Hello,

i've got the same :

Aug 23 08:11:39 Alphonse kernel: [50796.040046] radeon 0000:01:05.0: GPU 
lockup CP stall for more than 10000msec
Aug 23 08:11:39 Alphonse kernel: [50796.040049] ------------[ cut here 
]------------
Aug 23 08:11:39 Alphonse kernel: [50796.040072] WARNING: at 
/build/buildd/linux-2.6.38/drivers/gpu/drm/radeon/radeon_fence.c:248 
radeon_fence_wait+0x36f/0x3e0 [radeon]()
Aug 23 08:11:39 Alphonse kernel: [50796.040074] Hardware name: System 
Product Name
Aug 23 08:11:39 Alphonse kernel: [50796.040076] GPU lockup (waiting for 
0x001C093E last fence id 0x001C093B)
Aug 23 08:11:39 Alphonse kernel: [50796.040077] Modules linked in: 
usb_storage uas binfmt_misc dm_crypt snd_hda_codec_hdmi 
snd_hda_codec_via snd_hda_intel snd_seq_midi snd_rawmidi snd_hda_codec 
psmouse serio_raw snd_seq_midi_event lp asus_atk0110 snd_seq snd_hwdep 
snd_pcm edac_core edac_mce_amd k10temp ppdev sp5100_tco joydev snd_timer 
snd_seq_device i2c_piix4 shpchp snd soundcore snd_page_alloc parport_pc 
parport btrfs zlib_deflate libcrc32c radeon hid_logitech ff_memless ttm 
drm_kms_helper usbhid hid drm r8169 i2c_algo_bit ahci libahci 
pata_atiixp [last unloaded: kvm]
Aug 23 08:11:39 Alphonse kernel: [50796.040101] Pid: 5686, comm: compiz 
Not tainted 2.6.38-11-generic #48-Ubuntu
Aug 23 08:11:39 Alphonse kernel: [50796.040102] Call Trace:
Aug 23 08:11:39 Alphonse kernel: [50796.040108]  [<ffffffff81065cbf>] ? 
warn_slowpath_common+0x7f/0xc0
Aug 23 08:11:39 Alphonse kernel: [50796.040111]  [<ffffffff81065db6>] ? 
warn_slowpath_fmt+0x46/0x50
Aug 23 08:11:39 Alphonse kernel: [50796.040122]  [<ffffffffa01007cf>] ? 
radeon_fence_wait+0x36f/0x3e0 [radeon]
Aug 23 08:11:39 Alphonse kernel: [50796.040125]  [<ffffffff81087fb0>] ? 
autoremove_wake_function+0x0/0x40
Aug 23 08:11:39 Alphonse kernel: [50796.040136]  [<ffffffffa01010b1>] ? 
radeon_sync_obj_wait+0x11/0x20 [radeon]
Aug 23 08:11:39 Alphonse kernel: [50796.040142]  [<ffffffffa0066b0d>] ? 
ttm_bo_wait+0xfd/0x1b0 [ttm]
Aug 23 08:11:39 Alphonse kernel: [50796.040146]  [<ffffffffa00697e6>] ? 
ttm_bo_move_accel_cleanup+0x1c6/0x260 [ttm]
Aug 23 08:11:39 Alphonse kernel: [50796.040157]  [<ffffffffa010136f>] ? 
radeon_move_blit.clone.0+0x11f/0x180 [radeon]
Aug 23 08:11:39 Alphonse kernel: [50796.040168]  [<ffffffffa0101685>] ? 
radeon_move_ram_vram.clone.2+0x125/0x150 [radeon]
Aug 23 08:11:39 Alphonse kernel: [50796.040171]  [<ffffffff81124517>] ? 
vma_prio_tree_next+0x47/0x70
Aug 23 08:11:39 Alphonse kernel: [50796.040176]  [<ffffffffa006c3db>] ? 
ttm_eu_list_ref_sub+0x3b/0x60 [ttm]
Aug 23 08:11:39 Alphonse kernel: [50796.040187]  [<ffffffffa0101898>] ? 
radeon_bo_move+0x1e8/0x1f0 [radeon]
Aug 23 08:11:39 Alphonse kernel: [50796.040191]  [<ffffffffa006789e>] ? 
ttm_bo_handle_move_mem+0x12e/0x3d0 [ttm]
Aug 23 08:11:39 Alphonse kernel: [50796.040196]  [<ffffffffa0068982>] ? 
ttm_bo_move_buffer+0x142/0x160 [ttm]
Aug 23 08:11:39 Alphonse kernel: [50796.040200]  [<ffffffffa006c3db>] ? 
ttm_eu_list_ref_sub+0x3b/0x60 [ttm]
Aug 23 08:11:39 Alphonse kernel: [50796.040205]  [<ffffffffa0068a36>] ? 
ttm_bo_validate+0x96/0x120 [ttm]
Aug 23 08:11:39 Alphonse kernel: [50796.040215]  [<ffffffffa010283c>] ? 
radeon_bo_list_validate+0x7c/0xe0 [radeon]
Aug 23 08:11:39 Alphonse kernel: [50796.040228]  [<ffffffffa011b6c6>] ? 
radeon_cs_parser_relocs+0x236/0x270 [radeon]
Aug 23 08:11:39 Alphonse kernel: [50796.040240]  [<ffffffffa011bb51>] ? 
radeon_cs_ioctl+0xa1/0x1e0 [radeon]
Aug 23 08:11:39 Alphonse kernel: [50796.040243]  [<ffffffff811309da>] ? 
handle_pte_fault+0xfa/0x210
Aug 23 08:11:39 Alphonse kernel: [50796.040253]  [<ffffffffa002e384>] ? 
drm_ioctl+0x3e4/0x4c0 [drm]
Aug 23 08:11:39 Alphonse kernel: [50796.040265]  [<ffffffffa011bab0>] ? 
radeon_cs_ioctl+0x0/0x1e0 [radeon]
Aug 23 08:11:39 Alphonse kernel: [50796.040268]  [<ffffffff815c71b8>] ? 
do_page_fault+0x258/0x540
Aug 23 08:11:39 Alphonse kernel: [50796.040271]  [<ffffffff811764ff>] ? 
do_vfs_ioctl+0x8f/0x360
Aug 23 08:11:39 Alphonse kernel: [50796.040273]  [<ffffffff81176861>] ? 
sys_ioctl+0x91/0xa0
Aug 23 08:11:39 Alphonse kernel: [50796.040276]  [<ffffffff8100c002>] ? 
system_call_fastpath+0x16/0x1b
Aug 23 08:11:39 Alphonse kernel: [50796.040278] ---[ end trace 
521f8d8d4b5018a8 ]---