DragonFlyBSD

Process Xorg stuck in state "lwe" with kernel saying:

WARNING ({ int start_jiffies, elapsed_jiffies, remaining_jiffies, ret; _Bool timeout_expired = 0; _Bool interrupted = 0; long retval; start_jiffies = ticks; lockmgr(&dev_priv->pending_flip_queue.lock, 0x00000002); while (1) { if (!intel_crtc_has_pending_flip(crtc)) break; ret = lksleep(&dev_priv->pending_flip_queue, &dev_priv->pending_flip_queue.lock, 0, "lwe", 60*hz); if (ret 4 || ret (1)) { interrupted = 1; break; } if (ret 35) { timeout_expired = 1; break; } } lockmgr(&dev_priv>pending_flip_queue.lock, 0x00000006); elapsed_jiffies = ticks - start_jiffies; remaining_jiffies = 60*hz - elapsed_jiffies; if (remaining_jiffies <= 0) remaining_jiffies = 1; if (timeout_expired) retval = 0; else if (interrupted) retval = -512; else if (60*hz > 0) retval = remaining_jiffies; else retval = 1; retval; }) 0 failed at /usr/src/sys/dev/drm/i915/intel_display.c:3348

error: [drm:pid1018:intel_pipe_set_base] ERROR pipe is still busy with an old pageflip

These two messages then repeat in 1 minute interval. Switching to console works (but is delayed up to that 1 minute), so the system can be rebooted cleanly.

The machine runs on Intel Celeron J1900 (ie. "<ValleyView/Baytrail> on vgapci0") with software from current dports (xorg-server-1.17.2,1 + xf86-video-intel-2.99.2015.09.09,1).

PS: I suspect this to be some race condition as I've been running "DragonFly desktop" on this machine for several days with no problem so far.