta kernel: [ 7811.746520] Modules linked in: nfs lockd nfs_acl auth_rpcgss sunrpc binfmt_misc autofs4 snd_intel8x0 snd_ac97_codec iptable_filter ip_tables ac97_bus snd_pcm_oss snd_mixer_oss x_tables snd_pcm snd_seq_dummy snd_seq_oss snd_seq_midi snd_rawmidi snd_seq_midi_event snd_seq snd_timer snd_seq_device snd soundcore snd_page_alloc ppdev lp dell_wmi dcdbas psmouse serio_raw parport_pc shpchp parport usbhid floppy radeon ttm drm i2c_algo_bit e100 mii intel_agp agpgart
Dec 14 16:18:20 alta kernel: [ 7811.746582] 
Dec 14 16:18:20 alta kernel: [ 7811.746587] Pid: 1074, comm: Xorg Not tainted (2.6.31-15-generic #50-Ubuntu) Dimension 4600i              
Dec 14 16:18:20 alta kernel: [ 7811.746591] EIP: 0060:[<e09410f9>] EFLAGS: 00213246 CPU: 1
Dec 14 16:18:20 alta kernel: [ 7811.746606] EIP is at radeon_read_ring_rptr+0x29/0x30 [radeon]
Dec 14 16:18:20 alta kernel: [ 7811.746610] EAX: df2d7260 EBX: de331800 ECX: 00000028 EDX: 00000000
Dec 14 16:18:20 alta kernel: [ 7811.746613] ESI: e0c00000 EDI: de331800 EBP: de6d5d0c ESP: de6d5d0c
Dec 14 16:18:20 alta kernel: [ 7811.746616]  DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068
Dec 14 16:18:20 alta kernel: [ 7811.746620] Process Xorg (pid: 1074, ti=de6d4000 task=d79f25b0 task.ti=de6d4000)
Dec 14 16:18:20 alta kernel: [ 7811.746623] Stack:
Dec 14 16:18:20 alta kernel: [ 7811.746626]  de6d5d14 e0941147 de6d5d24 e0941894 de331800 00000040 de6d5d48 e0943999
Dec 14 16:18:20 alta kernel: [ 7811.746637] <0> 00000001 e09c22ed e0984857 e09c22eb de331800 de331800 de13b000 de6d5d70
Dec 14 16:18:20 alta kernel: [ 7811.746649] <0> e0944c94 00000001 e09c22ed e09847b8 e09c2342 fffffff0 de331940 de331940
Dec 14 16:18:20 alta kernel: [ 7811.746662] Call Trace:
Dec 14 16:18:20 alta kernel: [ 7811.746680]  [<e0941147>] ? radeon_get_ring_head+0x47/0x50 [radeon]
Dec 14 16:18:20 alta kernel: [ 7811.746696]  [<e0941894>] ? radeon_commit_ring+0x54/0xb0 [radeon]
Dec 14 16:18:20 alta kernel: [ 7811.746713]  [<e0943999>] ? radeon_do_cp_idle+0xc9/0x160 [radeon]
Dec 14 16:18:20 alta kernel: [ 7811.746732]  [<e0944c94>] ? radeon_do_release+0x154/0x1d0 [radeon]
Dec 14 16:18:20 alta kernel: [ 7811.746751]  [<e0948338>] ? radeon_driver_lastclose+0x58/0x60 [radeon]
Dec 14 16:18:20 alta kernel: [ 7811.746773]  [<e0842250>] ? drm_lastclose+0x40/0x2c0 [drm]
Dec 14 16:18:20 alta kernel: [ 7811.746790]  [<e0842d59>] ? drm_release+0x2e9/0x390 [drm]
Dec 14 16:18:20 alta kernel: [ 7811.746801]  [<c01e915a>] ? __fput+0xda/0x1f0
Dec 14 16:18:20 alta kernel: [ 7811.746806]  [<c01e9285>] ? fput+0x15/0x20
Dec 14 16:18:20 alta kernel: [ 7811.746811]  [<c01e56a7>] ? filp_close+0x47/0x70
Dec 14 16:18:20 alta kernel: [ 7811.746817]  [<c0146c93>] ? put_files_struct+0x63/0xb0
Dec 14 16:18:20 alta kernel: [ 7811.746822]  [<c0146d23>] ? exit_files+0x43/0x60
Dec 14 16:18:20 alta kernel: [ 7811.746826]  [<c0147dff>] ? do_exit+0x11f/0x2e0
Dec 14 16:18:20 alta kernel: [ 7811.746832]  [<c01527dd>] ? dequeue_signal+0x2d/0x170
Dec 14 16:18:20 alta kernel: [ 7811.746848]  [<e084272a>] ? drm_ioctl+0x1ea/0x360 [drm]
Dec 14 16:18:20 alta kernel: [ 7811.746853]  [<c0147ffa>] ? do_group_exit+0x3a/0xb0
Dec 14 16:18:20 alta kernel: [ 7811.746858]  [<c015403f>] ? get_signal_to_deliver+0x18f/0x300
Dec 14 16:18:20 alta kernel: [ 7811.746864]  [<c010304b>] ? do_signal+0x6b/0x160
Dec 14 16:18:20 alta kernel: [ 7811.746870]  [<c010b16a>] ? restore_i387_xstate+0xda/0x210
Dec 14 16:18:20 alta kernel: [ 7811.746878]  [<c02c7f8f>] ? security_file_permission+0xf/0x20
Dec 14 16:18:20 alta kernel: [ 7811.746884]  [<c05710b7>] ? unlock_kernel+0x27/0x30
Dec 14 16:18:20 alta kernel: [ 7811.746890]  [<c01f51bb>] ? vfs_ioctl+0x7b/0x90
Dec 14 16:18:20 alta kernel: [ 7811.746895]  [<c01f5481>] ? do_vfs_ioctl+0x71/0x310
Dec 14 16:18:20 alta kernel: [ 7811.746900]  [<c0102771>] ? restore_sigcontext+0xc1/0xe0
Dec 14 16:18:20 alta kernel: [ 7811.746905]  [<c010318d>] ? do_notify_resume+0x4d/0x60
Dec 14 16:18:20 alta kernel: [ 7811.746910]  [<c0103448>] ? work_notifysig+0x13/0x1b
Dec 14 16:18:20 alta kernel: [ 7811.746913] Code: 5d c3 55 f6 80 1e 03 00 00 08 89 e5 75 14 8b 80 e0 00 00 00 83 e2 fc 5d 03 50 10 8b 02 c3 8d 74 26 00 8b 80 e0 00 00 00 03 50 10 <8b> 02 5d c3 8d 76 00 55 8b 50 5c 89 e5 85 d2 75 36 66 83 b8 1c 
Dec 14 16:18:20 alta kernel: [ 7811.746985] EIP: [<e09410f9>] radeon_read_ring_rptr+0x29/0x30 [radeon] SS:ESP 0068:de6d5d0c
Dec 14 16:18:20 alta kernel: [ 7811.747004] CR2: 0000000000000000
Dec 14 16:18:20 alta kernel: [ 7811.747008] ---[ end trace 03b874e61d1748c2 ]---
Dec 14 16:18:20 alta kernel: [ 7811.747011] Fixing recursive fault but reboot is needed!