Similar problem, described in:
https://bugs.freedesktop.org/show_bug.cgi?id=100567#c18

Call Trace:
 __schedule+0x29e/0x840
 schedule+0x2c/0x80
 schedule_timeout+0x258/0x360
 ? nv50_wndw_atomic_destroy_state+0x1d/0x20 [nouveau]
 dma_fence_default_wait+0x1fc/0x260
 ? dma_fence_release+0xa0/0xa0
 dma_fence_wait_timeout+0x3e/0xf0
 drm_atomic_helper_wait_for_fences+0x3f/0xc0 [drm_kms_helper]
 nv50_disp_atomic_commit_tail+0x78/0x860 [nouveau]
 ? __switch_to_asm+0x40/0x70
 ? __switch_to_asm+0x34/0x70
 nv50_disp_atomic_commit_work+0x12/0x20 [nouveau]
 process_one_work+0x20f/0x3c0
 worker_thread+0x34/0x400
 kthread+0x120/0x140
 ? pwq_unbound_release_workfn+0xd0/0xd0
 ? kthread_bind+0x40/0x40
 ret_from_fork+0x35/0x40

Full log: https://gist.github.com/kenorb/5b95caa1694dbf7f030ccc808a110856