linux-kernel - Re: [PATCH] module: kunit: Load .kunit_test_suites section when CONFIG

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Date:   Wed, 20 Jul 2022 13:29:09 -0700
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     David Gow <davidgow@...gle.com>
Cc:     Daniel Latypov <dlatypov@...gle.com>,
        Brendan Higgins <brendanhiggins@...gle.com>,
        Shuah Khan <skhan@...uxfoundation.org>,
        Jeremy Kerr <jk@...econstruct.com.au>,
        linux-modules@...r.kernel.org,
        KUnit Development <kunit-dev@...glegroups.com>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] module: kunit: Load .kunit_test_suites section when
 CONFIG_KUNIT=m

On Wed, Jul 20, 2022 at 05:26:02PM +0800, David Gow wrote:
> On Wed, Jul 20, 2022 at 1:58 AM Luis Chamberlain <mcgrof@...nel.org> wrote:
> >
> > On Wed, Jul 13, 2022 at 08:24:32AM -0700, Daniel Latypov wrote:
> > > On Tue, Jul 12, 2022 at 5:52 PM David Gow <davidgow@...gle.com> wrote:
> > > >
> > > > The new KUnit module handling has KUnit test suites listed in a
> > > > .kunit_test_suites section of each module. This should be loaded when
> > > > the module is, but at the moment this only happens if KUnit is built-in.
> > > >
> > > > Also load this when KUnit is enabled as a module: it'll not be usable
> > > > unless KUnit is loaded, but such modules are likely to depend on KUnit
> > > > anyway, so it's unlikely to ever be loaded needlessly.
> > >
> > > This seems reasonable to me.
> > >
> > > Question: what happens in this case?
> > > 1. insmod <test-module>
> > > 2. insmod kunit
> > > 3. rmmod <test-module>
> > >
> > > I think on 3, we'll call the cleanup code, __kunit_test_suites_exit(),
> > > for <test-module>, I think?
> > > But we never called __kunit_test_suites_init().
> > > My fear is what breaks as a result of this precondition break.
> 
> I don't think this should be possible: any module with KUnit tests
> will depend on the 'kunit' module (or, at least, kunit symbols), so
> shouldn't load without kunit already present.
> 
> If modprobe is used, kunit will automatically be loaded. If insmod is
> used directly, loading the first module should error out with
> something like:
> [   82.393629] list_test: loading test module taints kernel.
> [   82.409607] list_test: Unknown symbol kunit_binary_ptr_assert_format (err -2)
> [   82.409657] list_test: Unknown symbol kunit_do_failed_assertion (err -2)
> [   82.409799] list_test: Unknown symbol kunit_binary_assert_format (err -2)
> [   82.409820] list_test: Unknown symbol kunit_unary_assert_format (err -2)
> insmod: ERROR: could not insert module
> /lib/modules/5.19.0-rc1-15284-g9ec67db0c271/kernel/lib/list-test.ko:
> Unknown symbol in module

This can be fixed with a request_module() call. And since this is a
generic requirement, you can have the wrappers do it for you.

> Maybe you could get into some trouble by force-removing modules at
> various points, but you're in undefined behaviour generally at that
> point, so I don't think there's much point going out-of-our-way to try
> to support that.

You can prevent that by refcounting the kunit module / symbols, by each test.

  Luis