Not sure where to send this. Let me know if another list is better. If this is more helpful with a snapshot kernel instead of the one I compiled let me know that as well.
Michael Jun 1 16:17:10 ports /bsd: 1st 0xffffffff81d179b0 &sched_lock (&sched_lock) @ /usr/src/sys/kern/kern_synch.c:444 Jun 1 16:17:10 ports /bsd: 2nd 0xffff800000281270 &dev_priv->irq_lock (&dev_priv->irq_lock) @ /usr/src/sys/dev/pci/drm/i915/intel_lrc.c:1645 Jun 1 16:17:10 ports /bsd: lock order "&dev_priv->irq_lock"(mutex) -> "&sched_lock"(sched_lock) first seen at: Jun 1 16:17:10 ports /bsd: #0 witness_checkorder+0x494 Jun 1 16:17:10 ports /bsd: #1 ___mp_lock+0x70 Jun 1 16:17:10 ports /bsd: #2 wakeup_n+0x39 Jun 1 16:17:10 ports /bsd: #3 task_add+0x85 Jun 1 16:17:10 ports /bsd: #4 gen6_rps_boost+0x110 Jun 1 16:17:10 ports /bsd: #5 __i915_wait_request+0x137 Jun 1 16:17:10 ports /bsd: #6 i915_gem_object_wait_rendering__nonblocking+0x1c6 Jun 1 16:17:10 ports /bsd: #7 i915_gem_set_domain_ioctl+0xce Jun 1 16:17:10 ports /bsd: #8 drm_do_ioctl+0x203 Jun 1 16:17:10 ports /bsd: #9 drmioctl+0xe9 Jun 1 16:17:10 ports /bsd: #10 VOP_IOCTL+0x4d Jun 1 16:17:10 ports /bsd: #11 vn_ioctl+0x5e Jun 1 16:17:10 ports /bsd: #12 sys_ioctl+0x439 Jun 1 16:17:10 ports /bsd: #13 syscall+0x31d Jun 1 16:17:10 ports /bsd: #14 Xsyscall_untramp+0xc0 Jun 1 16:17:10 ports /bsd: lock order "&sched_lock"(sched_lock) -> "&dev_priv->irq_lock"(mutex) first seen at: Jun 1 16:17:10 ports /bsd: #0 witness_checkorder+0x494 Jun 1 16:17:10 ports /bsd: #1 _mtx_enter+0x31 Jun 1 16:17:10 ports /bsd: #2 gen8_logical_ring_put_irq+0x36 Jun 1 16:17:10 ports /bsd: #3 __i915_wait_request+0x344 Jun 1 16:17:10 ports /bsd: #4 i915_gem_object_wait_rendering__nonblocking+0x1c6 Jun 1 16:17:10 ports /bsd: #5 i915_gem_set_domain_ioctl+0xce Jun 1 16:17:10 ports /bsd: #6 drm_do_ioctl+0x203 Jun 1 16:17:10 ports /bsd: #7 drmioctl+0xe9 Jun 1 16:17:10 ports /bsd: #8 VOP_IOCTL+0x4d Jun 1 16:17:10 ports /bsd: #9 vn_ioctl+0x5e Jun 1 16:17:10 ports /bsd: #10 sys_ioctl+0x439 Jun 1 16:17:10 ports /bsd: #11 syscall+0x31d Jun 1 16:17:10 ports /bsd: #12 Xsyscall_untramp+0xc0