drm/i915: unload: fix unpin_work related races

Kill any outstanding unpin_work when destroying the corresponding
crtc. Then flush the workqueue before the gem teardown, in case
any unpin work is still outstanding.

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index ccfc105..794d4ac 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -4850,8 +4850,22 @@
 static void intel_crtc_destroy(struct drm_crtc *crtc)
 {
 	struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
+	struct drm_device *dev = crtc->dev;
+	struct intel_unpin_work *work;
+	unsigned long flags;
+
+	spin_lock_irqsave(&dev->event_lock, flags);
+	work = intel_crtc->unpin_work;
+	intel_crtc->unpin_work = NULL;
+	spin_unlock_irqrestore(&dev->event_lock, flags);
+
+	if (work) {
+		cancel_work_sync(&work->work);
+		kfree(work);
+	}
 
 	drm_crtc_cleanup(crtc);
+
 	kfree(intel_crtc);
 }