linux-kernel - Re: [RFC] drm/tests: annotate intentional stack trace in drm_test_rect_calc

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Message-ID: <s4blvjs4ipcqdzodmgsbvgegqh2kxgdnoerpwthvc57hpsulu5@gb2kh7vbv7nq>
Date:   Mon, 6 Nov 2023 14:58:12 +0100
From:   mripard@...nel.org
To:     Dan Carpenter <dan.carpenter@...aro.org>
Cc:     Naresh Kamboju <naresh.kamboju@...aro.org>,
        Richard Fitzgerald <rf@...nsource.cirrus.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Kees Cook <keescook@...omium.org>,
        Daniel Díaz <daniel.diaz@...aro.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Brendan Higgins <brendan.higgins@...ux.dev>,
        David Gow <davidgow@...gle.com>,
        Maíra Canal <mcanal@...lia.com>,
        Arthur Grillo <arthurgrillo@...eup.net>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, kunit-dev@...glegroups.com,
        kernel-janitors@...r.kernel.org,
        Ville Syrjälä <ville.syrjala@...ux.intel.com>,
        kv-team <kv-team@...aro.org>
Subject: Re: [RFC] drm/tests: annotate intentional stack trace in
 drm_test_rect_calc_hscale()

Hi,

On Wed, Nov 01, 2023 at 12:08:00PM +0300, Dan Carpenter wrote:
> Let me add Richard to the CC list.  See lore for more details.
> https://lore.kernel.org/all/CA+G9fYuA643RHHpPnz9Ww7rr3zV5a0y=7_uFcybBSL=QP_sQvQ@mail.gmail.com/
> 
> On Tue, Oct 31, 2023 at 09:57:48PM +0530, Naresh Kamboju wrote:
> > On Mon, 30 Oct 2023 at 14:33, Dan Carpenter <dan.carpenter@...aro.org> wrote:
> > >
> > > We have started printing more and more intentional stack traces.  Whether
> > > it's testing KASAN is able to detect use after frees or it's part of a
> > > kunit test.
> > >
> > > These stack traces can be problematic.  They suddenly show up as a new
> > > failure.  Now the test team has to contact the developers.  A bunch of
> > > people have to investigate the bug.  We finally decide that it's
> > > intentional so now the test team has to update their filter scripts to
> > > mark it as intentional.  These filters are ad-hoc because there is no
> > > standard format for warnings.
> > >
> > > A better way would be to mark it as intentional from the start.
> > >
> > > Here, I have marked the beginning and the end of the trace.  It's more
> > > tricky for things like lkdtm_FORTIFY_MEM_MEMBER() where the flow doesn't
> > > reach the end of the function.  I guess I would print a different
> > > warning for stack traces that can't have a
> > > "Intentional warning finished\n" message at the end.
> > >
> > > I haven't actually tested this patch...  Daniel, do you have a
> > > list of intentional stack traces we could annotate?
> > 
> > [My two cents]
> > 
> > I have been noticing following kernel warnings / BUGs
> 
> Some are intentional and some are not.  I had a similar thing happen to
> me last week where I had too many Smatch false positives in my devel
> code so I accidentally sent a patch with a stupid bug.  I've since
> updated my QC process to run both the devel and released versions of
> Smatch.
> 
> But a similar thing is happening here where we have so many bogus
> warnings that we missed a real bug.

IIRC, there was a similar discussion for lockdep issues. IMO, any
(unintended) warning should trigger a test failure.

I guess that would require adding some intrumentation to __WARN somehow,
and also allowing tests to check whether a warning had been generated
during their execution for tests that want to trigger one.

Maxime

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