`halt -p` causes error

[sw2wolf]

After `halt -p`, i get the following output:

intel drm0: gpu hung !
/etc/rc.shutdown in progress ...
/etc/rc.shutdown complete .
syncing disks ... done
uvm_fault(0xd0a047a0,0xd5b24000,0,1) -> e
kernel: page fault trap,aue=0 stopping at i915_gem_evict_inactive +0x2d:
   mov 0x6c(%ebx), %edx
ddb>

After rebooting the box, the system seems ok. What do those message mean ?

Thanks!