Re: [PATCH v14 09/18] kunit: test: add support for test abort

[shuah <shuah@kernel.org>]

On 8/23/19 10:56 AM, Brendan Higgins wrote:
> On Fri, Aug 23, 2019 at 8:36 AM shuah <shuah@kernel.org> wrote:
>>
>> Hi Brendan,
>>
>> On 8/20/19 5:20 PM, Brendan Higgins wrote:
>>> Add support for aborting/bailing out of test cases, which is needed for
>>> implementing assertions.
>>>
>>> An assertion is like an expectation, but bails out of the test case
>>> early if the assertion is not met. The idea with assertions is that you
>>> use them to state all the preconditions for your test. Logically
>>> speaking, these are the premises of the test case, so if a premise isn't
>>> true, there is no point in continuing the test case because there are no
>>> conclusions that can be drawn without the premises. Whereas, the
>>> expectation is the thing you are trying to prove.
>>>
>>> Signed-off-by: Brendan Higgins <brendanhiggins@google.com>
>>> Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>>> Reviewed-by: Logan Gunthorpe <logang@deltatee.com>
>>> Reviewed-by: Stephen Boyd <sboyd@kernel.org>
>>> ---
>>>    include/kunit/test.h      |   2 +
>>>    include/kunit/try-catch.h |  75 +++++++++++++++++++++
>>>    kunit/Makefile            |   3 +-
>>>    kunit/test.c              | 137 +++++++++++++++++++++++++++++++++-----
>>>    kunit/try-catch.c         | 118 ++++++++++++++++++++++++++++++++
>>>    5 files changed, 319 insertions(+), 16 deletions(-)
>>>    create mode 100644 include/kunit/try-catch.h
>>>    create mode 100644 kunit/try-catch.c
>>>
>>> diff --git a/include/kunit/test.h b/include/kunit/test.h
>>> index 6917b186b737a..390ce02f717b6 100644
>>> --- a/include/kunit/test.h
>>> +++ b/include/kunit/test.h
>>> @@ -10,6 +10,7 @@
>>>    #define _KUNIT_TEST_H
>>>
>>>    #include <kunit/assert.h>
>>> +#include <kunit/try-catch.h>
>>>    #include <linux/kernel.h>
>>>    #include <linux/slab.h>
>>>    #include <linux/types.h>
>>> @@ -167,6 +168,7 @@ struct kunit {
>>>
>>>        /* private: internal use only. */
>>>        const char *name; /* Read only after initialization! */
>>> +     struct kunit_try_catch try_catch;
>>>        /*
>>>         * success starts as true, and may only be set to false during a test
>>>         * case; thus, it is safe to update this across multiple threads using
>>> diff --git a/include/kunit/try-catch.h b/include/kunit/try-catch.h
>>> new file mode 100644
>>> index 0000000000000..404f336cbdc85
>>> --- /dev/null
>>> +++ b/include/kunit/try-catch.h
>>> @@ -0,0 +1,75 @@
>>> +/* SPDX-License-Identifier: GPL-2.0 */
>>> +/*
>>> + * An API to allow a function, that may fail, to be executed, and recover in a
>>> + * controlled manner.
>>> + *
>>> + * Copyright (C) 2019, Google LLC.
>>> + * Author: Brendan Higgins <brendanhiggins@google.com>
>>> + */
>>> +
>>> +#ifndef _KUNIT_TRY_CATCH_H
>>> +#define _KUNIT_TRY_CATCH_H
>>> +
>>> +#include <linux/types.h>
>>> +
>>> +typedef void (*kunit_try_catch_func_t)(void *);
>>> +
>>> +struct completion;
>>> +struct kunit;
>>> +
>>> +/**
>>> + * struct kunit_try_catch - provides a generic way to run code which might fail.
>>> + * @test: The test case that is currently being executed.
>>> + * @try_completion: Completion that the control thread waits on while test runs.
>>> + * @try_result: Contains any errno obtained while running test case.
>>> + * @try: The function, the test case, to attempt to run.
>>> + * @catch: The function called if @try bails out.
>>> + * @context: used to pass user data to the try and catch functions.
>>> + *
>>> + * kunit_try_catch provides a generic, architecture independent way to execute
>>> + * an arbitrary function of type kunit_try_catch_func_t which may bail out by
>>> + * calling kunit_try_catch_throw(). If kunit_try_catch_throw() is called, @try
>>> + * is stopped at the site of invocation and @catch is called.
>>> + *
>>> + * struct kunit_try_catch provides a generic interface for the functionality
>>> + * needed to implement kunit->abort() which in turn is needed for implementing
>>> + * assertions. Assertions allow stating a precondition for a test simplifying
>>> + * how test cases are written and presented.
>>> + *
>>> + * Assertions are like expectations, except they abort (call
>>> + * kunit_try_catch_throw()) when the specified condition is not met. This is
>>> + * useful when you look at a test case as a logical statement about some piece
>>> + * of code, where assertions are the premises for the test case, and the
>>> + * conclusion is a set of predicates, rather expectations, that must all be
>>> + * true. If your premises are violated, it does not makes sense to continue.
>>> + */
>>> +struct kunit_try_catch {
>>> +     /* private: internal use only. */
>>> +     struct kunit *test;
>>> +     struct completion *try_completion;
>>> +     int try_result;
>>> +     kunit_try_catch_func_t try;
>>> +     kunit_try_catch_func_t catch;
>>> +     void *context;
>>> +};
>>> +
>>> +void kunit_try_catch_init(struct kunit_try_catch *try_catch,
>>> +                       struct kunit *test,
>>> +                       kunit_try_catch_func_t try,
>>> +                       kunit_try_catch_func_t catch);
>>> +
>>> +void kunit_try_catch_run(struct kunit_try_catch *try_catch, void *context);
>>> +
>>> +void __noreturn kunit_try_catch_throw(struct kunit_try_catch *try_catch);
>>> +
>>> +static inline int kunit_try_catch_get_result(struct kunit_try_catch *try_catch)
>>> +{
>>> +     return try_catch->try_result;
>>> +}
>>> +
>>> +/*
>>> + * Exposed for testing only.
>>> + */
>>> +void kunit_generic_try_catch_init(struct kunit_try_catch *try_catch);
>>> +
>>> +#endif /* _KUNIT_TRY_CATCH_H */
>>> diff --git a/kunit/Makefile b/kunit/Makefile
>>> index 4e46450bcb3a8..c9176c9c578c6 100644
>>> --- a/kunit/Makefile
>>> +++ b/kunit/Makefile
>>> @@ -1,6 +1,7 @@
>>>    obj-$(CONFIG_KUNIT) +=                      test.o \
>>>                                        string-stream.o \
>>> -                                     assert.o
>>> +                                     assert.o \
>>> +                                     try-catch.o
>>>
>>>    obj-$(CONFIG_KUNIT_TEST) +=         string-stream-test.o
>>>
>>> diff --git a/kunit/test.c b/kunit/test.c
>>> index 3cbceb34b3b36..ded9895143209 100644
>>> --- a/kunit/test.c
>>> +++ b/kunit/test.c
>>> @@ -7,7 +7,9 @@
>>>     */
>>>
>>>    #include <kunit/test.h>
>>> +#include <kunit/try-catch.h>
>>>    #include <linux/kernel.h>
>>> +#include <linux/sched/debug.h>
>>>
>>>    static void kunit_set_failure(struct kunit *test)
>>>    {
>>> @@ -162,6 +164,19 @@ static void kunit_fail(struct kunit *test, struct kunit_assert *assert)
>>>        WARN_ON(string_stream_destroy(stream));
>>>    }
>>>
>>> +static void __noreturn kunit_abort(struct kunit *test)
>>> +{
>>> +     kunit_try_catch_throw(&test->try_catch); /* Does not return. */
>>> +
>>> +     /*
>>> +      * Throw could not abort from test.
>>> +      *
>>> +      * XXX: we should never reach this line! As kunit_try_catch_throw is
>>> +      * marked __noreturn.
>>> +      */
>>> +     BUG();
>>
>>
>> I recall discussion on this. What's the point in keeping thie
>> BUG() around when it doesn't even reach? It can even be a
>> WARN_ON() in that case right?
> 
> Originally I had BUG() here, and Frank (I think it was Frank, sorry it
> was a while ago) told me it should be WARN_ON(). In v12 Stephen told
> me it should be BUG(), and nobody objected so I went back to making it
> a BUG() (note I also mentioned this change on the cover letter of v13
> and still no one objected).
> 

Yeah. Sorry for the confusing advice. WARN_ON() or nothing is the right
thing here. I have been cleaning BUG() and WARN_ON() that aren't needed.

I would just delete BUG all together.

thanks,
-- Shuah