Re: [RFC v4 08/17] kunit: test: add support for test abort

Frank Rowand
2019-03-22T01:10:01Z

On 2/27/19 11:42 PM, Brendan Higgins wrote:
> On Tue, Feb 19, 2019 at 10:44 PM Frank Rowand <frowand.list@gmail.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@gmail.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@google.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@google.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.