drm/tests: Handle EDEADLK in drm_test_check_valid_clones()

Fedora/CentOS/RHEL CI is reporting intermittent failures while running
the drm_test_check_valid_clones() KUnit test.

The error log can be either [1]:

    # drm_test_check_valid_clones: ASSERTION FAILED at
    # drivers/gpu/drm/tests/drm_atomic_state_test.c:295
    Expected ret == param->expected_result, but
        ret == -35 (0xffffffffffffffdd)
        param->expected_result == 0 (0x0)

Or [2] depending on the test case:

    # drm_test_check_valid_clones: ASSERTION FAILED at
    # drivers/gpu/drm/tests/drm_atomic_state_test.c:295
    Expected ret == param->expected_result, but
        ret == -35 (0xffffffffffffffdd)
        param->expected_result == -22 (0xffffffffffffffea)

Restart the atomic sequence when EDEADLK is returned.

[1] https://s3.amazonaws.com/arr-cki-prod-trusted-artifacts/trusted-artifacts/2113057246/test_x86_64/11802139999/artifacts/jobwatch/logs/recipes/19824965/tasks/204347800/results/946112713/logs/dmesg.log
[2] https://s3.amazonaws.com/arr-cki-prod-trusted-artifacts/trusted-artifacts/2106744297/test_aarch64/11762450907/artifacts/jobwatch/logs/recipes/19797942/tasks/204139727/results/945094561/logs/dmesg.log

Fixes: 88849f2 ("drm/tests: Add test for drm_atomic_helper_check_modeset()")
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/20251104102535.12212-1-jose.exposito89@gmail.com

Author: JoseExposito

drivers/gpu/drm/tests/drm_atomic_state_test.c

@@ -283,7 +283,14 @@ static void drm_test_check_valid_clones(struct kunit *test)
 	state = drm_kunit_helper_atomic_state_alloc(test, drm, &ctx);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, state);
 
+retry:
 	crtc_state = drm_atomic_get_crtc_state(state, priv->crtc);
+	if (PTR_ERR(crtc_state) == -EDEADLK) {
+		drm_atomic_state_clear(state);
+		ret = drm_modeset_backoff(&ctx);
+		if (!ret)
+			goto retry;
+	}
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, crtc_state);
 
 	crtc_state->encoder_mask = param->encoder_mask;
@@ -292,6 +299,12 @@ static void drm_test_check_valid_clones(struct kunit *test)
 	crtc_state->mode_changed = true;
 
 	ret = drm_atomic_helper_check_modeset(drm, state);
+	if (ret == -EDEADLK) {
+		drm_atomic_state_clear(state);
+		ret = drm_modeset_backoff(&ctx);
+		if (!ret)
+			goto retry;
+	}
 	KUNIT_ASSERT_EQ(test, ret, param->expected_result);
 
 	drm_modeset_drop_locks(&ctx);