Re: [PATCH linux-kselftest/test v4] lib/list-test: add a test for the 'list' doubly linked list

[Dan Carpenter <dan.carpenter@oracle.com>]

On Fri, Oct 18, 2019 at 02:55:49PM -0700, David Gow wrote:
> Add a KUnit test for the kernel doubly linked list implementation in
> include/linux/list.h
> 
> Each test case (list_test_x) is focused on testing the behaviour of the
> list function/macro 'x'. None of the tests pass invalid lists to these
> macros, and so should behave identically with DEBUG_LIST enabled and
> disabled.
> 
> Note that, at present, it only tests the list_ types (not the
> singly-linked hlist_), and does not yet test all of the
> list_for_each_entry* macros (and some related things like
> list_prepare_entry).
> 
> Signed-off-by: David Gow <davidgow@google.com>
> ---
> 
> The changes from v3 are mostly to do with naming:
> - The Kconfig entry has been renamed from LIST_TEST to LIST_KUNIT_TEST,
>   which matches the SYSCTL_KUNIT_TEST entry,
> - The Kconfig description was updated to better match other KUnit tests,
>   specifying that the test is not intended for use in a production
>   kernel. A now-redundant mention of the test running a boot was
>   removed.
> - The MAINTAINERS entry refers to a "KUNIT TEST" rather than a "UNIT
>   TEST"
> - The module name has changed from "list-test" to "list-kunit-test".
> 
> Earlier versions of the test can be found:
> v3:
> https://lore.kernel.org/linux-kselftest/20191016215707.95317-1-davidgow@google.com/
> v2:
> https://lore.kernel.org/linux-kselftest/20191010185631.26541-1-davidgow@google.com/
> v1:
> https://lore.kernel.org/linux-kselftest/20191007213633.92565-1-davidgow@google.com/
> 
>  MAINTAINERS       |   5 +
>  lib/Kconfig.debug |  18 ++
>  lib/Makefile      |   3 +
>  lib/list-test.c   | 740 ++++++++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 766 insertions(+)
>  create mode 100644 lib/list-test.c
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 7ef985e01457..7ced1b69a3d3 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -9504,6 +9504,11 @@ F:	Documentation/misc-devices/lis3lv02d.rst
>  F:	drivers/misc/lis3lv02d/
>  F:	drivers/platform/x86/hp_accel.c
>  
> +LIST KUNIT TEST
> +M:	David Gow <davidgow@google.com>
> +S:	Maintained
> +F:	lib/list-test.c
> +
>  LIVE PATCHING
>  M:	Josh Poimboeuf <jpoimboe@redhat.com>
>  M:	Jiri Kosina <jikos@kernel.org>
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index a3017a5dadcd..7991b78eb1f3 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -1961,6 +1961,24 @@ config SYSCTL_KUNIT_TEST
>  
>  	  If unsure, say N.
>  
> +config LIST_KUNIT_TEST
> +	bool "KUnit Test for Kernel Linked-list structures"
> +	depends on KUNIT
> +	help
> +	  This builds the linked list KUnit test suite.
> +	  It tests that the API and basic functionality of the list_head type
> +	  and associated macros.
> +	
> +	  KUnit tests run during boot and output the results to the debug log
> +	  in TAP format (http://testanything.org/). Only useful for kernel devs
> +	  running the KUnit test harness, and not intended for inclusion into a
> +	  production build.
> +
> +	  For more information on KUnit and unit tests in general please refer
> +	  to the KUnit documentation in Documentation/dev-tools/kunit/.
> +
> +	  If unsure, say N.
> +
>  config TEST_UDELAY
>  	tristate "udelay test driver"
>  	help
> diff --git a/lib/Makefile b/lib/Makefile
> index bba1fd5485f7..890e581d00c4 100644
> --- a/lib/Makefile
> +++ b/lib/Makefile
> @@ -292,3 +292,6 @@ obj-$(CONFIG_GENERIC_LIB_MULDI3) += muldi3.o
>  obj-$(CONFIG_GENERIC_LIB_CMPDI2) += cmpdi2.o
>  obj-$(CONFIG_GENERIC_LIB_UCMPDI2) += ucmpdi2.o
>  obj-$(CONFIG_OBJAGG) += objagg.o
> +
> +# KUnit tests
> +obj-$(CONFIG_LIST_KUNIT_TEST) += list-test.o
> diff --git a/lib/list-test.c b/lib/list-test.c
> new file mode 100644
> index 000000000000..75ba3ddac959
> --- /dev/null
> +++ b/lib/list-test.c
> @@ -0,0 +1,740 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * KUnit test for the Kernel Linked-list structures.
> + *
> + * Copyright (C) 2019, Google LLC.
> + * Author: David Gow <davidgow@google.com>
> + */
> +#include <kunit/test.h>
> +
> +#include <linux/list.h>
> +
> +struct list_test_struct {
> +	int data;
> +	struct list_head list;
> +};
> +
> +static void list_test_list_init(struct kunit *test)
> +{
> +	/* Test the different ways of initialising a list. */
> +	struct list_head list1 = LIST_HEAD_INIT(list1);
> +	struct list_head list2;
> +	LIST_HEAD(list3);
> +	struct list_head *list4;
> +	struct list_head *list5;
> +
> +	INIT_LIST_HEAD(&list2);
> +
> +	list4 = kzalloc(sizeof(*list4), GFP_KERNEL);
> +	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, list4);

Why not just use GFP_KERNEL | GFP_NOFAIL and remove the check?

kzalloc() can't return error pointers.  If this were an IS_ERR_OR_NULL()
check then it would generate a static checker warning, but static
checkers don't know about KUNIT_ASSERT_NOT_ERR_OR_NULL() yet so you're
safe.

But generally NULL is a special case of success.  A common situation is
where the user deliberately disables a feature, that means it's not an
error but we also don't have a valid pointer to return because it's
disabled.

regards,
dan carpenter