drm/i915/selftests: Flush tasklet on wait_for_submit()

Always flush the tasklet if we have pending submissions in
wait_for_submit(), so that even if we see the HW has started before we
process its ack, when we return the execlists state is well defined.

Fixes: 06289949 ("drm/i915/selftests: Check for any sign of request starting in wait_for_submit()")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Acked-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200218211215.1336341-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gt/selftest_lrc.c

@@ -77,11 +77,11 @@ static int wait_for_submit(struct intel_engine_cs *engine,
 		cond_resched();
 		intel_engine_flush_submission(engine);
 
-		if (i915_request_is_active(rq) &&
-		    !READ_ONCE(engine->execlists.pending[0])) {
-			tasklet_unlock_wait(&engine->execlists.tasklet);
+		if (READ_ONCE(engine->execlists.pending[0]))
+			continue;
+
+		if (i915_request_is_active(rq))
 			return 0;
-		}
 
 		if (i915_request_started(rq)) /* that was quick! */
 			return 0;