In raring I've found that when directly opening some png files, or somtimes when an application loads png's the Xorg freezes either completely, or sometime allows the mouse to move.
In a specific case, opening the attached png with the intel driver will cause Xorg to freeze but the the cursor will still move, but interaction is futile. System remains accessable over SSH.
The following log is found in Xorg.0.log
(EE) [mi] EQ overflowing. Additional events will be discarded until existing events are processed.
(EE)
(EE) Backtrace:
(EE) 0: /usr/bin/X (xorg_backtrace+0x3d) [0x7faf70e8550d]
(EE) 1: /usr/bin/X (mieqEnqueue+0x22b) [0x7faf70e6744b]
(EE) 2: /usr/bin/X (QueuePointerEvents+0x52) [0x7faf70d4f322]
(EE) 3: /usr/lib/xorg/modules/input/evdev_drv.so (0x7faf6ae0e000+0x566f) [0x7faf6ae1366f]
(EE) 4: /usr/bin/X (0x7faf70ce4000+0x913a8) [0x7faf70d753a8]
(EE) 5: /usr/bin/X (0x7faf70ce4000+0xb9a60) [0x7faf70d9da60]
(EE) 6: /lib/x86_64-linux-gnu/libpthread.so.0 (0x7faf6fde4000+0xfbd0) [0x7faf6fdf3bd0]
(EE) 7: /lib/x86_64-linux-gnu/libc.so.6 (ioctl+0x7) [0x7faf6eb00747]
(EE) 8: /usr/lib/x86_64-linux-gnu/libdrm.so.2 (drmIoctl+0x34) [0x7faf6fbdb344]
(EE) 9: /usr/lib/xorg/modules/drivers/intel_drv.so (0x7faf6d339000+0x3f178) [0x7faf6d378178]
(EE) 10: /usr/lib/xorg/modules/drivers/intel_drv.so (0x7faf6d339000+0xd0e18) [0x7faf6d409e18]
(EE) 11: /usr/lib/xorg/modules/drivers/intel_drv.so (0x7faf6d339000+0xd14e9) [0x7faf6d40a4e9]
(EE) 12: /usr/lib/xorg/modules/drivers/intel_drv.so (0x7faf6d339000+0xd47f8) [0x7faf6d40d7f8]
(EE) 13: /usr/lib/xorg/modules/drivers/intel_drv.so (0x7faf6d339000+0x97604) [0x7faf6d3d0604]
(EE) 14: /usr/lib/xorg/modules/drivers/intel_drv.so (0x7faf6d339000+0xd4b31) [0x7faf6d40db31]
(EE) 15: /usr/lib/xorg/modules/drivers/intel_drv.so (0x7faf6d339000+0x68a5b) [0x7faf6d3a1a5b]
(EE) 16: /usr/bin/X (0x7faf70ce4000+0x126ee1) [0x7faf70e0aee1]
(EE) 17: /usr/bin/X (0x7faf70ce4000+0x54cde) [0x7faf70d38cde]
(EE) 18: /usr/bin/X (0x7faf70ce4000+0x4431a) [0x7faf70d2831a]
(EE) 19: /lib/x86_64-linux-gnu/libc.so.6 (__libc_start_main+0xf5) [0x7faf6ea30ea5]
(EE) 20: /usr/bin/X (0x7faf70ce4000+0x44661) [0x7faf70d28661]
(EE)
(EE) [mi] These backtraces from mieqEnqueue may point to a culprit higher up the stack.
(EE) [mi] mieq is *NOT* the cause. It is a victim.
(EE) [mi] EQ overflow continuing. 100 events have been dropped.
(EE)
There is no usefull data in dmesg and
$ cat i915_error_state
no error state collected
Status changed to 'Confirmed' because the bug affects multiple users.