Message-ID: <CAFd5g451bF2-RGZ3wT9gO1FOu+8e8yQO9evvxtQQ9Vkh4UUhVQ@mail.gmail.com>
Date:   Fri, 23 Aug 2019 09:56:23 -0700
From:   Brendan Higgins <brendanhiggins@...gle.com>
To:     shuah <shuah@...nel.org>
Cc:     Frank Rowand <frowand.list@...il.com>,
        Greg KH <gregkh@...uxfoundation.org>,
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        Peter Zijlstra <peterz@...radead.org>,
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        "Theodore Ts'o" <tytso@....edu>,
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Subject: Re: [PATCH v14 09/18] kunit: test: add support for test abort

On Fri, Aug 23, 2019 at 8:36 AM shuah <shuah@...nel.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@...gle.com>
> > Reviewed-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > Reviewed-by: Logan Gunthorpe <logang@...tatee.com>
> > Reviewed-by: Stephen Boyd <sboyd@...nel.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@...gle.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).

You can see the most recent discussion with Stephen here:
https://lore.kernel.org/linux-kselftest/20190812182421.141150-1-brendanhiggins@google.com/T/#mb108adc525092dd72fd3368ecae34251bad29edf

Cheers

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