linux-kernel - Re: [PATCH v3 3/3] drm/tests: managed: Add a simple test for drmm_managed

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Message-ID: <mwdzi5424bvw57pqred3e2hcq7tp6xkaywj3dabixkbmq5hkbf@emquthxzlth3>
Date: Fri, 15 Dec 2023 17:31:38 +0100
From: Maxime Ripard <mripard@...nel.org>
To: Michał Winiarski <michal.winiarski@...el.com>
Cc: intel-xe@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org, 
	linux-kernel@...r.kernel.org, Rodrigo Vivi <rodrigo.vivi@...el.com>, 
	Michal Wajdeczko <michal.wajdeczko@...el.com>, Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
	Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, 
	Daniel Vetter <daniel@...ll.ch>, Javier Martinez Canillas <javierm@...hat.com>, 
	Maíra Canal <mcanal@...lia.com>
Subject: Re: [PATCH v3 3/3] drm/tests: managed: Add a simple test for
 drmm_managed_release

Hi,

On Mon, Dec 11, 2023 at 11:09:39PM +0100, Michał Winiarski wrote:
> Add a simple test that checks whether the action is indeed called right
> away and that it is not called on the final drm_dev_put().
> 
> Signed-off-by: Michał Winiarski <michal.winiarski@...el.com>
> ---
>  drivers/gpu/drm/tests/drm_managed_test.c | 29 ++++++++++++++++++++++++
>  1 file changed, 29 insertions(+)
> 
> diff --git a/drivers/gpu/drm/tests/drm_managed_test.c b/drivers/gpu/drm/tests/drm_managed_test.c
> index 15bd2474440b5..ef5e784afbc6d 100644
> --- a/drivers/gpu/drm/tests/drm_managed_test.c
> +++ b/drivers/gpu/drm/tests/drm_managed_test.c
> @@ -48,6 +48,34 @@ static void drm_test_managed_run_action(struct kunit *test)
>  	KUNIT_EXPECT_GT_MSG(test, ret, 0, "Release action was not called");
>  }
>  
> +/*
> + * The test verifies that the release action is called immediately when
> + * drmm_release_action is called and that it is not called for a second time
> + * when the device is released.
> + */

Thanks, it's much clearer now.

> +static void drm_test_managed_release_action(struct kunit *test)
> +{
> +	struct managed_test_priv *priv = test->priv;
> +	int ret;
> +
> +	ret = drmm_add_action_or_reset(priv->drm, drm_action, priv);
> +	KUNIT_EXPECT_EQ(test, ret, 0);
> +
> +	ret = drm_dev_register(priv->drm, 0);
> +	KUNIT_ASSERT_EQ(test, ret, 0);
> +
> +	drmm_release_action(priv->drm, drm_action, priv);
> +	KUNIT_EXPECT_TRUE_MSG(test, priv->action_done, "Release action was not called");
> +	priv->action_done = false;

We should call wait_event_* here.

> +
> +	drm_dev_unregister(priv->drm);
> +	drm_kunit_helper_free_device(test, priv->drm->dev);
> +
> +	ret = wait_event_interruptible_timeout(priv->action_wq, priv->action_done,
> +					       msecs_to_jiffies(TEST_TIMEOUT_MS));
> +	KUNIT_EXPECT_EQ_MSG(test, ret, 0, "Unexpected release action call during cleanup");
> +}
> +

Tests should in general be as fast as possible. Waiting for 100ms for
the success case is not ok. We have ~500 tests at the moment, if every
test was doing that it would take at least 50s to run all our unit
tests, while it takes less than a second at the moment on a capable
machine.

And also, I'm not sure we actually need to make sure it never happened.
If only because nothing actually guarantees it wouldn't have happened
after the timeout anyway, so the test isn't definitive.

I guess what we could test is whether the action is still in the actions
list through a function only exported to tests. If it's no longer in the
action list, then it won't be run.

But unless we ever have a bug, I'm not sure it's worth testing for that.

Maxime

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