drm/i915/execlists: Detect an out-of-order context switch

We require that the request is completed before the context is switched
away.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/20170223145031.26210-1-chris@chris-wilson.co.ukReviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>

drivers/gpu/drm/i915/intel_lrc.c

@@ -591,6 +591,7 @@ static void intel_lrc_irq_handler(unsigned long data)
 			GEM_BUG_ON(port[0].count == 0);
 			if (--port[0].count == 0) {
 				GEM_BUG_ON(status & GEN8_CTX_STATUS_PREEMPTED);
+				GEM_BUG_ON(!i915_gem_request_completed(port[0].request));
 				execlists_context_status_change(port[0].request,
 								INTEL_CONTEXT_SCHEDULE_OUT);