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Date:   Thu, 21 Mar 2019 18:41:46 -0700
From:   Brendan Higgins <brendanhiggins@...gle.com>
To:     Frank Rowand <frowand.list@...il.com>
Cc:     Kees Cook <keescook@...gle.com>,
        Luis Chamberlain <mcgrof@...nel.org>, shuah@...nel.org,
        Rob Herring <robh@...nel.org>,
        Kieran Bingham <kieran.bingham@...asonboard.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Joel Stanley <joel@....id.au>,
        Michael Ellerman <mpe@...erman.id.au>,
        Joe Perches <joe@...ches.com>, brakmo@...com,
        Steven Rostedt <rostedt@...dmis.org>,
        "Bird, Timothy" <Tim.Bird@...y.com>,
        Kevin Hilman <khilman@...libre.com>,
        Julia Lawall <julia.lawall@...6.fr>,
        linux-kselftest@...r.kernel.org, kunit-dev@...glegroups.com,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Jeff Dike <jdike@...toit.com>,
        Richard Weinberger <richard@....at>,
        linux-um@...ts.infradead.org, Daniel Vetter <daniel@...ll.ch>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Dan Williams <dan.j.williams@...el.com>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Knut Omang <knut.omang@...cle.com>,
        devicetree <devicetree@...r.kernel.org>,
        Petr Mladek <pmladek@...e.com>,
        Sasha Levin <Alexander.Levin@...rosoft.com>,
        Amir Goldstein <amir73il@...il.com>,
        Dan Carpenter <dan.carpenter@...cle.com>, wfg@...ux.intel.com
Subject: Re: [RFC v4 08/17] kunit: test: add support for test abort

On Thu, Mar 21, 2019 at 6:10 PM Frank Rowand <frowand.list@...il.com> wrote:
>
> On 2/27/19 11:42 PM, Brendan Higgins wrote:
> > On Tue, Feb 19, 2019 at 10:44 PM Frank Rowand <frowand.list@...il.com> wrote:
> >>
> >> On 2/19/19 7:39 PM, Brendan Higgins wrote:
> >>> On Mon, Feb 18, 2019 at 11:52 AM Frank Rowand <frowand.list@...il.com> wrote:
> >>>>
> >>>> On 2/14/19 1:37 PM, Brendan Higgins wrote:
> >>>>> Add support for aborting/bailing out of test cases. Needed for
> >>>>> implementing assertions.
> >>>>>
> >>>>> Signed-off-by: Brendan Higgins <brendanhiggins@...gle.com>
> >>>>> ---
> >>>>> Changes Since Last Version
> >>>>>  - This patch is new introducing a new cross-architecture way to abort
> >>>>>    out of a test case (needed for KUNIT_ASSERT_*, see next patch for
> >>>>>    details).
> >>>>>  - On a side note, this is not a complete replacement for the UML abort
> >>>>>    mechanism, but covers the majority of necessary functionality. UML
> >>>>>    architecture specific featurs have been dropped from the initial
> >>>>>    patchset.
> >>>>> ---
> >>>>>  include/kunit/test.h |  24 +++++
> >>>>>  kunit/Makefile       |   3 +-
> >>>>>  kunit/test-test.c    | 127 ++++++++++++++++++++++++++
> >>>>>  kunit/test.c         | 208 +++++++++++++++++++++++++++++++++++++++++--
> >>>>>  4 files changed, 353 insertions(+), 9 deletions(-)
> >>>>>  create mode 100644 kunit/test-test.c
> >>>>
> >>>> < snip >
> >>>>
> >>>>> diff --git a/kunit/test.c b/kunit/test.c
> >>>>> index d18c50d5ed671..6e5244642ab07 100644
> >>>>> --- a/kunit/test.c
> >>>>> +++ b/kunit/test.c
> >>>>> @@ -6,9 +6,9 @@
> >>>>>   * Author: Brendan Higgins <brendanhiggins@...gle.com>
> >>>>>   */
> >>>>>
> >>>>> -#include <linux/sched.h>
> >>>>>  #include <linux/sched/debug.h>
> >>>>> -#include <os.h>
> >>>>> +#include <linux/completion.h>
> >>>>> +#include <linux/kthread.h>
> >>>>>  #include <kunit/test.h>
> >>>>>
> >>>>>  static bool kunit_get_success(struct kunit *test)
> >>>>> @@ -32,6 +32,27 @@ static void kunit_set_success(struct kunit *test, bool success)
> >>>>>       spin_unlock_irqrestore(&test->lock, flags);
> >>>>>  }
> >>>>>
> >>>>> +static bool kunit_get_death_test(struct kunit *test)
> >>>>> +{
> >>>>> +     unsigned long flags;
> >>>>> +     bool death_test;
> >>>>> +
> >>>>> +     spin_lock_irqsave(&test->lock, flags);
> >>>>> +     death_test = test->death_test;
> >>>>> +     spin_unlock_irqrestore(&test->lock, flags);
> >>>>> +
> >>>>> +     return death_test;
> >>>>> +}
> >>>>> +
> >>>>> +static void kunit_set_death_test(struct kunit *test, bool death_test)
> >>>>> +{
> >>>>> +     unsigned long flags;
> >>>>> +
> >>>>> +     spin_lock_irqsave(&test->lock, flags);
> >>>>> +     test->death_test = death_test;
> >>>>> +     spin_unlock_irqrestore(&test->lock, flags);
> >>>>> +}
> >>>>> +
> >>>>>  static int kunit_vprintk_emit(const struct kunit *test,
> >>>>>                             int level,
> >>>>>                             const char *fmt,
> >>>>> @@ -70,13 +91,29 @@ static void kunit_fail(struct kunit *test, struct kunit_stream *stream)
> >>>>>       stream->commit(stream);
> >>>>>  }
> >>>>>
> >>>>> +static void __noreturn kunit_abort(struct kunit *test)
> >>>>> +{
> >>>>> +     kunit_set_death_test(test, true);
> >>>>> +
> >>>>> +     test->try_catch.throw(&test->try_catch);
> >>>>> +
> >>>>> +     /*
> >>>>> +      * Throw could not abort from test.
> >>>>> +      */
> >>>>> +     kunit_err(test, "Throw could not abort from test!");
> >>>>> +     show_stack(NULL, NULL);
> >>>>> +     BUG();
> >>>>
> >>>> kunit_abort() is what will be call as the result of an assert failure.
> >>>
> >>> Yep. Does that need clarified somewhere.
> >>>>
> >>>> BUG(), which is a panic, which is crashing the system is not acceptable
> >>>> in the Linux kernel.  You will just annoy Linus if you submit this.
> >>>
> >>> Sorry, I thought this was an acceptable use case since, a) this should
> >>> never be compiled in a production kernel, b) we are in a pretty bad,
> >>> unpredictable state if we get here and keep going. I think you might
> >>> have said elsewhere that you think "a" is not valid? In any case, I
> >>> can replace this with a WARN, would that be acceptable?
> >>
> >> A WARN may or may not make sense, depending on the context.  It may
> >> be sufficient to simply report a test failure (as in the old version
> >> of case (2) below.
> >>
> >> Answers to "a)" and "b)":
> >>
> >> a) it might be in a production kernel
> >
> > Sorry for a possibly stupid question, how might it be so? Why would
> > someone intentionally build unit tests into a production kernel?
>
> People do things.  Just expect it.

Huh, alright. I will take your word for it then.

>
> >>
> >> a') it is not acceptable in my development kernel either
> >
> > Fair enough.
> >
> >>
> >> b) No.  You don't crash a developer's kernel either unless it is
> >> required to avoid data corruption.
> >
> > Alright, I thought that was one of those cases, but I am not going to
> > push the point. Also, in case it wasn't clear, the path where BUG()
> > gets called only happens if there is a bug in KUnit itself, not just
> > because a test case fails catastrophically.
>
> Still not out of the woods.  Still facing Lions and Tigers and Bears,
> Oh my!

Nope, I guess not :-)

>
> So kunit_abort() is normally called as the result of an assert
> failure (as written many lines further above).
>
> kunit_abort()
>    test->try_catch.throw(&test->try_catch)
>    // this is really kunit_generic_throw(), yes?
>       complete_and_exit()
>          if (comp)
>             // comp is test_case_completion?
>             complete(comp)
>          do_exit()
>             // void __noreturn do_exit(long code)
>             // depending on the task, either panic
>             // or the task dies

You are right up until after it calls do_exit().

KUnit actually spawns a thread for the test case to run in so that
when exit is called, only the test case thread dies. The thread that
started KUnit is never affected.

>
> I did not read through enough of the code to understand what is going
> on here.  Is each kunit_module executed in a newly created thread?
> And if kunit_abort() is called then that thread dies?  Or something
> else?

Mostly right, each kunit_case (not kunit_module) gets executed in its
own newly created thread. If kunit_abort() is called in that thread,
the kunit_case thread dies. The parent thread keeps going, and other
test cases are executed.

>
>
> >>
> >> b') And you can not do replacements like:
> >>
> >> (1) in of_unittest_check_tree_linkage()
> >>
> >> -----  old  -----
> >>
> >>         if (!of_root)
> >>                 return;
> >>
> >> -----  new  -----
> >>
> >>         KUNIT_ASSERT_NOT_ERR_OR_NULL(test, of_root);
> >>
> >> (2) in of_unittest_property_string()
> >>
> >> -----  old  -----
> >>
> >>         /* of_property_read_string_index() tests */
> >>         rc = of_property_read_string_index(np, "string-property", 0, strings);
> >>         unittest(rc == 0 && !strcmp(strings[0], "foobar"), "of_property_read_string_index() failure; rc=%i\n", rc);
> >>
> >> -----  new  -----
> >>
> >>         /* of_property_read_string_index() tests */
> >>         rc = of_property_read_string_index(np, "string-property", 0, strings);
> >>         KUNIT_ASSERT_EQ(test, rc, 0);
> >>         KUNIT_EXPECT_STREQ(test, strings[0], "foobar");
> >>
> >>
> >> If a test fails, that is no reason to abort testing.  The remainder of the unit
> >> tests can still run.  There may be cascading failures, but that is ok.
> >
> > Sure, that's what I am trying to do. I don't see how (1) changes
> > anything, a failed KUNIT_ASSERT_* only bails on the current test case,
> > it does not quit the entire test suite let alone crash the kernel.
>
> This may be another case of whether a kunit_module is approximately a
> single KUNIT_EXPECT_*() or a larger number of them.
>
> I still want, for example, of_unittest_property_string() to include a large
> number of KUNIT_EXPECT_*() instances.  In that case I still want the rest of
> the tests in the kunit_module to be executed even after a KUNIT_ASSERT_*()
> fails.  The existing test code has that property.

Sure, in the context of the reply you just sent me on the DT unittest
thread, that makes sense. I can pull out all but the ones that would
have terminated the collection of test cases (where you return early),
if that makes it better.

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