linux-kernel - Re: [PATCH v5 1/2] kunit: drop assumption in kunit-log-test about current suite

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Date:   Wed, 22 Sep 2021 00:04:35 +0800
From:   David Gow <davidgow@...gle.com>
To:     Daniel Latypov <dlatypov@...gle.com>
Cc:     Brendan Higgins <brendanhiggins@...gle.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        KUnit Development <kunit-dev@...glegroups.com>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH v5 1/2] kunit: drop assumption in kunit-log-test about
 current suite

On Wed, Sep 15, 2021 at 5:03 AM Daniel Latypov <dlatypov@...gle.com> wrote:
>
> This test assumes that the declared kunit_suite object is the exact one
> which is being executed, which KUnit will not guarantee [1].
>
> Specifically, `suite->log` is not initialized until a suite object is
> executed. So if KUnit makes a copy of the suite and runs that instead,
> this test dereferences an invalid pointer and (hopefully) segfaults.
>
> N.B. since we no longer assume this, we can no longer verify that
> `suite->log` is *not* allocated during normal execution.
>
> An alternative to this patch that would allow us to test that would
> require exposing an API for the current test to get its current suite.
> Exposing that for one internal kunit test seems like overkill, and
> grants users more footguns (e.g. reusing a test case in multiple suites
> and changing behavior based on the suite name, dynamically modifying the
> setup/cleanup funcs, storing/reading stuff out of the suite->log, etc.).
>
> [1] In a subsequent patch, KUnit will allow running subsets of test
> cases within a suite by making a copy of the suite w/ the filtered test
> list. But there are other reasons KUnit might execute a copy, e.g. if it
> ever wants to support parallel execution of different suites, recovering
> from errors and restarting suites
>
> Signed-off-by: Daniel Latypov <dlatypov@...gle.com>
> Reviewed-by: Brendan Higgins <brendanhiggins@...gle.com>
> ---
Thanks for fixing this.

I do think that using "fake" tests/suites like this in more cases will
unlock testing other parts of KUnit as well.

Reviewed-by: David Gow <davidgow@...gle.com>

Cheers,
-- David


>  lib/kunit/kunit-test.c | 14 ++++++++------
>  1 file changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/lib/kunit/kunit-test.c b/lib/kunit/kunit-test.c
> index d69efcbed624..555601d17f79 100644
> --- a/lib/kunit/kunit-test.c
> +++ b/lib/kunit/kunit-test.c
> @@ -415,12 +415,15 @@ static struct kunit_suite kunit_log_test_suite = {
>
>  static void kunit_log_test(struct kunit *test)
>  {
> -       struct kunit_suite *suite = &kunit_log_test_suite;
> +       struct kunit_suite suite;
> +
> +       suite.log = kunit_kzalloc(test, KUNIT_LOG_SIZE, GFP_KERNEL);
> +       KUNIT_ASSERT_NOT_ERR_OR_NULL(test, suite.log);
>
>         kunit_log(KERN_INFO, test, "put this in log.");
>         kunit_log(KERN_INFO, test, "this too.");
> -       kunit_log(KERN_INFO, suite, "add to suite log.");
> -       kunit_log(KERN_INFO, suite, "along with this.");
> +       kunit_log(KERN_INFO, &suite, "add to suite log.");
> +       kunit_log(KERN_INFO, &suite, "along with this.");
>
>  #ifdef CONFIG_KUNIT_DEBUGFS
>         KUNIT_EXPECT_NOT_ERR_OR_NULL(test,
> @@ -428,12 +431,11 @@ static void kunit_log_test(struct kunit *test)
>         KUNIT_EXPECT_NOT_ERR_OR_NULL(test,
>                                      strstr(test->log, "this too."));
>         KUNIT_EXPECT_NOT_ERR_OR_NULL(test,
> -                                    strstr(suite->log, "add to suite log."));
> +                                    strstr(suite.log, "add to suite log."));
>         KUNIT_EXPECT_NOT_ERR_OR_NULL(test,
> -                                    strstr(suite->log, "along with this."));
> +                                    strstr(suite.log, "along with this."));
>  #else
>         KUNIT_EXPECT_PTR_EQ(test, test->log, (char *)NULL);
> -       KUNIT_EXPECT_PTR_EQ(test, suite->log, (char *)NULL);
>  #endif
>  }
>
>
> base-commit: 316346243be6df12799c0b64b788e06bad97c30b
> --
> 2.33.0.309.g3052b89438-goog
>