drm/i915: Skip unused contexts for context_barrier_task()

If the context has not been used yet, it needs no barrier, and in the
process fix up the selftest in mock_contexts.

Testcase: igt/gem_ctx_clone/vm
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190429090735.326-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_gem_context.c

@@ -924,15 +924,15 @@ static int context_barrier_task(struct i915_gem_context *ctx,
 	for_each_gem_engine(ce, i915_gem_context_lock_engines(ctx), it) {
 		struct i915_request *rq;
 
-		if (!(ce->engine->mask & engines))
-			continue;
-
 		if (I915_SELFTEST_ONLY(context_barrier_inject_fault &
 				       ce->engine->mask)) {
 			err = -ENXIO;
 			break;
 		}
 
+		if (!(ce->engine->mask & engines) || !ce->state)
+			continue;
+
 		rq = intel_context_create_request(ce);
 		if (IS_ERR(rq)) {
 			err = PTR_ERR(rq);

drivers/gpu/drm/i915/selftests/i915_gem_context.c

@@ -1665,7 +1665,7 @@ static int mock_context_barrier(void *arg)
 		goto out;
 	}
 	if (counter == 0) {
-		pr_err("Did not retire immediately for all inactive engines\n");
+		pr_err("Did not retire immediately for all unused engines\n");
 		err = -EINVAL;
 		goto out;
 	}