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Date:   Thu, 21 Mar 2019 18:09:55 -0700
From:   Frank Rowand <frowand.list@...il.com>
To:     Brendan Higgins <brendanhiggins@...gle.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@...cle.com,
        wfg@...ux.intel.com, Frank Rowand <frowand.list@...il.com>
Subject: Re: [RFC v4 08/17] kunit: test: add support for test abort

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.


>>
>> 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!

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

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?


>>
>> 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.


> 
> In case it wasn't clear above,
>>>>> +     test->try_catch.throw(&test->try_catch);
> should never, ever return. The only time it would, would be if KUnit
> was very broken. This should never actually happen, even if the
> assertion that called it was violated. KUNIT_ASSERT_* just says, "this
> is a prerequisite property for this test case"; if it is violated, the
> test case should fail and bail because the preconditions for the test
> case cannot be satisfied. Nevertheless, other tests cases will still
> run.
> 

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