drm/tests: Handle EDEADLK in set_up_atomic_state()

Fedora/CentOS/RHEL CI is reporting intermittent failures while running
the drm_validate_modeset test [1]:

    # drm_test_check_connector_changed_modeset: EXPECTATION FAILED at
    # drivers/gpu/drm/tests/drm_atomic_state_test.c:162
    Expected ret == 0, but
        ret == -35 (0xffffffffffffffdd)

Change the set_up_atomic_state() helper function to return on error and
restart the atomic sequence when the returned error is EDEADLK.

[1] https://s3.amazonaws.com/arr-cki-prod-trusted-artifacts/trusted-artifacts/2106744096/test_x86_64/11762450343/artifacts/jobwatch/logs/recipes/19797909/tasks/204139142/results/945095586/logs/dmesg.log

Fixes: 73d934d ("drm/tests: Add test for drm_atomic_helper_commit_modeset_disables()")
Closes: https://datawarehouse.cki-project.org/issue/4004
Reviewed-by: Maxime Ripard <mripard@kernel.org>
Signed-off-by: José Expósito <jose.exposito89@gmail.com>
Link: https://patch.msgid.link/20251104102535.12212-2-jose.exposito89@gmail.com

Author: JoseExposito

drivers/gpu/drm/tests/drm_atomic_state_test.c

@@ -156,24 +156,29 @@ static int set_up_atomic_state(struct kunit *test,
 
 	if (connector) {
 		conn_state = drm_atomic_get_connector_state(state, connector);
-		KUNIT_ASSERT_NOT_ERR_OR_NULL(test, conn_state);
+		if (IS_ERR(conn_state))
+			return PTR_ERR(conn_state);
 
 		ret = drm_atomic_set_crtc_for_connector(conn_state, crtc);
-		KUNIT_EXPECT_EQ(test, ret, 0);
+		if (ret)
+			return ret;
 	}
 
 	crtc_state = drm_atomic_get_crtc_state(state, crtc);
-	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, crtc_state);
+	if (IS_ERR(crtc_state))
+		return PTR_ERR(crtc_state);
 
 	ret = drm_atomic_set_mode_for_crtc(crtc_state, &drm_atomic_test_mode);
-	KUNIT_EXPECT_EQ(test, ret, 0);
+	if (ret)
+		return ret;
 
 	crtc_state->enable = true;
 	crtc_state->active = true;
 
 	if (connector) {
 		ret = drm_atomic_commit(state);
-		KUNIT_ASSERT_EQ(test, ret, 0);
+		if (ret)
+			return ret;
 	} else {
 		// dummy connector mask
 		crtc_state->connector_mask = DRM_TEST_CONN_0;
@@ -206,7 +211,13 @@ static void drm_test_check_connector_changed_modeset(struct kunit *test)
 	drm_modeset_acquire_init(&ctx, 0);
 
 	// first modeset to enable
+retry_set_up:
 	ret = set_up_atomic_state(test, priv, old_conn, &ctx);
+	if (ret == -EDEADLK) {
+		ret = drm_modeset_backoff(&ctx);
+		if (!ret)
+			goto retry_set_up;
+	}
 	KUNIT_ASSERT_EQ(test, ret, 0);
 
 	state = drm_kunit_helper_atomic_state_alloc(test, drm, &ctx);
@@ -277,7 +288,13 @@ static void drm_test_check_valid_clones(struct kunit *test)
 
 	drm_modeset_acquire_init(&ctx, 0);
 
+retry_set_up:
 	ret = set_up_atomic_state(test, priv, NULL, &ctx);
+	if (ret == -EDEADLK) {
+		ret = drm_modeset_backoff(&ctx);
+		if (!ret)
+			goto retry_set_up;
+	}
 	KUNIT_ASSERT_EQ(test, ret, 0);
 
 	state = drm_kunit_helper_atomic_state_alloc(test, drm, &ctx);