drm/i915: Park the signaler before sleeping

If the signal to park arrives before we sleep, then we need to check
kthread_should_park() before sleeping to avoid missing the signal.
Otherwise, if the signal arrives whilst we are processing completed
requests, we will reset the current->state back to TASK_INTERRUPTIBLE
and so miss the wakeup.

Fixes: fe3288b5da2c ("drm/i915: Park the breadcrumbs signaler across a GPU reset")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170403105124.8969-1-chris@chris-wilson.co.uk
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

drivers/gpu/drm/i915/intel_breadcrumbs.c

@@ -629,6 +629,9 @@ static int intel_breadcrumbs_signaler(void *arg)
 		} else {
 			DEFINE_WAIT(exec);
 
+			if (kthread_should_park())
+				kthread_parkme();
+
 			if (kthread_should_stop()) {
 				GEM_BUG_ON(request);
 				break;
@@ -641,9 +644,6 @@ static int intel_breadcrumbs_signaler(void *arg)
 
 			if (request)
 				remove_wait_queue(&request->execute, &exec);
-
-			if (kthread_should_park())
-				kthread_parkme();
 		}
 		i915_gem_request_put(request);
 	} while (1);