Comment 7 for bug 561538

I have this problem with a freshly installed 10.04 Desktop. Sometimes it is as easy to reproduce as: Log in as user A, log in as user B, logout user B, black screen.(Xorg log below is of this scenario) It it not 100% reproducible and there are times I cannot reproduce it at all. It seems like when I cannot reproduce it any more I need to do a cold boot before the problem comes back.

VT switching via keyboard or chvt does not do anything. Stopping and starting gdm via initctl is the only way to bring the screen back short of rebooting

The following is sometimes logged by the kernel when switching or logging out users:

May 4 10:43:04 lws-template kernel: [ 150.586572] ------------[ cut here ]------------
May 4 10:43:04 lws-template kernel: [ 150.586600] WARNING: at /build/buildd/linux-2.6.32/lib/kref.c:43 kref_get+0x2d/0x30()
May 4 10:43:04 lws-template kernel: [ 150.586609] Hardware name: SFM27
May 4 10:43:04 lws-template kernel: [ 150.586614] Modules linked in: nfs lockd nfs_acl auth_rpcgss sunrpc autofs4 binfmt_misc ppdev fbcon tileblit font bitblit softcursor vga16fb vgastate joydev i915 drm_kms_helper drm i2c_algo_bit usbhid hid psmouse serio_raw video output intel_agp lp parport r8169 mii
May 4 10:43:04 lws-template kernel: [ 150.586696] Pid: 1014, comm: Xorg Not tainted 2.6.32-21-generic #32-Ubuntu
May 4 10:43:04 lws-template kernel: [ 150.586704] Call Trace:
May 4 10:43:04 lws-template kernel: [ 150.586722] [<ffffffff81066d0b>] warn_slowpath_common+0x7b/0xc0
May 4 10:43:04 lws-template kernel: [ 150.586736] [<ffffffff81066d64>] warn_slowpath_null+0x14/0x20
May 4 10:43:04 lws-template kernel: [ 150.586748] [<ffffffff812b468d>] kref_get+0x2d/0x30
May 4 10:43:04 lws-template kernel: [ 150.586784] [<ffffffffa0094a11>] drm_gem_handle_create+0x91/0xb0 [drm]
May 4 10:43:04 lws-template kernel: [ 150.586799] [<ffffffff8153f74e>] ? mutex_lock+0x1e/0x50
May 4 10:43:04 lws-template kernel: [ 150.586838] [<ffffffffa00fcd6b>] intel_user_framebuffer_create_handle+0x1b/0x20 [i915]
May 4 10:43:04 lws-template kernel: [ 150.586872] [<ffffffffa009f22e>] drm_mode_getfb+0x7e/0xc0 [drm]
May 4 10:43:04 lws-template kernel: [ 150.586900] [<ffffffffa0092e2a>] drm_ioctl+0x27a/0x480 [drm]
May 4 10:43:04 lws-template kernel: [ 150.586931] [<ffffffffa009f1b0>] ? drm_mode_getfb+0x0/0xc0 [drm]
May 4 10:43:04 lws-template kernel: [ 150.586946] [<ffffffff81282efd>] ? apparmor_file_alloc_security+0x2d/0xa0
May 4 10:43:04 lws-template kernel: [ 150.586961] [<ffffffff81085320>] ? autoremove_wake_function+0x0/0x40
May 4 10:43:04 lws-template kernel: [ 150.586976] [<ffffffff81152a92>] vfs_ioctl+0x22/0xa0
May 4 10:43:04 lws-template kernel: [ 150.586988] [<ffffffff81152d41>] do_vfs_ioctl+0x81/0x380
May 4 10:43:04 lws-template kernel: [ 150.587001] [<ffffffff81142a82>] ? vfs_write+0x132/0x1a0
May 4 10:43:04 lws-template kernel: [ 150.587015] [<ffffffff812506da>] ? security_capable+0x2a/0x30
May 4 10:43:04 lws-template kernel: [ 150.587027] [<ffffffff81071a83>] ? capable+0x13/0x50
May 4 10:43:04 lws-template kernel: [ 150.587039] [<ffffffff811530c1>] sys_ioctl+0x81/0xa0
May 4 10:43:04 lws-template kernel: [ 150.587054] [<ffffffff810131b2>] system_call_fastpath+0x16/0x1b
May 4 10:43:04 lws-template kernel: [ 150.587064] ---[ end trace 18873645e6cf4e0f ]---

Note that there are times that the above is logged but the screen does not blank out and Xorg continues to function.

/var/log/Xorg.0.log attached. This log is up to the point where the screen blanks.

No /etc/X11/xorg.conf.

$ lspci -s 00:02.0 -nn -v
00:02.0 VGA compatible controller [0300]: Intel Corporation 82945G/GZ Integrated Graphics Controller [8086:2772] (rev 02)
 Subsystem: Holco Enterprise Co, Ltd/Shuttle Computer Device [1297:3166]
 Flags: bus master, fast devsel, latency 0, IRQ 16
 Memory at fdf00000 (32-bit, non-prefetchable) [size=512K]
 I/O ports at ff00 [size=8]
 Memory at d0000000 (32-bit, prefetchable) [size=256M]
 Memory at fdf80000 (32-bit, non-prefetchable) [size=256K]
 Capabilities: <access denied>
 Kernel driver in use: i915
 Kernel modules: i915