Re: [PATCH v3 05/11] of: Add a KUnit test for overlays and test managed APIs

From: Daniel Latypov <dlatypov@google.com>
To: Stephen Boyd <sboyd@kernel.org>
Cc: Michael Turquette <mturquette@baylibre.com>,
	linux-kernel@vger.kernel.org,  linux-clk@vger.kernel.org,
	patches@lists.linux.dev,
	 Brendan Higgins <brendan.higgins@linux.dev>,
	David Gow <davidgow@google.com>,
	 Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	"Rafael J . Wysocki" <rafael@kernel.org>,
	 Rob Herring <robh+dt@kernel.org>,
	Frank Rowand <frowand.list@gmail.com>,
	 Christian Marangi <ansuelsmth@gmail.com>,
	 Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
	devicetree@vger.kernel.org,  linux-kselftest@vger.kernel.org,
	kunit-dev@googlegroups.com,  Maxime Ripard <maxime@cerno.tech>
Subject: Re: [PATCH v3 05/11] of: Add a KUnit test for overlays and test managed APIs
Date: Wed, 12 Apr 2023 17:04:26 -0700	[thread overview]
Message-ID: <CAGS_qxryWVOT9cBtKk28=NupbLP6_AiCj0P3np2GpMVKkyQOLg@mail.gmail.com> (raw)
In-Reply-To: <20230327222159.3509818-6-sboyd@kernel.org>

On Mon, Mar 27, 2023 at 3:22 PM Stephen Boyd <sboyd@kernel.org> wrote:
>
> Test the KUnit test managed overlay APIs. Confirm that platform devices
> are created and destroyed properly. This provides us confidence that the
> test managed work correctly and can be relied upon to provide tests with
> fake platform devices and device nodes via overlays compiled into the
> kernel image.
>

The discussion around kunit_cleanup() caught my eye below, so one
small comment about that.

<snip>

> +/* Test that of_overlay_apply_kunit() cleans up after the test is finished */
> +static void of_overlay_apply_kunit_cleanup(struct kunit *test)
> +{
> +       struct device *dev;
> +       struct device_node *np;
> +
> +       KUNIT_ASSERT_EQ(test, 0,
> +                       of_overlay_apply_kunit(test, kunit_overlay_test));
> +
> +       np = of_find_node_by_name(NULL, kunit_node_name);
> +       of_node_put(np); /* Not derefing 'np' after this */
> +       KUNIT_ASSERT_NOT_ERR_OR_NULL(test, np);
> +
> +       dev = bus_find_device(&platform_bus_type, NULL, np, bus_match_np);
> +       put_device(dev); /* Not derefing 'device' after this */
> +       KUNIT_ASSERT_NOT_ERR_OR_NULL(test, dev);
> +
> +       /* Remove overlay */
> +       kunit_cleanup(test);

Note: this cleans up *all* resources associated with `test`.
Right now, it's probably fine, but this probably isn't the safest approach.

Notably, two of the new/upcoming API changes rely on resource,
kunit/static_stub.h and kunit_add_action() [1].
Calling kunit_cleanup() undoes all the stubs and immediately triggers
all the actions.

Perhaps you can create your own local `struct kunit` like in [2]
E.g.

struct kunit subtest; // not sure what to call this...

kunit_init_test(&subtest, "fake test", NULL);
/* use subtest */
kunit_cleanup(&subtest);

There's also already-submitted code doing similar things in
lib/kunit/kunit-test.c you can look at, but it's in init/exit funcs.
See kunit_resource_test_init() and kunit_resource_test_exit().

[1] https://lore.kernel.org/linux-kselftest/20230331080411.981038-2-davidgow@google.com/
[2] https://lore.kernel.org/linux-kselftest/20230403201930.2019419-1-rmoar@google.com/

Daniel