Update to comment #42: After leaving the computer overnight, I found it in "graphics safe mode" (or whatever it's called) the following morning. The last part of dmesg read:
[29429.364045] [drm:i915_hangcheck_elapsed] *ERROR* Hangcheck timer elapsed... GPU hung
[29429.364065] render error detected, EIR: 0x00000000
[29429.365431] [drm:i915_do_wait_request] *ERROR* i915_do_wait_request returns -5 (awaiting 13532528 at 13532527)
Thus, forcing KMS back on only results in a partially usable system for me.
Update to comment #42: After leaving the computer overnight, I found it in "graphics safe mode" (or whatever it's called) the following morning. The last part of dmesg read: hangcheck_ elapsed] *ERROR* Hangcheck timer elapsed... GPU hung do_wait_ request] *ERROR* i915_do_ wait_request returns -5 (awaiting 13532528 at 13532527)
[29429.364045] [drm:i915_
[29429.364065] render error detected, EIR: 0x00000000
[29429.365431] [drm:i915_
Thus, forcing KMS back on only results in a partially usable system for me.