Re: [RFC PATCH v2 1/3] kunit: Add kunit_add_action() to defer a call until test exit

[Maxime Ripard <maxime@cerno.tech>]

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Hi David,

Looks great, thanks for sending a second version

On Fri, Mar 31, 2023 at 04:04:09PM +0800, David Gow wrote:
> Many uses of the KUnit resource system are intended to simply defer
> calling a function until the test exits (be it due to success or
> failure). The existing kunit_alloc_resource() function is often used for
> this, but was awkward to use (requiring passing NULL init functions, etc),
> and returned a resource without incrementing its reference count, which
> -- while okay for this use-case -- could cause problems in others.
> 
> Instead, introduce a simple kunit_add_action() API: a simple function
> (returning nothing, accepting a single void* argument) can be scheduled
> to be called when the test exits. Deferred actions are called in the
> opposite order to that which they were registered.
> 
> This mimics the devres API, devm_add_action(), and also provides
> kunit_remove_action(), to cancel a deferred action, and
> kunit_release_action() to trigger one early.
> 
> This is implemented as a resource under the hood, so the ordering
> between resource cleanup and deferred functions is maintained.
> 
> Signed-off-by: David Gow <davidgow@google.com>
> ---
> 
> Changes since RFC v1:
> https://lore.kernel.org/linux-kselftest/20230325043104.3761770-2-davidgow@google.com/
> - Rename functions to better match the devm_* APIs. (Thanks Maxime)
> - Embed the kunit_resource in struct kunit_action_ctx to avoid an extra
>   allocation (Thanks Benjamin)
> - Use 'struct kunit_action_ctx' as the type for cancellation tokens
>   (Thanks Benjamin)
> - Add tests.
> 
> ---
>  include/kunit/resource.h |  89 ++++++++++++++++++++++++++++
>  lib/kunit/kunit-test.c   | 123 ++++++++++++++++++++++++++++++++++++++-
>  lib/kunit/resource.c     |  99 +++++++++++++++++++++++++++++++
>  3 files changed, 310 insertions(+), 1 deletion(-)
> 
> diff --git a/include/kunit/resource.h b/include/kunit/resource.h
> index c0d88b318e90..15efd8924666 100644
> --- a/include/kunit/resource.h
> +++ b/include/kunit/resource.h
> @@ -387,4 +387,93 @@ static inline int kunit_destroy_named_resource(struct kunit *test,
>   */
>  void kunit_remove_resource(struct kunit *test, struct kunit_resource *res);
>  
> +typedef void (*kunit_defer_function_t)(void *ctx);
> +
> +/* An opaque token to a deferred action. */
> +struct kunit_action_ctx;
> +
> +/**
> + * kunit_add_action() - Defer an 'action' (function call) until the test ends.
> + * @test: Test case to associate the action with.
> + * @func: The function to run on test exit
> + * @ctx: Data passed into @func
> + * @internal_gfp: gfp to use for internal allocations, if unsure, use GFP_KERNEL
> + *
> + * Defer the execution of a function until the test exits, either normally or
> + * due to a failure.  @ctx is passed as additional context. All functions
> + * registered with kunit_add_action() will execute in the opposite order to that
> + * they were registered in.
> + *
> + * This is useful for cleaning up allocated memory and resources.
> + *
> + * Returns:
> + *   An opaque "cancellation token", or NULL on error. Pass this token to
> + *   kunit_remove_action_token() in order to cancel the deferred execution of
> + *   func().
> + */
> +struct kunit_action_ctx *kunit_add_action(struct kunit *test, kunit_defer_function_t func,
> +		      void *ctx, gfp_t internal_gfp);

Do we expect any other context than GFP_KERNEL?

If so, then maybe we can have kunit_add_action() assume GFP_KERNEL and
add a variant for the odd case where we would actually need a different
GFP flag.

> +/**
> + * kunit_remove_action_token() - Cancel a deferred action.
> + * @test: Test case the action is associated with.
> + * @cancel_token: The cancellation token returned by kunit_add_action()
> + *
> + * Prevent an action deferred using kunit_add_action() from executing when the
> + * test ends.
> + *
> + * You can also use the (test, function, context) triplet to remove an action
> + * with kunit_remove_action().
> + */
> +void kunit_remove_action_token(struct kunit *test, struct kunit_action_ctx *cancel_token);

It's not clear to me why we still need the token. If
kunit_remove_action() works fine, why would we need to store the token?

Can't we just make kunit_add_action() return an int to indicate whether
it failed or not, and that's it?

> +/**
> + * kunit_release_action_token() - Trigger a deferred action immediately.
> + * @test: Test case the action is associated with.
> + * @cancel_token: The cancellation token returned by kunit_add_action()
> + *
> + * Execute an action immediately, instead of waiting for the test to end.
> + *
> + * You can also use the (test, function, context) triplet to trigger an action
> + * with kunit_release_action().
> + */
> +void kunit_release_action_token(struct kunit *test, struct kunit_action_ctx *cancel_token);
> +
> +/**
> + * kunit_remove_action() - Cancel a matching deferred action.
> + * @test: Test case the action is associated with.
> + * @func: The deferred function to cancel.
> + * @ctx: The context passed to the deferred function to trigger.
> + *
> + * Prevent an action deferred via kunit_add_action() from executing when the
> + * test terminates..
> + * Unlike kunit_remove_action_token(), this takes the (func, ctx) pair instead of
> + * the cancellation token. If that function/context pair was deferred multiple
> + * times, only the most recent one will be cancelled.
> + */
> +void kunit_remove_action(struct kunit *test,
> +			 kunit_defer_function_t func,
> +			 void *ctx);
> +
> +/**
> + * kunit_release_action() - Run a matching action call immediately.
> + * @test: Test case the action is associated with.
> + * @func: The deferred function to trigger.
> + * @ctx: The context passed to the deferred function to trigger.
> + *
> + * Execute a function deferred via kunit_add_action()) immediately, rather than
> + * when the test ends.
> + * Unlike kunit_release_action_token(), this takes the (func, ctx) pair instead of
> + * the cancellation token. If that function/context pair was deferred multiple
> + * times, it will only be executed once here. The most recent deferral will
> + * no longer execute when the test ends.
> + *
> + * kunit_release_action(test, func, ctx);
> + * is equivalent to
> + * func(ctx);
> + * kunit_remove_action(test, func, ctx);
> + */
> +void kunit_release_action(struct kunit *test,
> +			  kunit_defer_function_t func,
> +			  void *ctx);
>  #endif /* _KUNIT_RESOURCE_H */
> diff --git a/lib/kunit/kunit-test.c b/lib/kunit/kunit-test.c
> index b63595d3e241..eaca1b133922 100644
> --- a/lib/kunit/kunit-test.c
> +++ b/lib/kunit/kunit-test.c
> @@ -111,7 +111,7 @@ struct kunit_test_resource_context {
>  	struct kunit test;
>  	bool is_resource_initialized;
>  	int allocate_order[2];
> -	int free_order[2];
> +	int free_order[4];
>  };
>  
>  static int fake_resource_init(struct kunit_resource *res, void *context)
> @@ -402,6 +402,123 @@ static void kunit_resource_test_named(struct kunit *test)
>  	KUNIT_EXPECT_TRUE(test, list_empty(&test->resources));
>  }
>  
> +static void increment_int(void *ctx)
> +{
> +	int *i = (int *)ctx;
> +	(*i)++;
> +}
> +
> +static void kunit_resource_test_action(struct kunit *test)
> +{
> +	int num_actions = 0;
> +
> +	kunit_add_action(test, increment_int, &num_actions, GFP_KERNEL);
> +	KUNIT_EXPECT_EQ(test, num_actions, 0);
> +	kunit_cleanup(test);
> +	KUNIT_EXPECT_EQ(test, num_actions, 1);
> +
> +	/* Once we've cleaned up, the action queue is empty. */
> +	kunit_cleanup(test);
> +	KUNIT_EXPECT_EQ(test, num_actions, 1);
> +
> +	/* Check the same function can be deferred multiple times. */
> +	kunit_add_action(test, increment_int, &num_actions, GFP_KERNEL);
> +	kunit_add_action(test, increment_int, &num_actions, GFP_KERNEL);
> +	kunit_cleanup(test);
> +	KUNIT_EXPECT_EQ(test, num_actions, 3);
> +}
> +static void kunit_resource_test_remove_action(struct kunit *test)
> +{
> +	int num_actions = 0;
> +	struct kunit_action_ctx *cancel_token;
> +	struct kunit_action_ctx *cancel_token2;
> +
> +	cancel_token = kunit_add_action(test, increment_int, &num_actions, GFP_KERNEL);
> +	KUNIT_EXPECT_EQ(test, num_actions, 0);
> +
> +	kunit_remove_action_token(test, cancel_token);
> +	kunit_cleanup(test);
> +	KUNIT_EXPECT_EQ(test, num_actions, 0);
> +
> +	/* Check calls from the same function/context pair can be cancelled independently*/
> +	cancel_token = kunit_add_action(test, increment_int, &num_actions, GFP_KERNEL);
> +	cancel_token2 = kunit_add_action(test, increment_int, &num_actions, GFP_KERNEL);
> +	kunit_remove_action_token(test, cancel_token);
> +	kunit_cleanup(test);
> +	KUNIT_EXPECT_EQ(test, num_actions, 1);
> +
> +	/* Also check that we can cancel just one of the identical function/context pairs. */
> +	cancel_token = kunit_add_action(test, increment_int, &num_actions, GFP_KERNEL);
> +	cancel_token2 = kunit_add_action(test, increment_int, &num_actions, GFP_KERNEL);
> +	kunit_remove_action(test, increment_int, &num_actions);
> +	kunit_cleanup(test);
> +	KUNIT_EXPECT_EQ(test, num_actions, 2);
> +}
> +static void kunit_resource_test_release_action(struct kunit *test)
> +{
> +	int num_actions = 0;
> +	struct kunit_action_ctx *cancel_token;
> +	struct kunit_action_ctx *cancel_token2;
> +
> +	cancel_token = kunit_add_action(test, increment_int, &num_actions, GFP_KERNEL);
> +	KUNIT_EXPECT_EQ(test, num_actions, 0);
> +	/* Runs immediately on trigger. */
> +	kunit_release_action_token(test, cancel_token);
> +	KUNIT_EXPECT_EQ(test, num_actions, 1);
> +
> +	/* Doesn't run again on test exit. */
> +	kunit_cleanup(test);
> +	KUNIT_EXPECT_EQ(test, num_actions, 1);
> +
> +	/* Check calls from the same function/context pair can be triggered independently*/
> +	cancel_token = kunit_add_action(test, increment_int, &num_actions, GFP_KERNEL);
> +	cancel_token2 = kunit_add_action(test, increment_int, &num_actions, GFP_KERNEL);
> +	kunit_release_action_token(test, cancel_token);
> +	KUNIT_EXPECT_EQ(test, num_actions, 2);
> +	kunit_cleanup(test);
> +	KUNIT_EXPECT_EQ(test, num_actions, 3);
> +
> +	/* Also check that we can trigger just one of the identical function/context pairs. */
> +	kunit_add_action(test, increment_int, &num_actions, GFP_KERNEL);
> +	kunit_add_action(test, increment_int, &num_actions, GFP_KERNEL);
> +	kunit_release_action(test, increment_int, &num_actions);
> +	KUNIT_EXPECT_EQ(test, num_actions, 4);
> +	kunit_cleanup(test);
> +	KUNIT_EXPECT_EQ(test, num_actions, 5);
> +}
> +static void action_order_1(void *ctx)
> +{
> +	struct kunit_test_resource_context *res_ctx = (struct kunit_test_resource_context *)ctx;
> +
> +	KUNIT_RESOURCE_TEST_MARK_ORDER(res_ctx, free_order, 1);
> +	kunit_log(KERN_INFO, current->kunit_test, "action_order_1");
> +}
> +static void action_order_2(void *ctx)
> +{
> +	struct kunit_test_resource_context *res_ctx = (struct kunit_test_resource_context *)ctx;
> +
> +	KUNIT_RESOURCE_TEST_MARK_ORDER(res_ctx, free_order, 2);
> +	kunit_log(KERN_INFO, current->kunit_test, "action_order_2");
> +}
> +static void kunit_resource_test_action_ordering(struct kunit *test)
> +{
> +	struct kunit_test_resource_context *ctx = test->priv;
> +	struct kunit_action_ctx *cancel_token;
> +
> +	kunit_add_action(test, action_order_1, ctx, GFP_KERNEL);
> +	cancel_token = kunit_add_action(test, action_order_2, ctx, GFP_KERNEL);
> +	kunit_add_action(test, action_order_1, ctx, GFP_KERNEL);
> +	kunit_add_action(test, action_order_2, ctx, GFP_KERNEL);
> +	kunit_remove_action(test, action_order_1, ctx);
> +	kunit_release_action_token(test, cancel_token);
> +	kunit_cleanup(test);
> +
> +	/* [2 is triggered] [2], [(1 is cancelled)] [1] */
> +	KUNIT_EXPECT_EQ(test, ctx->free_order[0], 2);
> +	KUNIT_EXPECT_EQ(test, ctx->free_order[1], 2);
> +	KUNIT_EXPECT_EQ(test, ctx->free_order[2], 1);
> +}
> +
>  static int kunit_resource_test_init(struct kunit *test)
>  {
>  	struct kunit_test_resource_context *ctx =
> @@ -433,6 +550,10 @@ static struct kunit_case kunit_resource_test_cases[] = {
>  	KUNIT_CASE(kunit_resource_test_proper_free_ordering),
>  	KUNIT_CASE(kunit_resource_test_static),
>  	KUNIT_CASE(kunit_resource_test_named),
> +	KUNIT_CASE(kunit_resource_test_action),
> +	KUNIT_CASE(kunit_resource_test_remove_action),
> +	KUNIT_CASE(kunit_resource_test_release_action),
> +	KUNIT_CASE(kunit_resource_test_action_ordering),
>  	{}
>  };
>  
> diff --git a/lib/kunit/resource.c b/lib/kunit/resource.c
> index c414df922f34..824cf91e306d 100644
> --- a/lib/kunit/resource.c
> +++ b/lib/kunit/resource.c
> @@ -77,3 +77,102 @@ int kunit_destroy_resource(struct kunit *test, kunit_resource_match_t match,
>  	return 0;
>  }
>  EXPORT_SYMBOL_GPL(kunit_destroy_resource);
> +
> +struct kunit_action_ctx {
> +	struct kunit_resource res;
> +	kunit_defer_function_t func;
> +	void *ctx;
> +};
> +
> +static void __kunit_action_free(struct kunit_resource *res)
> +{
> +	struct kunit_action_ctx *action_ctx = container_of(res, struct kunit_action_ctx, res);
> +
> +	action_ctx->func(action_ctx->ctx);
> +}
> +
> +struct kunit_action_ctx *kunit_add_action(struct kunit *test, kunit_defer_function_t func,
> +					 void *ctx, gfp_t internal_gfp)
> +{
> +	struct kunit_action_ctx *action_ctx;
> +
> +	KUNIT_ASSERT_NOT_NULL_MSG(test, func, "Tried to action a NULL function!");
> +
> +	action_ctx = kzalloc(sizeof(*action_ctx), internal_gfp);
> +	if (!action_ctx)
> +		return NULL;
> +
> +	action_ctx->func = func;
> +	action_ctx->ctx = ctx;
> +
> +	action_ctx->res.should_kfree = true;
> +	/* As init is NULL, this cannot fail. */
> +	__kunit_add_resource(test, NULL, __kunit_action_free, &action_ctx->res, action_ctx);
> +
> +	return action_ctx;
> +}

One thing worth pointing is that if kunit_add_action() fails, the
cleanup function passed as an argument won't run.

So, if the kzalloc call ever fails, patch 2 will leak its res->data()
resource for example.

devm (and drmm) handles this using a variant called
devm_add_action_or_reset, we should either provide the same variant or
just go for that behavior by default.

Maxime

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